here is a question for anyone that knows. I am getting ready to get back to work on my 406 and me and a friend of mine put it together. I was there for most of it but the one concern I have is I WASN'T there when he stuck in the rods and pistons. He has built a few motors and they turned out fine but he said when he stuck pistons in he never checked ring gap. they are speed pro hyperutectics and matching speed pro rings. he said he has never checked ring gap or bearing clearence. he said as long as machine shop did their job as long as torque is in spec it will work. He had all his machine work on his last motor (13.1 to 1 327 with .480/.480 cam) done at NAPA. I had mine done at Riverside Engines here in Tiffin, OH. So since mine was a reputable and expensive machine shop I should be OK hopefully. Should I be worried about this? or does anyone else go by this also?

 

most if not all hyper pistons require a larger than stock end gap. you need to file fit the rings and you need to check the end gap. it's foolish to think everything is going to be find just throwing the parts in without checking end gaps or clearances. i'd be finding me another engine builder.

 

so should I yank motor back out before I try startup and tear it all down again?

 

may just try it anyway sounds like it would be risky but I don't even have everything done but motor is basically complete and in there now and I really don't want to jerk it out and basically sart all over again. Myself I would think since the pistons and rings came from the same place they should be real close. by the time it is all said and done I will probably jerk it out anyway though not real sure but I don't wanna mess up $1200 worth of machine work. anybody get theirs done any cheaper? I didn't really get anything special done other than the center hone and decking other than that all normal stuff which those are both normal just not done at every rebuild.

 

It's a question of risk....

Ever seen what happens to a motor when there's not enough ring end-gap, and the ends butt when the rings heat up?

Let's just say, that when the outer diameter of the rings exceeds the inner diameter of the cylinder, they get REAL HARD to move up and down. Something always gives; usually the pistons. The top ring land blows off.

If they just barely touch, and keep moving, they score the cyl walls. Then you end up with mystery ring smoke and mystery blow-by. Another not-so-fun outcome.

On the other hand, it might be perfect.

There's no way to predict what's going to happen, without actually measuring the ring end-gap. Which it's a little late for that now.

How lucky do you feel today?

I don't measure my machine work by "cheaper", so I have no clue about that.

 

trust me definitely not a motor measured by cheaper but my problem was he has done his own so he must have known what he was doing but myself since this would have been my first complete motor build I would have checked everything for th esake of doing it. may tear down and rebuild it anyway.

 

when you come back and psot "why's my engine smoke" , "what happened to my engine", or "look at these pistons" referance this post or link to it just so we all have a frame of referance.

 

lol I get the point It will be done right. figured I better since he never checked bearing either. may just end up fixing this one or selling cheap or parting out and doing my 358 now. probably fix this one right and make sure i just do it myself this time that way I know it all gets done right.

 

That's probably a good idea. Even if you don't change anything, if everything checks out fine, you'll learn alot in the process.

Trying to predict whether it's OK or not, is alot like trying to answer the question "Do I have enough life insurance". There's only one way to get the final answer; and you only get one chance. Otherwise, it's all about risk, and trying to prepare, and doing it right so that there will be no error.

 

after some thought since I will already be tearing motor down again to check I may end up selling the rotating assembly and switching to billet and forged stuff for either nitrous or turbo. more than likely or may just do it for bullet proof bottom end street motor and make sure I do it all myself this time so I know it is done right.

 

Edit:

If the bore was honed to a diameter within spec, and they are NOT file fit rings, than the ring gaps should be within factory specs as long as the rings are designed for use with THE PISTON BEING USED.

OEM rings and OEM pistons require no fit filing as long as the bores are WITHIN SPECS. Some hyper pistons are sold with specific rings, and are designed as OEM replacements. Some forged pistons, such as TRW-2256 are also an OEM type piston.

However, If the bore is way small, or way large, you will be out of spec AND your piston to wall clearance will be off too. Thats why your engine builder said it would be fine IF THE BORES ARE WITHIN SPEC.


When are file-fit rings used?

Hyper pistons, and forged pistons have expansion rates (some high silicoln pistons expand very little like cast, other hyper pistons go NUTS when they get hot). If you are using hyper or forged pistons, with an off the shelf ring set you NEED to check the clearances.

File-fit rings are designed for application specific purposes. I.e, opening or closing ring gap based on motor specs, intended use, etc. You don't file-fit the rings to make up for poor cylinder hone diameter however, that is a mistake.

Regardless of all that however, the clearances should ALWAYS be checked as ede and sofaking said. But it's not just ring gap. It's side clearance, depth, rod side clearance,
crank end play, bearing clearances, etc. If you don't have all your clearances written down on a peice of paper, you didn't get what you paid for.


-- Joe