Quarter Scale Merlin V-12

[Ken I]

Cast Iron bar stock is frequently spun cast and can have all sorts of spiral graining and residual stresses in it.
Best to rough machine it, heat treat it / normalise - then ideally let it age a bit before final machining.

It can even be a sod to simply drill a straight hole down the centre.

And quality can vary wildly.

Regards,
Ken

 

[Charles Lamont]

All the c.i. material used in the V-4 was class 40 cast iron, but it had been purchased at different times from different suppliers and was, in fact, remnants from other projects I had been involved with. I had trouble with the rings sealing on the V-4, and after checking the ring fit of my first set of liners with a light source, I traced the problem to the liners, themselves, which weren't perfectly circular. After discovering that I actually needed to measure the circularity of the liners with a dial bore gage after they were machined instead of just assuming they were perfect, I learned just how difficult it was to not only machine a thin-wall slip-in liner truly circular but also how difficult it was get it to remain so.

You don't lap the bores?

 

[mayhugh1]

You don't lap the bores?

Charles,
At that time on my experience curve I was using abrasive brush hones to hone the bores, but I've since swiched to laps. With the honing, I had problems with the workholding distorting the thin liners while they were being honed. My 5C collets were a major disapointment as supports, and I eventually learned I had to hold them lightly in a gloved hand with the hone in a battery-powered electric drill in the other hand. After I finally got the workholding 'in hand', I then learned about the issues involved with the material settling out days afterward and putting everything back to square one. I've used cast iron only for rings since that experience. On my last engine I heated the ring material up for several hours at 600F before roughing out the rings. I then left the material alone for several days before finishing them. I got pretty good yields on some 80 rings I made on my 18 cylinder radial. I'd have to look back in my notes to be sure, but I seem to recall it was on the order of 80%-90%.
I'm sure thick wall liners would be less of a problem especially if they could be lapped after being pressed into the block. In my experience, thin-wall slip-in liners are quite a challenge. -Terry

 

[Parksy]

I'm curious as to how thin these liners were that you speak of Terry?

 

[mayhugh1]

I'm curious as to how thin these liners were that you speak of Terry?

Parksy,
The V-4 liners were 1/16" thick. The stock Merlin's were 1/32".
Terry

 

[mayhugh1]

With a set of revised drawings, I went back into my shop and began working on the cylinder liners. I decided to start out using 1144 (Stressproof) for the liner material because of its reputation for dimensional stability during and after machining. Even with thicker walls, cast iron still didn't seem like the right material for these particular liners because of their protruding top ends used to seal the combustion chambers. Cast iron in these thin and highly stressed sections could potentially crack when the head assemblies are torqued down to the cylinder blocks. Similar problems, believed to have been created by the rapid temperature changes inside the combustion chambers did actually plague the early full-scale Merlins. The Quarter Scale's liner drawing specifies chrome moly which is similar to the alloy used in the full-size liners. I added it to my short list of alternatives along with 12L14 in case 1144 didn't work out.

My only experience with Stressproof has been with a handful of parts machined for this engine including, of course, its crankshaft. I found it easy to obtain beautiful surface finishes except for a single lathe boring operation that I had briefly tried as a test. Although 1144 is generally considered to be free machining, its machinability is half that of 12L14, and it is 50% harder. Boring bar chatter, which I've always been able to control while machining 12L14 or 303, left me with a concern about using Stressproof for the liners.

Before fully committing to it, I thought I would perform some experiments to see if my equipment and I were capable of obtaining usable surface finishes inside the Merlin's 1.2" diameter by 2.5" deep liner bores. Although the liners will eventually be lapped, I've learned that it's best to begin the lapping process with smooth bores that are within a couple thousandths of their finished diameters. Light imperfections are easily removed, but starting out to lap three or more thousandths from a large number of undersize bores or bores with heavy chatter patterns can be the beginning of a long and messy weekend.

I saw-cut several 1-5/8" diameter Stressproof blanks that I hoped would eventually become liners. These were drilled through at 1-1/8" diameter so I could practice the boring operation on them before taking any to their final diameter. Drilling such large deep through-holes on my 12x36 manual Enco lathe turned into a grueling experience of its own. I used four tailstock drills ranging in size from 1/2" to 1-1/8". I found it best to turn entry chamfers on the blanks for the larger drills in order to cut down the excitement created while trying to get the drills' cutting edges started. There was just no rpm setting that would keep the lathe happy about what it was being forced to do. Running in its back gear at 100 rpm sometimes resulted in severe dig-in's when my tailstock feed rate got a little ahead of the spindle speed. Increasing the spindle speed to a couple hundred rpm without the back gear created bone-chilling chatter until the drill was well inside the blank. Spindle stalling then became a problem due to the lathe's drive belt slipping when, again, the feed rate wasn't just right. Initially, the drilling required about 30 minutes per blank, but it stretched out to some 45 minutes as the drills dulled.

I ended up running tests on four blanks before deciding to continue using 1144. Initial tests showed that my 9x20 CNC lathe was only marginally capable of the required boring operation. I was hoping to use this lathe since I get better repeatability on large lots of parts when I let the computer take my place cranking the hand wheels. I had previously gotten good results while turning smaller diameter 1144 parts on this lathe at 300 SFM. But, once my 5/8" boring bar with its 2-1/2" stick out started to feed into the 1-1/8" bore, I had chatter problems that seemed insolvable. The 9x20 lathes are notorious for rigidity issues associated with their lightweight compound. I wouldn't even have attempted this operation on an unmodified 9x20, but I had long ago replaced my lathe's compound with a huge block of metal. I could dial in any feed rate I wanted, but at this bore diameter the lathe was limited to a minimum SFM of about 100 by the low end torque available from its very expensive Varicon motor and its lack of a back gear. This particular boring operation really needed to be run at a much slower rpm in order to control the chatter.

My best obtainable surface finish was disappointing and had a very prominent chatter pattern. Similar operations on free machining steels using the same lathe and tooling had always produced much better results. Early in these tests I found it necessary to move away from finishing inserts with chip breakers intended to cut steel and instead used very sharp high rake inserts designed for aluminum. My lathe was just too lightweight to handle the d.o.c.'s required for the steel-cutting inserts on 1144. Using Korloy aluminum cutting inserts, I found I could take d.o.c.'s (dia.) anywhere between .005" and .040".

I was finally able to get marginally acceptable results by modifying a 3/4" boring bar that had been purchased as part of a set but never used because it was too large for my lathes' tool holders. After grinding down a portion of it so it could be clamped in my 9x20 tool holder, the chatter improved somewhat. The periodic pattern disappeared, but the surface finish still had rather deep ridges that I could feel.

In the midst of all these poor results I needed a sanity check to make sure my recollections of turning this stuff on this lathe hadn't been imagined. Sure enough, I was able to easily turn the 1.625" o.d. of the blanks at 500 SFM using .0025 in/rev and an inexpensive insert designed for finishing steel. The surface finish was a nearly perfect mirror.

So, I moved the modified boring bar to the Enco lathe where I was able to use the lathe's back gear to drop the surface speed down to about 30 SFM. The finish improved enough for me to feel better about continuing with 1144 for the liners. I saw-cut a total of 15 blanks, pre-drilled them, and then finish bored their i.d.'s to 1.200" +0/-.001". The o.d.'s of the blanks in the photos may appear to have also been machined, but this is because I mistakenly ordered the starting material I had been using as 'ground and polished.' The next step will be to prepare an expanding mandrel to grip the bores in the lathe chuck so the features on the o.d.'s can be turned. - Terry

 

[petertha]

Nice. Watching this closely. Very interesting on the insert cutter results. I bought a stick of 1144SP myself to try. Flying season is drawing to a close but you are making me itchy to return to the shop early. I found pre-drilling the holes kind of PITA too. Not so much the progressive size drudgery, but axial pressure wanting to push the slug against chuck jaws. Its an accurate chuck but I also didn't want to gorilla crank down & distort the thin wall. My liners require a lip anyway so roughed in that feature & that acted as a stop against the chuck jaws which helped.

Any thoughts on using these annular cutters?

 

[Buchanan]

We regularly use annular cutters to bulk remove metal . I have an adapter that fits into my tail stock taper that holds the cutter in a socket with a couple of grub screws. The only limitation is the max depth but often the job can be turned around and a 4 inch hole can be achieved. Much less swaf and a nice slug left for something else. The hole size is good and few starting problems.
I love your work Terry

 

[lohring]

A very long time ago my company had a customer who needed to bore long, accurate holes in tubing. He also needed a good surface finish that he was getting by honing after boring. We made him a cutter with two square inserts set on opposite sides at a 45 degree angle. The points were circularly ground to the finish diameter. That makes the front of the inserts the cutting side, just like a drill or reamer. We then made him a bar that PULLED the cutter through the tubing.

Our customer was then able to finish the bore with one pass and get both the diametric accuracy and surface finish he needed. The secret was pulling rather than trying to push a long boring bar and the self centering effect of the circularly ground inserts. Of course the starting hole needs to be concentric and straight. In your case if the hole is bored first the OD can be machined with the liner in an arbor.

Lohring Miller

 

[mayhugh1]

[Quote: Any thoughts on using these annular cutters?]

I've seen these on consignment tables at shows but never gave them much thought because I didn't appreciate what they were used for. Now I wish I'd picked up a few. I like the idea of not having to turn the whole bore into chips, but I wonder if a large one would be easier to start into a piece of steel chucked in my lathe. If not, I'm pretty sure my Bridgeport clone could handle it. - Terry

 

[Buchanan]

I have used them both in a Bridgeport and a 1963 Colchester student tailstock and they start easily (with a slow start feed and normal care) I really like them. They do need coolant and make long thin stringy swarf, but if you back off the cutter often it is nor a problem, we use a 31mm diameter in a Bridgeport to drill holes through 45mm thick wall tube at a 27 degree angle for hand rails. You can see the waste slug on the top slide of the lathe. this was cut from both sides. We use bath HSS and carbide tipped. The carbide are faster, you can push them harder.

 

[wirralcnc]

Terry
These are brilliant. Used them for many years. Known as rotabroach if you want to Google them. Usually have a centering pin which when used in the rotabroach holder becomes spring loaded. Can be used without centre pin and still remain very stable. In my experiences with them you need to keep weight on them or you lose the cutting edge.

 

[bigrigbri]

I would hone/lap the bores to size first after finishing the o/l.
Placing the finished bore on a close fitting expanding mandrel or a threaded and bolted one to ensure concentricity.
Working prevoiusly at a company for 20 years making liners from 2" to 24" bore this type of machining operation was often used. Liners can be de mounted for testing and re machined with no set up necessary keeping a good roundness through the bore.

 

[mayhugh1]

In order to turn the liners' o.d. features, they were supported by their bores on an expanding collet. Although many builders routinely make such mandrels, I opted to use a commercial import that threads into a 5C collet chuck. Once installed, it was turned to fit the liner bores and then left in place on the lathe until all the machining on all the liners was completed. Before turning the soft collet for a close slip fit inside the bores, it was important to place the collet segments under a bit of outward pressure using their expanding screw. The total available adjustment range was only some ten thousandths, and since this corresponded to about a quarter turn, an initial loading of 1/16 turn was sufficient.

Unfortunately, the runout measured at the mandrel's tailstock end varied as much as a couple thousandths when the screw was adjusted for a different diameter. The workpiece couldn't be arbitrarily taken off and on the mandrel nor flipped end-for-end between operations intended for perfectly concentric features (maybe because the bores hadn't yet been honed as 'Bigrigbri' suggested.) Since this was how I planned to use the mandrel, I had to re-indicate the workpiece each time it was remounted. This involved rotating the workpiece on the mandrel, tightening the expanding screw, indicating the o.d. used as a reference and then repeating the steps until the minimum TIR was found. Fortunately, it was always within a half thousandth or so. There were only a few features on the liners that needed to be truly concentric, but I chose to re-indicate each workpiece before every operation. Witness marks added to the i.d. of each liner with a marking pen eventually eliminated the tedious process.

One of the sketches shows the liners' features that required machining. For consistency, all the liners were machined in batches one feature at a time. A real risk with this approach, though, was that an error could have propagated throughout the whole batch of parts before being discovered. Features one and three are the most critical, and these must be concentric with each other. Feature one is the lower half of the combustion chamber seal, and number three is the lower half of the coolant jacket's upper seal.

Feature one was the first turning operation, and it also became the reference o.d. for indicating all subsequent operations. Counterbores in the heads' combustion chambers will seal against the top ends of the liners which sit above the cylinder block. These seals rely on an important machining detail described by a pair of notes - "no sharp inside corners" and ".010 R Fillet Typ" - on the drawing for the liner. I've included a close-up sketch of the area of interest for a typical seal.

A 1.405" diameter counterbore, concentric with each combustion chamber, was machined into the heads much earlier. The top end of each liner was specified to be turned with an outside diameter of 1.400" as well as a .010" radius fillet in its outside corner. It's very important that the ends of all six liners sit at the exact same height above the top surface of the cylinder block. When the head is bolted down to the block, the liners are sandwiched between them, and the sharp edge of the counterbores are forced into the liners' outside fillets to create the seals. Modeling showed there should be a .003" crush height available for deforming the soft edge of the aluminum counterbore into the hard corner fillet of the liner. Since I turned the ends of my liners using a standard lathe insert with a .008" nose radius instead of grinding a custom .010" radius cutter, I changed the outer diameter of the liners' top ends to 1.402" to obtain the same .003" crush height.

The integrity of the seals also relies on machining that was done over a year ago when the head and cylinder block castings were bored. During those operations it was important to accurately machine all the counterbores to the same diameter and spacing to match the bores in the cylinder blocks. I was anal about machining all the counterbores on both heads to within a few tenths of one another so a common end diameter could be later used for all the liners. Back in post #61, just after completing the head and cylinder block machining, I turned a set of close-fitting Delrin fixtures which simulate a portion of the liners including their top ends and shoulders. I used them to trial assemble the head and cylinder block pairs just after machining them so I could verify the counterbores in the heads were actually aligned with the cylinder bores in the blocks. This had been one of my 'must have' machining milestones in this build.

After the top end of the first liner was machined, it was lightly set into each head counterbore so the crush distance could be checked with a feeler gage. Depending upon the particular counterbore used for the measurement, the crush heights ranged from zero to something under .001", but most were close to zero. The explanation for this that I took away from the modeling was that even though the 'sharp' edges of the counterbores had never been intentionally broken, they likely ended up with slight chamfers up to .004" in width. I turned this into an opportunity to improve the seal by turning two different radii fillets at two different depths on the liners. I've included a drawing from my modeling to illustrate just what I actually did. Basically, a typical counterbore's chamfered edge fits nicely into the .008" radius fillet, and the .016" fillet provides a additional crush height of .002". These fillet radii match the nose radii of standard lathe inserts. The crush heights of the finally machined parts measured between .0015" and .002".

The outside diameter of each blank was next turned down to 1.500" which became the final o.d. of the liner's top shoulder as well as its largest diameter feature. A fixture was then machined for the headstock end of the mandrel to use as a positive z-axis stop. The blanks were then reversed on the mandrel with their finished top ends tightly against this stop so each could be faced to the exact same final length. This stop was used to reference the z-axis for the rest of the operations.

The coolant jacket was then machined using a DCMT insert. This 55 degree rhomboid cutter simplified the turning operation and left good looking tapered edges at the ends of the jackets. The recessed jacket provided a nice tool entry point for finish machining the coolant jacket's upper seal using a grooving tool modified with a bit of relief so it could be used for very light side-to-side turning.

The number three feature is the lower half of the coolant jacket's top seal. The liner diameter just below the shoulder was specified to have a close slip fit in the cylinder block, but since it's not a press fit, it's not a functional seal either. Instead, the seal is formed between the top deck surface of the cylinder block and the bottom surface of the liner's shoulder. The 'sharp corner-into-a-fillet' trick can't be used for this seal because it might have created inconsistencies in the heights of the shoulders and issues for the combustion chamber seals. Instead, the upper coolant seals rely upon a pair of smooth flat surfaces pressed together by the sandwiching forces of the head when torqued down to the cylinder block. The integrity of this seal can be affected by the parallel alignment of the liner inside the bore of the block since it affects the parallelism of the sealing surfaces. This alignment is influenced by the lower coolant jacket's compressed o-ring as well as the liner collar support hardware between the cylinder block and crankcase.

As far as I can tell from my research, the liners' coolant jackets in the full-size engine were similarly sealed. There were certainly plenty of documented problems with leaks, but evidently they were eventually solved. With the change to the liner's wall thickness that I've made, there is now sufficient space to add a -027 Viton o-ring as a back-up seal. With this modification, the combustion chamber becomes the only metal-to-metal seal. Adding this o-ring may increase the assembly difficulty involved with getting the liner into the cylinder block, though. Some very preliminary tests have shown the assembly may already be fairly difficult because of the need to compress and stuff the lower o-ring into the bottom end of the assembly. Before making a decision about using the upper o-ring, I'm going to machine the liners' lower support hardware and do some actual assembly testing using a single modified liner. I don't want the o-ring groove to become one of those mistakes that propagates through the entire batch of finished parts.

The last feature to be machined was a 60 degree chamfer that I added to the bottom ends of the liners. This chamfer will provide rod clearance near the bottoms of my thicker-walled liners, but more importantly it will hopefully ease the insertion of the ringed pistons into the liners. In the photos I've seen of the full-size engine's assembly, each entire cylinder block will have to be inserted down onto the crankcase over all six ringed pistons simultaneously. - Terry.

 

[kvom]

Does the crush height mean that once installed the liners are locked in permanently?

 

[mayhugh1]

kvom,
I used the term to just refer to the extra amount of height I will have for the soft edges of the counterbores to deform and seal against the liners when the heads are torqued down to the heads. The liners won't be locked in place. I do have questions about how many times this torque-down can be done, though, and I expect it would be unwise to exchange liner locations once it had been done the first time. I currently plan to assemble them only once, but s/n the liners so I can keep track of their original locations in case the heads have to come apart for some reason. In the full-size engine, I expect the liners on each bank were selected for uniform heights during assembly, and I plan to do the same thing. I recently read that these engines had an average actual combat time of only seven hours between rebuilds, but I don't know what was meant by a 'rebuild'. I suspect the liners weren't re-used in a major over haul if they could help it. - Terry

 

[Ken I]

Terry,
This as told to me by my father who worked on Merlins throughout the war.

In most cases a major rebuild went back to Rolls Royce and were downgraded for further use in MTB's etc that also used the engines.

Other than in-situ repairs, the engines if removed went back to Rolls and and invariably a new engine put in place.

The throttle on a Spitfire had an overboost position (I believe from 1 bar to 1.5 Bar) meant to be used in an emergency - to shake off a tail chase.
There was a "seal" - a red painted copper strip screwed across the throttle which you broke to get to overboost. If this seal was broken, then according to the "rules", the engine had to be removed and rebuilt. The pilot also had to explain why.

In practice they pushed through the seal on takeoff and used it as seen fit.
If ground crew asked a pilot to fill in the appropriate form explaining his actions, he would be told in no uncertain terms where to shove it.

On the other hand if an inspection revealed a broken seal, the ground crew would be up on a fizzer (charge).

The seal was a tightly controlled spares item - you couldn't get one without the required report forms.

Bureaucracy occurs even in wartime.

The solution to the problem was to get a local engineering company to make a press tool to make the seal - the aircrews paid for this out of their own pockets - completely off the books.

So after every flight they simply replaced the seals and the system was satisfied.

Apparently the ruse went undetected (or a blind eye was turned) for the entire war.

So it would appear that the Merlins received a great deal more "abuse" than officially recognised.

Regards,
Ken

 

[mayhugh1]

Ken,
Pretty cool story with rare perspective.
-Terry

 

[mayhugh1]

The lower ends of the coolant jackets are sealed with Viton o-rings that are sandwiched between pairs of supporting metal rings. These rings as well as the o-rings must be slipped onto the liners through the bottoms of the cylinder blocks. The upper liner ring bears against a shoulder that was previously machined into the liner near the bottom edge of the jacket. The lower liner collar is slipped onto the liner below its o-ring and helps keep the o-ring in place. The liner collars have flanges that will be captured between the cylinder block and crankcase when the two are assembled. These flanges must all be machined to an identical height in order to prevent crankcase oil leaks or, even worse, damage to the cylinder blocks during final assembly. The o-rings will be compressed 28% in the space available between the cylinder block and the cylinder liners, and so they don't require additional compression from the liner rings. Although it seemed excessive to me, according to the references I checked, 28% is about the right amount of compression for a .070" thick o-ring used for a static liquid seal.

When I originally decided to increase the liners' wall thicknesses, I thought I could integrate the upper liner ring into the wall of the liner, and this is what I indicated on an earlier assembly drawing. However, I had overlooked the fact that this ring had to be machined as a separate part because the liners have to be inserted through the top of the block during assembly, and the block's necked-down bore just below its top surface is too small to pass the rings.

The liner's shoulder for the upper ring is only .010" high and was previously turned with a sharp inside corner using a grooving tool. The liner ring that bears against it also had to be cleanly turned with sharp corners and a close slip fit to the liner in order to avoid assembly damage to the o-ring. In order to avoid scratching the liners or cylinder block during installation, these rings were turned from 6061. The aluminum blank, from which the rings were parted, was turned for close fits to the cylinder block's i.d. and the liner's o.d. A snug-fitting Delrin plug was temporarily inserted into the tailstock end of the blank. This plug allowed the rings to be cleanly parted without the burrs or ragged edge flashing that would typically be left behind if the parted rings been allowed to freely fall away. The plug also helped to reduce potential distortion of the fragile finished rings.

It's imperative that the o-rings be installed without damage because they will eventually become deeply embedded inside a complex assembly that should, for a number of reasons, be done only once. Working through the bottoms of the blocks to insert the o-rings into the tight spaces between the liners and cylinder block bores became an unexpected challenge. The o-rings wanted to be uniformly compressed radially before they could be slipped into place axially. I made a couple tools to help with their installation, including a ring compressor, but my results were hit-and-miss and typically ended up damaging the o-rings. During a couple days of frustrating attempts to come up with a process, scratching the cylinder block bores or the liners' shoulders, either of which could have resulted in coolant leaks, was a continual concern. I didn't remember having difficulties installing the o-ring'd liners in my Howell V-4, and after going back and reviewing the drawings I remembered that Jerry had used a groove depth for its o-rings that produced only 9% compression.

The eventual solution for my particular liners was to add an o.d. taper on the bottom end of each liner to provide an entrance ramp for the o-ring. During assembly, this ramp should convert a portion of the axial insertion force applied to the o-ring by its installation tool into a radially compressive component. The clearance chamfer that I had already added to the bottom i.d. of the liner, to ease piston ring insertion later on, left me with less space than I would have liked for the o.d. taper. It was also important to not leave a sharp edge on the bottom end of the liner that might also damage the o-ring. The space left available for the taper turned out to be barely enough. Since not even this area would have been available on the stock thin-wall liners, I'm not sure what a safe solution for them would have been. I continued using my three simple Delrin tools to practice a few trial assemblies, but tool #2, which was used to push the o-rings into the space between the liners and cylinder block was the only really important one.

Before assembly, the upper liner ring is dropped into the cylinder block bore, and tool #1 insures it rests squarely against the bottom surface of the block's deck. The bottom end of the liner is lubricated with oil and inserted through the top of the cylinder block. The liner ring is captured on the liner's shoulder as the liner is pushed through the block. When the end of the liner is within a half inch of the bottom of the block, a lubricated o-ring is set into the bore and backed up with tool #2. Tool #3, whose sole purpose is protect my hands from the liner's top sharp edges, is used to push the liner and o-ring against tool #2. This action hopefully forces the o-ring down the liner's entrance ramp and into the space between it and the block. Once the o-ring is below the bottom end of the liner, tool #2 is used to insure it is seated against the upper liner ring, and that the liner ring is seated against the liner's shoulder. A depth gage verifies the o-ring is at its proper depth below the liner's bottom end.

I was then left with the decision about whether or not to add an o-ring groove at the top of each liner for a back-up seal for the top coolant jacket. Without this o-ring, the top jacket seal will be just the originally intended .037" wide metal-to-metal seal between the bottom surface of the liner's shoulder and the top surface of the cylinder block. The use of sealant on these surfaces would likely result in inconsistent shoulder heights among the liners and create problems for the combustion chamber seals. There's only .001" clearance between upper neck of the cylinder block bore and the o.d. of the liner and very limited space for a ring compressor. I wasn't willing to reduce the metal-to-metal seal width at the top of the block for another o-ring entrance ramp. And, there is only .150" available for the .100" wide groove required for a .070" thick o-ring. Based on my experiences with the lower o-ring, I had already pretty much given up adding another one, but I turned an o-ring-grooved test part just in case. After playing with it for a short while, I abandoned the idea of a top o-ring entirely.

The final liner-related parts were the lower cylinder collars, and these were machined from 12L14. The o.d.'s are a close slip fit to the cylinder block bores, and the i.d.'s are close slip fits to the liners' o.d.'s. These collars control the alignment of the liners inside the cylinder blocks, and so they affect the parallelism of the mating surfaces that make up both the combustion chamber and top coolant jacket seals. The height of the lip that contacts the o-ring was selected to compress the o-ring only a few additional thousandths. The flanges on all the collars were ground to an identical height so the stresses on the blocks would be uniform after they are torqued down to the crankcase. Flats were milled on the sides of the collars to provide clearances to their neighbors.

Except for the lapping, the machining of the liners and the o-ring retaining hardware finally seems to be completed. - Terry

Errata... After posting, I noticed an error on the labels on the photo for the o-ring installation tools. The o.d. of tool #2 should have been labeled as being a close fit to the i.d. of the cylinder block bore instead of to the liner.

 

[petertha]

.... Although it seemed excessive to me, according to the references I checked, 28% is about the right amount of compression for a .070" thick o-ring used for a static liquid seal
.... I didn't remember having difficulties installing the o-ring'd liners in my Howell V-4, and after going back and reviewing the drawings I remembered that Jerry had used a groove depth for its o-rings that produced only 9% compression..

Interesting & timely. This might be what I've been struggling with on my radial crankcase face seal mockup. Just to make sure I understand, when you say 28% compression, would that correspond to a 0.050" groove depth? ex Compression = 1 - 0.050 / 0.070 = 0.28 (28%)

My 1mm section dia O-ring groove was prescribed with 0.7mm depth which would be 30%. This link for example recommends 0.8mm depth which would be 20%.
http://www.theoringstore.com/index.php?main_page=page&id=30&chapter=4

The other thing I noticed - this link for example shows an even 0.5mm incrementing section diameter progression. But the corresponding compression % is not a constant or trending up or down consistantly. Why would that be? Maybe just nominal dimensions or indirectly related to standardized tooling width?