VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 235 rebuild downs & ups & downs

Sometimes, just when the end is in sight, it moves again.

I'm in the process of rebuilding a 235 for my '55, and ran into a problem back in September, when I found I had a cracked oil pump bracket. This was after spending a bunch of money to re-machine the block (see post 55 235 oil pump mounting problem ). With help from a friend + my son, that problem was solved nicely. I'll put some details of the solution on that original thread, since it's kind of interesting. It was a LOT of work though.

Having overcome that obstacle, I began yesterday to happily reassemble the engine. I cleaned everything up, set the crank in place, and began torquing the main bearing cap bolts. I got to the 3rd cap (the thrust bearing) and tightened the bolts in 20 ft-lb increments. I torqued one bolt from 80 to 100 ft-lb, then started on the other. As I pulled it tight, I noticed the torque go slightly soft. I stopped and found that the main bearing cap had broken!




You can see in the photo that the bolt hole wall thickness in the cap was noticeably thinner on the side that broke. There doesn't seem to have been any pre-existing crack. I don't know of anything that I did wrong. The bolts spun freely in the block, but weren't lubricated (which would have caused higher bolt tension for a given torque). I wonder whether the torque wrench (an older Snap-On click type) was reading too low, although it had been checked not long ago; I'll check it again. If anybody wants to point out something that might have contributed, I'd be glad to hear it.

The fact of the matter now is that now I have another big "challenge". The existing block + bearing caps had been line bored. Maybe it's possible to get a new cap and have a shop bore it to match the other bores, or just line bore the whole thing again. I'll have to talk to a shop about that. The fact that the problem bearing is the thrust bearing may complicate things. Does anybody know where I can get a replacement bearing cap?

Another obvious path would be to get another block. Does anybody out there know of a '55 235 block that might be available? I live near Lancaster PA. Any help in my hour of gloom would be appreciated.

Joe

Joe,

Although I might be the first to respond, I doubt I have the reason for the break.

I would assume that there was a high place that permited the cap to "rock" and thus have play on the broken side when you went to torque it down. How the high place occurred is beyond me since you had it line bored.

You should be able to get a new cap. Check it and find out if it will fid down flush before you torque it in place. I'll state the obvious something is wrong and you need to determine what it is or you're gonna bust another one.

Good luck with it.

Charlie

If I were to venture a guess it appears that the cap was cocked and not in the saddle in the block when you started to torque it down. I would try and find someone that has a main cap. I would think that a machine shop could align bore it to fit the one cap. I would have a discussion with them about how much material has been removed in the previous align bore job that was done. You don't want to get in a situation where the cam gear and crank gear mesh to tight because of lowering the center of the crankshaft by align boring the block.

I did some serious looking at my broken bearing cap & associated parts today, and found a little ring of cast iron encircling the bolt that was on the side of the cap that broke:



Looking for the origin of that little ring, I found that it matches the other hole on the same cap. In fact it fits in very precisely:



Look at that fit!



I think that the ring of iron broke away when the cap was removed, and stayed under the head of the bolt where I didn't notice it. When I assembled the bearing cap, this wedge-cross-section ring rode along on the bolt. When torque was applied to the bolt, the ring-wedge pushed the cap apart. If the bolt had had ended up on the other hole (where the ring originated), maybe nothing would have happened. (?)

From now on I'll be looking under the bolt heads!

Thanks for the comments about having something under the cap. I don't think that happened, but it's something to make extra sure about in the future.

Joe

I have some new 235 caps, but no longer labeled with part numbers.

If you can provide the stamping number or casting number of your broken cap, I can check to see if I have a match for you.

I put a post in the parts wanted section. I answered some questions & posted a photo to clarify the part description: part number 8837808 (maybe?), dowel type insert (not tang). The post is at 235 main bearing cap #3 needed. Chevgene says that I need a cap from a '53 Powerglide or 54-55 engine. Thanks for checking - I hope you have one!

Joe

One thing to keep in mind,I'm not sure if you have a timing chain,or gear to gear from the crank gear to the timing gear.When you line bore blocks too much,if you have a timing chain,it will become loose,due to moving the crankshaft towards the cam.In other words,the more you machine out the main bores,the closer the crank comes to the cam.If you have gear to gear type timing gears.the mesh between the gears will become tighter.Keep this in mind before making your final decision.

Joe,

This could have happened to anyone, so don't beat yourself up. It's a problem with no perfect solution.

An option that may be worth looking at is welding the broken off piece back on. Because the broken area is thin and small the heat input from stick welding would be so minimal that you would be able to pick the part up with your bare hand right after welding as long as you don't touch the weld area itself. So distortion may not occur at all.

There is a Harris stick welding electrode called "Super Missile Weld" that is ideal for this application. I have used it to fabricate and repair various cast iron parts. That electrode will weld any ferrous metal to itself or to any other ferrous metal (ie dissimilar metal welding). It's truly a miracle electrode even in the hands of an amateur welder like me.

Proper preparation of the weld area would be essential, cleaning the pieces,chamfering the edges to be welded and good welding technique ("close, hot and fast").

What do you have to lose in trying? Checking with plastigage after the repair would give you the answer whether proper clearances were maintained.

Essential would be restoring the proper contours to the area where the bolt head seats after the repair. That can be best accomplished with a surface grinder and verified with a dial test indicator. This welding and machining is not simple, quick or cheap unless you can do it yourself but neither are other alternatives.

If this were my problem I would try the repair before resorting to other more difficult and expensive alternatives. You seem like a do-it-yourselfer so why not give it a try?

I agree with brino. The damaged cap is repairable by welding but it takes some skill with the specialty electrodes. I am fortunate to have an older brother with 45 years of welding experience. He has repaired various cast parts for me including starter'snouts', exhaust manifolds, heads, and small engine parts. Best results come from pre-heating the part and practicing on similar 'junk' parts to ascertain the power level required. With all that money invested in the motor, paying a welding shop seems smart to me.

There are some particular problems with welding such a piece...One is chamfering cast iron tends to smear carbon into the weld surface ( cast iron is about 4% carbon ) another removal of all the oil...Not to mention pre and post heating to prevent a crack from appearing in the "Heat Affected Zone" ( right next to the weld )...I'd look for another cap first...I've had some luck with Nickel rod ( you can grind it smooth ) and even brazing...( but it tends to pull oil from the porosity of the part ) All said and done, it would be wise to check the part with a Liquid Penitrent Test to be sure you haven't ended with a crack in the HAZ, if you go with welding...Good Luck

My plan for now is to find another cap & try to make it work. The 1/2 round in the block is at the right location, since the block was line bored. I think the best thing would be to leave the block alone, and fuss with another cap to see if I can get the diameter, measured vertically, to the right dimension. I can change that dimension either through use of shims (if its too small) or precision grinding of the flats on the cap (if its too big).

The real issue will be finding a cap, but there has to be one out there somewhere. If you know of one, please let me know. There's more info about the specific part needed in the "parts wanted" section, here: 235 main bearing cap #3 needed.

Thanks for the helpful advise.

Joe

Another problem with welding is if it's not full penetration it could crack again...And there lies a problem...Any weld that get into the bore would have to be ground out...Welding cast iron with it's high amount of carbon will create a super hard weld...usually much to hard to machine in a conventional way...I might add that if and when you find your "cap" that they machine it with the rod attached...Indicate the rod side as from "center" and bore the cap side to spec's...Without the rod in place, the boring bar will "grab" as it enters the cut...Not a big deal...But we want "pretty"...Don't we..? After all this work...Besides they should recommend it...How else could you hold the part to be machined...? It has to be centered...Unless of course you get lucky and find one the proper size...Luck be with you....

Just re-read your comments...wasn't thinking you were using inserts...Think you will find what your looking for...Don't lose any sleep...Kevin

Joe, I went to my "parts area" this A.M., the new caps (3) that I own are of the later model tang design, not the dowel design. Sorry.

Please recheck that stamping number, I do not see anything beginning with an "8".

The casting number of the main bearing cap was 3701247 and part #3703492 up until June of 1956. At that time the casting number changed to 3836538 and the part # 3719502.

Some possible solutions if the proper cap can not be found.
Find a 1956-1962 tang type cap and drill a dowel hole OR find a proper size insert for a tang type and use the lower half of the insert only in the later cap.

There should be an old 1953-1955 block out there some where that would privide a cap.

I might just do that (convert a "tang" style cap or use a tanged insert) if I have to, but 1st, I'll wait a while to see what turns up.

Joe

Regarding those caps that you have for tanged inserts... If nothing turns up, I might come back to you for one of those - see Chevgene's suggestion below.

The number on my cap is just unreadable. It's possible that the 1st number is a 3, but I can't tell.

Joe

We are currently in the process of moving from North Ga to Hendersonville, NC.

All of my "Chevy stuff" is being handled by me and helpers, via U Haul, rather than with the moving company. Some tiny and not so tiny Chevy pieces, parts, etc. that I do not want broken, etc. are part of the U Haul loads.

Second U haul load was shipped Saturday, 1/3/2015 to Hendersonville. I am still residing in North GA.

If the need for the cap arises, advise me with advanced notice, so I can "pick the part" from my now NC stash of parts. Next trip to N.C. should be Saturday, 1/17.

As of 1/3, the Chevy parts and me are currently 175 miles from one another ... soon to be reunited, I hope, as we forge on to N.C.