VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Boring a 194

How far over standard can a 1931,194 engine be bored? When I restored mine it was already .60 over. When it was rebuilt I just had the cylenders honed out because there was no ware ridge at the top end. I reused the castiron pistons and always thought that I have had piston slap. Well now I have the head off because of a blown head gasket and I checked the clearance with the pistons at top. There is close to .10", so do I pull the engine and bite the bullet or put it back together. There is a little over 4700 miles on the rebuild.

Hi Sal

I know this is not a 194 but maybe it will help. I recently pulled a 207 (1933) apart and it had .080" over pistons in it. I personal think that's a little big but they were getting away with it. I just had a 207 (1933) sleeved and it wasn't very expensive, now I have a fresh uniform wall thickness in each bore and don't have to worry about thin spots. I have had a few engines re-sleeved over the years and have never had any issues with any of them. The only thing I would make sure that the machinist do is at the bottom of the sleeve, have them step the sleeve and not a straight trough bore. That way the sleeve will not move up or down. It's a press fit but it assures that it says in place. Just a thought

Thanks for the reply Dale. I could check around and get an idea of cost for sleeving it.

I prefer not going over .060". Beyond that the cylinders get a little thin. But, it is all a matter of preference. Some dudes go to .080" over and don't give it a second thought.

With only 4,700 miles on your engine rebuild it is a shame that the machinist didn't address the oversize and wear issue on the cylinders when the engine was being rebuilt the first time.

By the way, any idea as to what caused the blown head gasket?

If the engine was running good before the head gasket problem I would put it back together the way it is. Like JYD I would be curious as to why the head gasket failed. I think with the cast iron pistons it will be a little louder than if you had aluminum ones.

I went on the 4-6 cyl tour up in the Ca gold country. While on that trip the tours that we went on were pretty steep and I was down shifting a lot. Well since I rebuilt the engine and installed a new honeycomb radiator the car has never heated up on me even in parades. Well between the warm weather and the hills it really got hot. On the trip back to the hotel the first day we started up an incline that someone thought was a 12 percent grade,I shifted from 2nd to 1st and got 3/4s of the way up and the car just died. I let everyone go by and I backed down to a turn around place and drove back a different way. That is when it started to loose power. The next day every a little hill I would have to down shift to make it up. I limpted back to the hotel and into the trailer with some effort. When I got home and checked the compression it was all over the place. 85 psi in 1&6, 45in 2,3&5, 30 in 4. So when I pulled the head it was blown between 2&3,and 4&5, so I was running on two cylinders. So I think that it was the over heating that caused the problem as far as I can tell. I am open to any other ideas.

Sal
I know you are getting the head done fully again so I wont go any further there. Like JYD I would not recommend going more than .060 in the bore and .010 piston clearance does sound to be on the absolute limit for alloy pistons but cast iron could be different. If all is fine otherwise and the lower part of the engine still in the car I would probably leave it alone for now and start collecting the rebuild parts ready for when it does become a major problem.

Like Dale suggested if you do resleeve definitely use the stepped sleeves, they dont move. The resleeving process will make sure the top of the block is straight as well. Resleeving is a total strip down process.

Tony

What type of headgasket were you using?

The clearance at the top of the piston is not a concern. clearance is measured at the bottom of the skirt.
I raced a 250 back in the 70s and it was bored .125 over with 327 pistons. Casting was thinwall on them. Never had a problem with overheating or anything else.

Did you retorque the head bolts after the rebuild? I found on my 32 that some of the bolts had become loose after a few hundred miles. It's possible that the old bolts are stretching from reuse and age and perhaps new ones would be more dependable for keeping the torque setting. Like you I also had a new honeycomb radiator after rebuild and it cooled fine but when it did overheat I found some bolts had gone from 70-75 ftlbs to 45-55.I did retorque and it cured the problem, but in hindsight I think changing all the headbolts would have been wise.

Skip, I had the copper head gasket on when it went and will put another one on when I rebuild. Thanks for all the information everyone. When I took it apart the head bolts were not that tight to get off, so maybe the overheating had something to do with it.

There are several 194 cu. in. engines running with piston bores over 0.060". It is normally not a problem as you have enough block thickness to got to ~ 0.125". Because the blocks might have voids it can get iffy to go too far.

Most head gasket failures are due to slight warp on head or block. Another common failure is using a fiber head gasket without metal between cylinders. I like the copper clad gaskets best but the steel clad are okay. Fiber is forecast for failure.

I have never seen pistons bigger than .060 oversize. Where would you get pistons and rings .080 or larger?

I have several sets of Semi pistons. They are ~ 0.080" oversize and need to be fitted to the bore. A friend honed his '31 block that was previously bored 0.060" oversize and had wear on top of that. He fitted a set of Semi pistons. Car has run many many miles with that engine.

Chipper - What are semi-pistons? Gene

They are oversize that is not completely finished. It is necessary to finish the outside by turning them in a lathe and then cutting the piston pin sides an additional 0.002". Or a machine shop can cam grind them to what ever size is needed. They are the best option for engines that are already 0.060" oversized.

My Uncle has a 31 which is .080 over size and it is running great....not many miles yet, car needs to be finish one of these days.

Also to the head gasket, that is what happen to my 32 roadster. I rebuilt the head to fix some issues and no one told me about re-torqueing the head bolts. After about 700 or 800 miles I was losing power and just not running like I wanted. Then I was over heating all of a sudden, like overnight. Turns out the bolts all backed off and I had water in the oil after long...blown head gasket. The only thing that I will be changing now is putting back the thermostat because I can't keep the car cool when idling after running hard. But once I get moving it's way too cold.

The head is coming together. I got the new valve guides in the mail yesterday and they are at the machine shop. When I got there he was milling the head to true it up.So maybe next week I can start rebuilding. I will be sure to make a note to myself to re-torque the head. But you would have thought that the gasket would have gone sooner in that 4700 miles. At least it wasn't out on the road some place.

Just a thought.Before putting the head back on the block,try using a thin coating of industrial silver frost paint on the block face,wait til it just goes touch dry,place the head gasket on the block(a couple of guide studs come in real handy here),then paint a thin coat of the silver frost paint on the head face of the gasket,let it just go touch dry,then put the head on.
Torque you head bolts down,then after you've run it for a while,re-torque the head bolts,check valve clearance etc.The silver frost will seal up any voids between the head gasket faces to both block & head.
I've used this trick on good 2nd hand gaskets to get me out of trouble over the years.Just food for thought.

The metal (copper)(steel) head gaskets can be used up to 5 times if not damaged, on the 4-cylinders.

A friend of mine memtioned that he sprays the head gasket on both sides with copper paint. Sounds like the same thing. I can give it a try, it will not cost much to do it.

There is a special copper spray for head gaskets that you can purchase in the auto parts store. I have used it and the stuff works great!!

Hi Sal. Glad you are getting your head staighened out. Just a thought. There is a good description of how to measure bore diameter and taper and the importance of getting it sraight under 32-36 catagory, " '36 207 ring job, by DFC ". Even though your pistons are still in the bores it might be a good opportunity to check them out. I know you have nothing else to do?? Gene.

Find a machine shop that can sonic test the block. They will be able to tell you how thick the walls are and if it is safe to bore it any further. We sonic test all antique blocks for safetys sake.

Melissa
www.earlsmachine.com
Seattle, WA.

Hi Melissa, and welcome to the Chevy chat site. That sounds like a good thing to do for the older engines that have already been bored out. Thanks for the information.