Vega V twin Aero engine

[creast]

I can't wait to hear it run.

Me too!!

 

[creast]

Well, after managing to wreck one of the steel cylinders during my heat treating experiment to just case harden the bore only I decided to go a mre traditional route and re-make the pair from aluminium and propose to shrink the cast iron liner in place. Actually this means the cylinders will be 30% lighter so its no bad thing either.

 

[creast]

Progress is slow but I now have the liners fitted and scalloped out to clear the crank. Unfortunately I overlooked the fact that the aluminium finned sleeve, being now thicker to accomodate the liner, prevents the nuts fitting to the studs. This means I will have machine reliefs at the four stud positions. Oh well!

 

[creast]

After another short break away I have managed to get the pistons machined. The rings have also been turned and rubbed down flat at the expense of abrading away my finger tips! Next step is to split and heat treat them. In the meantime, I can now Loctite the cams in the correct position to the pistons at TDC etc.
The Brass spacer tube where the prop fits is just to allow me to turn the crank more easily and keeps the end float to a few thou.
As I only get fragments of work time on this project I think it may be Christmas by the time I get to finish it! So.. that's my deadline

 

[creast]

The piston rings have now been gapped and heat treated ready for final fitting. I made a few spares just in case of breakages.
I had intended to make the valves two piece using silver steel ground stock and a stainless head but in the end decided to have a go at one piece in free machining stainless 303.
I was pleasantly surpised how well it went, taking cuts down to near size progressively from right to left in 6mm long sections. No centre was used and the final diameter carefully polished to size.
Work is now starting on the heads and so far I have machined the seat face details ready for the top side milling.

 

[petertha]

Coming along very nice! Couple questions:

- the cylinder studs that are resident in your crankcase, are they basically socket set screws or chunks of fasteners/threaded rods? What thread size?

- when you drilled for them, are they right through into the internal chamber but stud elevation set & secured with locktite or similar? (reason I'm wondering is some plans I have that show as blind hole so figured maybe a concern with leakage or something if connected)

-on the head picture re the induction/exhaust port, what diameter is the port & what fastener size to be used on manifold flange 2 bolts? (I like this idea over threading for a big flange nut or similar, especially if its interrupted with fins).

- looks like valve seat is integral with head itself vs insert seat/guides?

 

[creast]

Hi Peter
The studs are M2.5 and proper studs i.e threaded then plain dia then threaded. Was tedious making them!So they bottom out on the plain diameter. I will use thread locking compound on then final assembly.
Not all are fitted as yet as they need some trimming. The holes go right through to the crankcase since being 4-stroke it doesn't really matter about air leaks (the case has a drain underneath anyway).
The exhaust/inlet ports are 5.5mm diameter close to the imperial size from the plans. I intend to studs here too but they are a bit twee at M2. If I did this engine again I would definitely change some of the features. I tried to avoid B.A threads but in some respects they work better.
The seat is indeed in the alloy head rather than a seperate seat or combined seat/guide. If I mess up maybe I will fit the latter.
Thanks for your interest.

Rich

 

[creast]

Well, I have now pretty much completed both heads and all they need is a bit of fettling to finish. Both have the guides fitted but I am now waiting for a reamer courtesy of Ebay to finish them.
Tonight I have wound the valve springs and have yet to dress the ends square.
I also have the boring task of making many studs to secure the cylinders and heads!

 

[petertha]

Looking good.

On the piston ring heat setting, did you follow Trimble type formulas for dimensions & gap size etc, or some other method?

Are any modifications required to a conventional glow plug, or basically just screw it into head as shown?

What was your valve spring recipe/winding procedure?

 

[creast]

Hi Peter,
For the piston rings I turned them to match the bores and then snap cut with side edge cutters and dressed the break with wet n dry paper.
I then spragged them open with a piece of scrap and clamped them flat betwen two large washers. The stack was then evenly heated with a blow torch to cherry red and allowed to cool naturally. This method seems to work but as yet I have not installed or run them. I still have to gap the rings to the cylinders.
The glow plug is a 4-stroke type and in fact I posted another query on HMEM to see if the recess was excessive despite being to drawing.
http://www.homemodelenginemachinist.com/showthread.php?t=23607

I used 24swg piano wire to make the springs. After trialling on various rods I settled for a 4mm rod which had a small hole drilled thro to anchor the wire for its first wrap. A tubular guider was placed in the toolpost of the lathe to direct the wire and the leadscrew was set for approx 2mm pitch. Turning the lathe by hand and maintaining tension, several close wound wraps were made before engaging the leadscrew. After sufficient turns, the leadscrew was disengaged and more close wraps added. The springs are then trimmed back to remove the excess coils and flat faced each end on a diamond disc. I did bake these at 130 deg C for an hour to stress relieve but I have since seen this should have been higher around 200 deg C.
They are not perfect but I think they will be fine.

 

[creast]

The heads are now pretty much complete and another trial assembly to check the rockers and valves. The springs feel pretty firm, more than I expected but they are close to the plans dimensions. My guess is they are about 1 to 1.5 lbf compressed. Next is the push rods and then the tricky fabrication of an inlet manifold as I have chosen to try it out first on a single carburettor from an R/C supplier.

 

[Syd]

Hi Creast. Looks to be a nice bit of machining, isn't it tiny! I'm intrigued by the overhung crank, how did you attach the camshaft? Looking forward to your next post.
Cheers, Syd.

 

[GailInNM]

That is a great looking engine. Very nicely executed.
Thm:Thm:
Gail in NM

 

[creast]

Thanks for the kind comments Gail & Syd.
Syd, the cams are gear driven by a rotary arm which is driven by the crank pin. Some of my earlier posts show the timing case. I have attached section view from the plans which may explain better.

 

[creast]

Tonight was spent lapping in the rings. I hadn't intended to but the plans say otherwise. Anyway the engine was feeling tight and although slightly less, still is.
The push rods are done and its getting close to try running. I am still struggling with the inlet manifold for the single carb which I feel is a quicker route to running but maybe I am wrong.
I just had to try the prop on to see how it looked and also make turning the engine over easier!

 

[James6605]

Beautiful work mate!! Can't wait for the video of the maiden run.

 

[necchiom]

Awesome! With compliment. When the first run?

 

[petertha]

Tonight was spent lapping in the rings. I hadn't intended to but the plans say otherwise.

Looking good! Care to elaborate on your liner & lapping procedure? (I'm info gathering on my cylinder trial/mockup).

- did you use a lapping tool & compound to dimension & condition the liner ID's?
- anything subsequent conditioning like those balled abrasive brush hones to give the criss-cross pattern?
- by 'lapping in the rings', do you mean rotating engine under low external power or..?
- I'm interested in the fit & machining of aluminum cylinder & sleeve. Is it a heat shrink fit, or sliding fit? Are the jugs just bored or also lapped?

 

[creast]

Well it has been some time since I posted. I had hoped to have completed this project by Christmas but alas not so.
I have been struggling to get any life out of the beast and my first suspicion was the compression. I have resorted to just trying to get one cylinder to run first and this has lead to me making a new piston with a tighter fit and virtually no ring gap. I have also just gone for one ring rather than the two rings in a single groove.
The cold weather does not help and with a bit of pre-heating the cylinder with a blow torch she did try to run a few times and then compression was down again.
It appears the inlet valve is not seating properly and despite re-lapping the seat I am still stuck with a pretty ornament.
I decided to leave it a couple of weeks and regain my composure over the seasonal break
My task now is to modify or make new the head to ensure seating is correct.
Peter,
The lapping was simply done with very fine metal polish with the rings on the piston and moved in and out the cylinder whilst rotating in the lathe. This was done until the ring showed uniform polishing around its periphery. Not sure this is the best way really, I am still learning myself. No other laps or hones were used.
The cylinder was bored approx 0.0015" undersize of the liner diameter and heated in an oven to 200 deg C before pressing the liner in which in fact pretty well fell in. My first try was to do it by hand but as soon as the liner touched the bore it chilled the cylinder enough to grab it so always use a press of some sort or be very sure and quick!
Not sure what you mean by 'jugs' ?

 

[petertha]

Good detail thanks. I know what you mean about the steel liner > aluminum cylinder near instant heat loss. Funny, I've rebuilt my RC engines a million times & never paid much attention until just recently. The external liner finish is actually very smooth & same goes for ID of aluminum crankcase. Looks like lapping type finish, even on the aluminum ID. I think this combination likely assists easy liner insertion & removal because any machining roughness is only going to be more 'grabby' going in & out. I put my crankcase in a 400-450 degF toaster oven. The liner rarely has much resistance, this is more for the bearing removal. It would be kind of a shame to sacrifice the aluminum cylinder with a permanent liner, hence the question.

'jugs' = vernacular for 'cylinders'. Maybe its a N-Am thing.
http://www.totalmotorcycle.com/dictionary/J.htm
There's another kind of jugs, but I wont go there!