318 Big End Shells

a100terry · Post by **a100terry** » Sat Mar 25, 17 9:31 pm

Hi all
I have a 318 which was running ok, all compressions were good and oil pressure at 2000rpm was 35psi

All was well, except I had a noise at around 2000rpm - traced it to the bottom end and found that one of the crank shaft bearings (big end shell) was lightly scored. (see pic). The crank is also very lightly marked.

How bad does the crank need to be before it needs a regrind? Could I get away with simply replacing the crank shaft bearings? This is not going drag racing - it's just an old camper.

Thanks - Terry

shovelheadrob · Post by **shovelheadrob** » Sun Mar 26, 17 7:17 am

The only way to be sure is to measure the crank journal with a micrometer, it looks like the bearing is back to the copper so it is well worn. You might get away with a clean up with fine emery cloth & new bearings but you should also check the big end of the rod for being out of round.

Pete · Post by **Pete** » Sun Mar 26, 17 10:45 am

The shell looks in very poor condition - is that a groove cut in it by debris? I cannot really tell.

As Rob says, you can only ever tell by careful measurement.

You may be able to :"Get away with it" with just new main and big end shells, but my first thoughts are that it needs a full rebuild.

Blue · Post by **Blue** » Sun Mar 26, 17 12:01 pm

You might get away with it, if you run your nail across the crank and it dosn't get caught on any of the grooves I'd risk just changing the bearings.

Carl · Post by **Carl** » Sun Mar 26, 17 4:29 pm

I would have it polished takes very little off, and get it checked to see if it is still in its tolerances, as the engine is out you have nothing to lose as the crank will be coming out for main bearings to be replaced anyway, you will gain peace of mind though. Might be a good idea to change the timing chain if its a bit on the lose side too.

billybob73 · Post by **billybob73** » Sun Mar 26, 17 7:21 pm

i have a 318 that was built but has a cracked block , the crank was fine could pull it out of motor if you needed it

a100terry · Post by **a100terry** » Sun Mar 26, 17 8:09 pm

Hi again all
Thanks for all your advice - very much appreciated. The shell I took out (see picc) has not got a +10 or +20 on it. I am taking it for granted that the crank has not been reground? I am therefore going to order standard size shells. Is this correct?
Terry

shovelheadrob · Post by **shovelheadrob** » Sun Mar 26, 17 8:26 pm

Should be standard, the only way to know for sure is to measure.

mad machs · Post by **mad machs** » Sun Mar 26, 17 9:20 pm

Blue wrote:You might get away with it, if you run your nail across the crank and it dosn't get caught on any of the grooves I'd risk just changing the bearings.

With blue on this one, you could tear the whole thing to bits, find a load of stuff that's close to tolerance & end up rebuilding the whole shebang...

or...

Bung a new shell in & give it a go.

Know what I'd do, especially it being a 318 in an A100/108 , I can relate to that

MilesnMiles · Post by **MilesnMiles** » Sun Mar 26, 17 9:55 pm

I'd generally go for a replacing the shells, but that crank looks scored to me. I'd do it right once.

Post by **MattH** » Tue Mar 28, 17 10:28 am

I had a noise, stripped all the bearings out, replaced them and found it was a cracked flex plate, so nothing to do with bearings at all!!

They do look a bit worn, so if it was me, i'd chuck a new set in after cleaning it a bit and see how you go. Â£30 for bearings is much better than engine out rebuild.

Check that flex plate though!

octanejunkie · Post by **octanejunkie** » Tue Mar 28, 17 2:46 pm

MattH wrote:I had a noise, stripped all the bearings out, replaced them and found it was a cracked flex plate, so nothing to do with bearings at all!!

They do look a bit worn, so if it was me, i'd chuck a new set in after cleaning it a bit and see how you go. Â£30 for bearings is much better than engine out rebuild.

Check that flex plate though!

I'm with that. Clean it all up and chuck some new shells in. See what happens. Its not like they're built to tight tolerances to begin with, and like you say, its performing light duty in a camper.
I'd give the crank a go over with some emery cloth beforehand though, to see how bad the scoring is.

a100terry · Post by **a100terry** » Thu Mar 30, 17 7:32 pm

Thanks all. Am going with the put some new shells in and see what happens advice. Any thoughts on what, if anything to coat the new shell surface with? The older books say to use fresh clean engine oil.

Carl · Post by **Carl** » Fri Mar 31, 17 8:01 pm

a100terry wrote:Thanks all. Am going with the put some new shells in and see what happens advice. Any thoughts on what, if anything to coat the new shell surface with? The older books say to use fresh clean engine oil.

You can but i prefere to use a good engine assembly lub such as this its much thicker and stickier..Clevite 77