The Stovebolt Site Forums The Shop Area Engine Shop ENGINE CRANKSHAFT MAIN BEARING TORQUE?

The 216 in my 41 is leaking oil out the rear main seal. The machineshop used a neoprene seal and the surface of the crankshaft is a little rough so it leaks. I am installing a new roap seal (provided by the machineshop at no cost to me). So I am installing the seal and need tightening torque for the main bolts. My 1941 chevrolet service manual dosn't give a torque spec. for the main cap bolts. It only said to tighten the cap bolts and if it the crankshaft bound up then add a shim and check it again. NO TORQUE SPEC GIVEN. NO TORQUE SPEC. PAGE IN MANUAL. HUMMMMM!?!? HOW TIGHT IS TIGHT?

I think the torque is 125 ft lbs. I'll check, but I'm sure someone else will have the answer. In order to install the rope seal, you should loosen all the main caps so the crankshaft can be pulled down a little to loosen the fit. Installing those seals has been described several times at this site, so if you search the site, you will find quite a bit of information on the topic.

It helps to remove the spark plugs so you can rotate the crankshaft easily to help pull the seal into place.

Harvester

Thanks for the reply, I am no stranger to installation of a roap seal. I just could not find a torque spec for the main cap bolts.
Most main cap bolts I have tightened are closer to 85 ft. lbs. But I have never dealt with a shimmed bearing cap before.

No no, the torque is not 125 ft lbs. For 1947 it is 100 to 110 ft lbs. In 1948 they made changes to the crankshaft etc. but I believe the torque remained the same. I think yours should be similar or the same.

Thanks truckernix that sounds much better to me. But as I said I have never dealt with shimed bearing caps before so 125 sounded good also. I think i'll go with 105 and split the differance.

so, you'll have a neoprene 'block' seal and a rope cap seal? or do you plan to pull/replace the block seal also?

The engine was o/h about 2 years ago and has only been run about 3 total hours. The machine shop had put in red neoprene seals, (upper and lower) and it was leaking. I removed both upper and lower neoprene seals and am going to replace them with rope seals.

I think he is going to replace the neoprene seal top and bottom with the rope type.

Toyvo,
Best gasket makes a seal that is a new product. It is a woven teflon seal and many people are impressed with it. If you want to go NOS, I know of a source if you need one. Many think that the new non asbestos seals are not up to par.

The secret for me in getting a good seal on the crank was to adjust all the main bearings to minimum clearances. Once I did that the new seal worked perfectly. As you probably know a neoprene seal will not work on the old 216.

truckernix, I did not know that the neoprene seals would not work. The machine shop that did my o/h put them in. I assumed they had done this before as they were well versed in the o/h of older style engines. In fact the owner had special jigs he made 30 years ago to bore out the rod babbet and install half shell bearings in the rods. He also had the tool for aligning the oil pan squirters so that they were squirting on the right spots on the crank. He was pumped up at getting to use them again. I only wish I had researched the installation of the neoprene seal install before I had the engine back from the machine shop. Live and learn.

The seal groove on a 216 is deeper than a full pressure 235, so the neoprene seal is not held tight against the crank.

Thanks Dave. Wish I had known that before the engine was in the truck. Now I am dealing with drippy sh--!!!!!!!!

I just checked all of my oil clearances on my main caps with plastigage, using 100 ft-lbs torque. Now that I installed the rear main seal and torqued the main caps for assembly, again to 100 ft-bs, I can't turn the crankshaft by hand. It seems like this is too tight because I was able to turn it over easily prior to disassembly. Did I torque it too much? I used a rope-type rear main oil seal. Is this normal?

It's not uncommon to get a stiff-turning shaft when the rope seal is first installed. It will loosen up somewhat as it runs. As long as the starter will spin the engine without excessive current draw, you're probably OK. Given these old engines' tendency to leak, a slightly tight new seal is probably a good thing!
Jerry