Offenhauser 270 ???

[aonemarine]

Im trying to find a build thread of Ron's 270 offy so I can get a better understanding of it. I have ordered the book, but being impatient as I am ive been trying to find a build thread on this engine.
Anyone on here build one or know where to find a good build thread on it?

 

[johnl]

I have the book too. Ron includes many photos of his build process. I am currently working on a Hodgson radial. The Offy seems a bit more complex, but I am looking forward to working on it once the radial is done

 

[aonemarine]

I have the book too. Ron includes many photos of his build process. I am currently working on a Hodgson radial. The Offy seems a bit more complex, but I am looking forward to working on it once the radial is done

More complex than a radial?? I havent seen the drawings for either engine yet, but the though of building a radial scares the hell out of me... LOL

 

[johnl]

In my opinion the Hodgson radial has not been at all difficult to build so far. Just building nine single cylinders and putting them on a common crankcase. Detailed plans sure help. Time will tell.

 

[gmac]

It's not just a set of drawings. The book is a detailed build instruction manual. Yes the drawings are included but also details on building tooling, machining setups etc. are documented.

If I remember correctly there is a forum on Yahoo - but not very active. I didn't have much luck searching for build threads on the internet. Many were starts to a build but never continued.

Good luck - be the first to fully document an Offy build. Ron responds to emails so you have that resource going for you.

Cheers Garry

 

[aonemarine]

Many were starts to a build but never continued.

Yea, thats what I have been seeing as well. Looks like there is a guy in AU that finshed one. Havent seen many others.
Im not sure if I will be starting a build anytime soon (I still have my webster I need to finish first) But I do want to have a look see as a possible canidate for my first cnc machining project. Ive been woring on joining the yahoo group, but its becoming more of a pain in the rump to register than one would have ever though...

 

[aonemarine]

Just got the book in the mail and have been studying up a bit on it. I do have to question the main bearing set up. Is that how the origonal engine was made? Weird to say the least.
I can see why you feel the offy is more complex than the radial now. LOL

 

[deboom_j]

I've built most of the parts for the 270 Offy. Just need to make an ignition system, and some tubes/pipes. But I'm really debating about tearing the engine down and making some of the modifications I've been thinking about for the last few years. I've seen 2 other Offy's besides Ron Colonna's and my own at NAMES over the years. They are out there! And everyone who's built one has a list of improvements/modifications too!

I've thought of starting a thread here about the Offy since no one else has yet. I've heard about the yahoo group, but I've never tried to join, as I find yahoo groups to be very difficult to use/read/post. It seems very outdated to me. I prefer modern forums like HMEM and CNCZone, etc.

If I did start a thread it would be more about the improvements that can be made to the engine for the purposes of easier machining, easier assembly, greater reliability, etc, etc.

I agree with an earlier post, Ron Colonna's Offy book is a great resource for all miniature engine builders, even if you don't want to build an Offy. Alot of people come to this hobby from other professions besides machining, the book gives many detailed descriptions of machining engine components, rational for selecting materials, making special tools/jigs/fixtures, etc as they relate to miniature engines. The ideas in the book can be applied to almost anything. Although, I do find some of the suggested setups to be more tedious or complicated than they need to be (this probably has more to do with the tools Ron had at the time he wrote his book). If you have a DRO for example or a CNC mill, or previous machining experience, you will no doubt have your own ideas about how to machine the parts.

John

 

[aonemarine]

I've built most of the parts for the 270 Offy. Just need to make an ignition system, and some tubes/pipes. But I'm really debating about tearing the engine down and making some of the modifications I've been thinking about for the last few years. I've seen 2 other Offy's besides Ron Colonna's and my own at NAMES over the years. They are out there! And everyone who's built one has a list of improvements/modifications too!

I've thought of starting a thread here about the Offy since no one else has yet. I've heard about the yahoo group, but I've never tried to join, as I find yahoo groups to be very difficult to use/read/post. It seems very outdated to me. I prefer modern forums like HMEM and CNCZone, etc.

If I did start a thread it would be more about the improvements that can be made to the engine for the purposes of easier machining, easier assembly, greater reliability, etc, etc.

I agree with an earlier post, Ron Colonna's Offy book is a great resource for all miniature engine builders, even if you don't want to build an Offy. Alot of people come to this hobby from other professions besides machining, the book gives many detailed descriptions of machining engine components, rational for selecting materials, making special tools/jigs/fixtures, etc as they relate to miniature engines. The ideas in the book can be applied to almost anything. Although, I do find some of the suggested setups to be more tedious or complicated than they need to be (this probably has more to do with the tools Ron had at the time he wrote his book). If you have a DRO for example or a CNC mill, or previous machining experience, you will no doubt have your own ideas about how to machine the parts.

John

t would be great to see a build log on this engine. Might spark some more interest in people building it.
Funny thing is after just a quick glance at a few things I already started thinking of how to change things to make it easier to machine....:hDe:

 

[deboom_j]

I was typing my first post, while you made your last post!

Anyway, as far as the main bearings go, is this how the full size engine is assembled? Well, yes and no. The fullsize engine has a fully enclosed crankcase, as in no main caps, and everything slides in from the rear. How ever the full size main bearings are a different shape made of 2 pieces instead of 4, and are split horizontally, not vertically like in the miniature. This is a source great pain and head scratching! It's also an area I'm keen to improve. Fellow Offy builder Ron Clark has the idea, if he were to do it over, he'd split the crankcase in half horizontally, use conventional main bearing caps, and screw the two halves of the c'case together.

My solution is to make new 2 piece main bearings, and cut notches in the crank case so the the bearings can be assembled to the crank, and the assy can be slid into the c'case from the rear. This is how the full size engines were assembled (well the later turbo engines weren't, they didn't have the notches). Actually the fullsize bearings were an interference fit with the c'case, so the c'case needed to be heated with a torch first to make it expand so the bearings could slide in! I wouldn't go that far with a miniature engine!

Assembling the miniature Offy has been likened to building a ship in a bottle by many people!

John

 

[deboom_j]

I just googled Offenhauser Crankcase, and found this website:

http://www.hotrod.com/how-to/engine/1504-assembling-270ci-offenhauser-indycar-engine-step/

It has some good photos of the process. The only difference is the full size engine is big enough you can get your hands inside of it, on the miniature, you need to use tweezers!

You should also think about modifying the way the c'case/block/head is held together. I have a solution for this.

Also, give serious thought to making a one piece block and head. The miniatures are notorious for blowing head gaskets, as were the full size motors. Guess how they solved the gasket problems on the full size engines?!!! I plan to make a one piece block and head some day too.

John

 

[aonemarine]

Actually the fullsize bearings were an interference fit with the c'case, so the c'case needed to be heated with a torch first to make it expand so the bearings could slide in! I wouldn't go that far with a miniature engine!

Honestly thats exactly what i was thinking. Make some bearing bronze (hockey pucks) split in half and fitted to the crank that are turned to about a .001" interfearance fit, heat up the block, drop the crank and bearings in place, and allow to cool. Headed off to work, but taking the book with me so I can study up....

 

[petertha]

I've thought of starting a thread here about the Offy since no one else has yet.
John

You get my vote. I know its extra work, but super valuable for noobs like me.

One thing I wanted to ask, only because I recently posted a question about valve cages & valve seats. I glanced at the Offy plans for reference & maybe missed some machining info in write-up description, but seems to me it was in the order of 0.045" wide seat or so. It obviously runs, but in your own build or connections with others, were they adopting this distance or modifying it (thinner) in any way?

 

[deboom_j]

Honestly thats exactly what i was thinking. Make some bearing bronze (hockey pucks) split in half and fitted to the crank that are turned to about a .001" interfearance fit, heat up the block, drop the crank and bearings in place, and allow to cool.

My concern with doing that on the miniature is how easily can it be disassembled?

My plan is to machine a portion of the main bearing web to the diameter of the crankshaft bore (+0/-.0005), this should position the bearings accurately enough and be easy to assy/disassy. Also, where the plans say to machine the 4 cutouts with a .4 radius, I'm going machine that out to the same diameter as the rod clearance. That will eliminate the need for people to make that 6" long fly cutting tool. When I do this, I'll take some pics and post them.

 

[deboom_j]

I glanced at the Offy plans for reference & maybe missed some machining info in write-up description, but seems to me it was in the order of 0.045" wide seat or so. It obviously runs, but in your own build or connections with others, were they adopting this distance or modifying it (thinner) in any way?

The offy valve cages are .375" OD, .3125" ID, so that gives a wall thickness of .03125". You're right, if the angle is 45 deg, then according to Pythagoras, the hypotenuse is about .044". I followed the drawings here, and as far as I know so has everyone else.

I think I did see your thread asking about the width of contact, honestly I don't have the experience to say, well you need this much or that much. I would be concerned about making it too small (say .010 to .015) as the valve may "hammer" it and compromise its ability to seal, and change the valve lash. Although, on our miniature engines we're lucky because the valves have significantly less mass than the full size counterparts, so maybe the "hammering" effect won't matter so much???

 

[aonemarine]

Yea, i can see the ship in the bottle now very clearly....

 

[deboom_j]

Well, just to prove there are people who have actually built Offys, here's a pic from NAMES 2015 (photo courtesy of Ron Clark).

From left to right: Julian Morrison from TN, Ron Clark from IN, Ron Colonna from PA, and John DeBoom from IA.

As I said before, Offys are kind of few and far between, but they are out there. Only 2 of the engines were in running order at the show (Clark's and Colonna's), but Julian's engine has run, just not at the show. And well mine's been 80-90% done for the past five years, or so.

John

 

[aonemarine]

Im on vacation this week and had plans on modeling the engine in cad then cam, but so far i havent even turned on the lap top. The campfire has been keeping my attention until its time for lights out so far, but i do hope to get on it soon.
Im still not sure about starting a build though. I like the engine, but im uncertain it will hold my attention long enough to complete the build. Time will tell i guess..