New Pistons but.....what bore?

R

Rparker28

Senior Member
All- decided to get all new Pistons for my 29. Should I just stick with the standard bore? Also.....should I get new rods? Ralph
 
What sized pistons are in it now?
Does it need a rebore? If so, by how much?
Is there a step at the top of the bore? If so, how much?
Cylinders usually wear to a barrel shape. What is the maximum diameter? (Usually about 1/2 way down)
Why do you think you need to replace them?
In short, we need more info.
 
In short.....the engine was originally stuck. Got it unstuck last week but unfortunately the piston in cylinder one did not fair so well. It is at the top of the cylinder and I am unsure if the top of the cylinder broke off or the rod came off. Talked to a guy today who said he would rebuild and I was just curious if I could replace the one piston or would it be better to replace them all since it would be apart. A lot of unknowns on that one cylinder. Ralph
 
one piston has been replaced since the car was invented and ran many many miles. This rebuilder of yours - does he specialize in model A engines?

but yes it needs to be checked to see if they are anywhere near standard or it needs to be bored out to the next size up. If that is the case then yes all 4 must be replaced.
 
Ralph, patience is your friend. Let the engine guy have a good look at it. He will measure all the cylinder bores and the pistons. If you are lucky you may only need to replace one piston. Or maybe just one connecting rod let go. Good luck. Keep us posted. Jeff
 
MAKE SURE he knows model a engines. If he don't he can do more damage then is already done. If he has ask him what he has done to engines in the past. There a simple engine if you know what your doing. If you have a friend that knows model a engine see if he will go with you.
 
Thanks Jeff........He said I would have to take the engine out and bring it to him and that it would take about 6 weeks because of his workload. He has done engines for show cars and such and has a good reputation. I just want to get the car on the road and I get ahead of myself sometimes. Is it difficult to get the engine out of the car? Ralph
 
I can only assume that you have checked him out in the archives, here and on HAMB? Why don't you post his name and see if anyone recognizes him, if no one recognizes him that may be a bad sign.

Charlie Stephens
 
You can pull that engine by yourself Ralph. Everything is nuts and bolts....
You and your car are going to be doing alot of bonding, and getting to know each other on an entirely new level. I pulled the engine out of one my cars just a few weeks ago. Took me 4 hours by myself. The guys here on the forum are all here to help. Keep us in the loop. Jeff
 
Rparker28 said:
Thanks Jeff........He said I would have to take the engine out and bring it to him and that it would take about 6 weeks because of his workload. He has done engines for show cars and such and has a good reputation. I just want to get the car on the road and I get ahead of myself sometimes. Is it difficult to get the engine out of the car? Ralph
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No, It's not particularly difficult but that largely depends on your ability. You will need a hoist and a clear area in which to work. If you are taking the engine to him, I'd suggest some kind of a stand to hold it while you transport it.
Is there another Model Aer in your area you might be able to ask for assistance? Your club, maybe?
It sounds as though you have not done much of this in the past. For your engine guy to work on it, you will have to remove all of the ancillary items, generator, manifolds, starter, water pump etc etc. You will also have to reinstall them. I suggest for your own peace of mind that you photograph everything as it comes apart so you can see how it goes back together. If you're anything like me, you won't remember everything. A few digital pics cost nothing and can save lots of stress.
I'm sure if you run into trouble, there will be plenty of help here.
 
Hey RParker, have you worked on an engine before? If you have some experience, there is a lot you can do your self. If the babbit in the rods and mains is good, you might get away with replacing the one piston. Engines this old have usually been bored out to a larger size, you won't know until the head is removed. Most of the time there will be a number stamped on top of the piston indicating the "Over-bore".
 
Thanks to all for the advice and encouragement. I am going to tackle it and if I get in trouble then I know where to come to. I have already done work on this car that I never thought I could do. Repacked the wheel bearings Sunday!
 
Rparker28 said:
In short.....the engine was originally stuck. Got it unstuck last week but unfortunately the piston in cylinder one did not fair so well. It is at the top of the cylinder and I am unsure if the top of the cylinder broke off or the rod came off. Talked to a guy today who said he would rebuild and I was just curious if I could replace the one piston or would it be better to replace them all since it would be apart. A lot of unknowns on that one cylinder. Ralph
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If the engine was well stuck, it's likely there is a groove around at least one bore where the rings have been sitting. Wait till your engine guy looks at it but I'd be preparing for a rebore. It's also possible there will be a groove corroded into one or more of the crankshaft journals where the cap and block (or rod) meet. If that is so, don't get upset. Ignore it/them. They will not cause a problem - the crankshaft should never come into direct contact with the babbit. There should be a layer of oil between them.
I have a crankshaft that has never been ground but has such a groove on one main journal. I will one day, add counterweights and use it. The groove will act as an oil reservoir.
 
Rparker28 said:
Thanks to all for the advice and encouragement. I am going to tackle it and if I get in trouble then I know where to come to. I have already done work on this car that I never thought I could do. Repacked the wheel bearings Sunday!
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Good for you!

You will learn.

Get Les Andrew's book if you don't already have it...

http://www.mikes-afordable.com/product/A91024A.html

Find a Model A or any antique car(or even tractor) club nearby and see who rebuilds their engines...

Maybe one of these clubs is nearby?

http://www.mafca.com/chapters/GA.html
 
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Chances the pistons are not standard. I have disassembled LOTS of Model A engines and not found but a very few with standard pistons and those were sleeved. The advice to use someone with Model A/T experience is good to take heed of. I get lots of engines in that machine shops claim to be able to rebuild till they find out they are totally ignorant of the workings of the babbitt engines. Be careful and have fun.
 
I don't know if you are aware of it or not. James Rogers comes with excellent credentials as rebuilder of model A engines. There are several though out the country, but he's the closest.
Terry
 
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