New OS piston clearance

[gaspumpsam]

Have a set of new .040 OS pistons. ( finally found some at a reasonable price) can we use service manual clearance spec as gospel, or has someone found a different spec that is better, when we rebore.

[Lavoy]

Any good machine shop should bore to the piston, not the manual.
Lavoy

[gaspumpsam]

Tks

[gregjo1948]

Any good machine shop should bore to the piston, not the manual.
Lavoy

GOOD ANSWER!!!!

[Lavoy]

My machine shop will not bore til I hand them the piston going in the hole, even though they have bored tons of blocks for me.
Lavoy

[gaspumpsam]

Absolutely true. That is why I waited until I had new pistons in my hand, but if you take factory specs for reboring on a pre 1955 auto engine, and bore to that( ie- .001” per in of bore- clearance , sometimes find that is too tight. ) I just thought maybe someone on here has found over time that a “ looser spec” works better.
The same idea goes with honing a cyl wall( if it’s ok to use, ) or just put a new set of piston rings on a good piston, and install and run engine. Just a thought.

[gaspumpsam]

Forgot to make it clear that we don’t hone cyl walls, as long as cyl are good to use. Has anyone tryed this?

[gregjo1948]

Forgot to make it clear that we don’t hone cyl walls, as long as cyl are good to use. Has anyone tryed this?

Not sure what you're asking. I've honed many cylinders and used original pistons with new rings. Specs should tell how the rings should fit on the piston and in the cylinder. I believe you need to remove the "glaze" in order to seat the new rings properly. I always ream the ridge every time to keep from breaking the new top ring.

[Lavoy]

I have never heard of not honing cylinder walls, new or rebored. On old walls, if the piston comes out, a hone goes back in. On fresh bored engine, my shop bores them to within .005, then hones to correct size. They have been doing all of my engine work for over 30 years now and most of the race engines for quite a radius from here.
Lavoy

[gaspumpsam]

Yes, I remove top cyl “ridge” of carbon and metal before removing pistons, is easier and doesn’t break anything.

I can usually get a good conversation going when I mention about not honing cylinder walls that are good enough to reuse, without rebore ( rebore has automatic hone, as Lavoy pointed out)
I have rebuilt many engines, both gas and diesel, and can honestly say, I have not honed an engine cyl wall ( if it’s good enough to reuse ) of a gas or Diesel engine , liners or solid block, and as long as pistons and ring lands are good, for many, many years. I try for chrome rings ( if there is a choice of cast or chrome, chrome lasts longer) and have not had one problem of piston, rings or oil consumption problems.
Upon start up after rebuild, engines let out a little puff of blue( excess oil on everything from assembly) then drive it, don’t baby it, and all is good.

I know this is way “ outside the box” of any rebuild manual, but after the theory of why ( it is not my theory , it was found by the company I worked for for years, and I believed it and tried it, and it works, it saves customer and owners money, and head aches for the mechanic) more on this later.

I did get an early Birthday present yesterday, the owner of the machine shop that ground my crankshaft, said he had a new water pump for a JD. He wasn’t sure what model it was for, but had been there( ordered for a customer that didn’t take it, ) and sure enough it was for a 440 gas. Got it for $150 cdn.

[gaspumpsam]

Forgot to include , all of us old mechanics have either heard, or have done it ourselves, that those “dam chrome rings” used a new set and engine kept burning oil, until I removed them and installed a set of cast rings, engine burned oil for a few miles, usually around 500 miles , then engine finally quit burning oil.!
Makes a person wonder why ?

[Lavoy]

If chrome rings don't seat, I would blame it immediately on the hone job, or lack thereof. There has to be millions of chrome rings running just fine, so if a few guys have trouble with them, my bet is on installer error.
As far as honing and ringing any engine, but these Dubuque 2 cylinders in specific, I have never rebuilt one that had a square bore. The least they are tapered is .020, and more than just a few that would not clean up at .045, and we had to go to .090 to make sure the hole was square again.
Lavoy

[gaspumpsam]

Like I said, I can usually get a good discussion going on this topic!
No, it was not improper or bad installation of rings, or improper honing. After much and exhausting checking and analyzing the problem, what they found was the metal the liners was made of( cast iron of some kind) was work hardened by the heat and friction from the normal running of the engine, so when it came time for rebuild, they were honed, but the hardness was
- say .006” deep, the hone marks, or hash marks weren’t quite that deep, so the hash marks were still in the work hardened skin, or area, and when the chrome rings were installed( chrome rings are barrel shaped, not flat, so they have an initial relatively small contact area onto the cyl wall, the oil splashed onto wall from running, the oil would actually run up the small grooves of hash or hone marks, dragging oil to top of cyl where it was burnt, causing the blue smoke and burning oil.

They found the cast rings were softer than the work hardened, honed, cyl walls, so as the engine was run in, or broke in, the soft rings would actually polish the walls smooth( chrome rings are harder and won’t polish walls, or make them smooth, like cast would) so they thought “ why smooth in the first place”? They started to use the chrome rings again, without honing, and no oil burning problem!! When a cyl wall is bored, it cuts the work hardened portion out, as the hardened portion is relatively thin.

As I am not an engineer, I don’t know all the scientific terms of the metal hardening tests, and how they determined this, but the results I can, and have tried to explain, along with the time proven results.

So, I have not honed a good cyl wall since, and have not had any problems, using either cast or chrome rings.

[Lavoy]

Interesting, never heard of that before. I'll have to ask my guys what they do or use for rings next time I am in.
Lavoy

[gregjo1948]

I figure the rough(unsmooth of a honed cylinder is what I want. When the rings are "breaking in", they are smoothing the "rough" which matches exactly the rings with the cylinder. The chrome rings, being harder than cast, take longer to seat because they are harder material. Once the chrome rings get seated, the oil consumption(if any) and compression, at that point, will remain the same until the engine dies. Being hard as they are, the chrome doesn't really wear as much as cast. That's my story and I'm sticking to it. I've been wrong three times and I divorced all three.