Question for those with engine building experience.

tooslow · Apr 2, 2008

I have a friend who is pulled apart an old 302 to rebuild. he asked a couple questions that i just don't know the answers to, so i'm asking.

He said the cylinder walls, journals, and piston skirts all look ok and he wanted to know if the standard connecting rod and main bearings would be ok to use. I'm assuming he isn't having any machine work done, so i'd think standard sized bearing swould be the right ones.

Also wants to know if he should change both timing chain gears since he is changing the chain. i would think its just a safe bet to do so.

Lastly, the part i'm really here to ask: what is the plastigage measurement or torgue specs for the rod and main bearings?

He's just doing a standard rebuild to get a few more miles out of it till he can get his new motor.

Mr. OAM · Apr 3, 2008

It would be a good idea to measure the journals on the crank with a micrometer just to be sure there isn't some odd wear on them and to check that they are still round. He should also measure the piston pins and pin bores.

Plastigage clearance is usually around .0015" - .0020". If the journals are still at spec then stock bearings will be fine. Otherwise, with such a small amount of clearance it doesn't take much before you need to look for oversized bearings.

Was the engine ever hurt or make any noise? If not and it is just a maintenance rebuild you should have no problems.

I don't have torque specs at the moment but that tells me that your friend should get a repair manual for his car. If you are going to do your own work it is worth it's weight in gold.

ALWAYS change both timing gears when replacing the timing chain. It's kinda like a new flat tappet camshaft and new lifters. You don't ever re-use the old lifters. The gears and chain are typically sold as a set anyways. Best to get a double roller.

Even if he is not going to get any machine work done he should hone the cylinders. They are likely to be glazed and this will not let the new pistons rings break in correctly.

Steve

tooslow · Apr 3, 2008

his car, is a 30's era "rat rod" pickup. i don't think there is an owners manual. haha

thanks though, i appreciate the help. i'm sure a 5.0 stang manual could help with the engine internally at least though. i'll advise him to pick something up to double check.

tooslow · Apr 3, 2008

instead of trying to retell everything in my own words, here is his exact msg he sent to me. with all details i know at this point.

"i just pulled my motor out of my rat rod,, cause the c4 trany went and figured i would do the leakin rear main seal. dropped the pan and screen was clogged with gunk, and brkt for pick up tube snapped and the back 4 connecting rod caps /bearings had lots of play, and ,i dont know how this timing chain did not skip or jump a tooth? so much play! anyways before i throw a 4 bolt 74 350ci chevy and trany into my 38 ford pick up rat rod , i guess i will have the tranny redone with a shift kit, and do the lower end on the engine with a timming chain. i really dont think the journals are scored up , and the cyl walls looked clean, pistons still have cross hatch pattern on skirts of pistons. do you think by putting standard connecting rod bearings, and the crank main bearings in with a timing chain is ok to do? i think it should be ok, i will also thro umbrella valve seals on the valves. this is probably the least expensive way of getting the most mileage out of a tired rat rod motor.. any idea what the plastigage measurement or torgue spec are for the rod and nmain bearings are ?
should i also get both timing gears with the chain?
thanks Poppa D."

Mr. OAM · Apr 6, 2008

After he gets the engine apart and can inspect the bearings he'll have a better idea of where he stands. It's still best to measure the journals with a micrometer to know for sure.

Steve