BC

Measuring. The crank does not seem to wear much unless there is a real problem. I am not suggesting reusing the mains, just that new mains of std size will normally work fine. Just pay close attention to clearances. The tools (it has taken me years to acquire the right tools) are the expensive part here.

69gaugeman

Just to clarify, the tools to measure the mains not the tools to do the mains.

Andrew, We just did this for Livio's engine. When you get there we can help. Plastigauge is sufficient to confirm clearance if there was no damage to the crank itself.

We polish plain bearing journals in some of the plants I am in, so if you want some proper polishing paper let me know and I will get it over to Rob Budd's for you.

AO

I ordered my plastigauges today. So in prep... do I measure against the exiting mains or do I get new ones and measure against that?

I'm off to remove the keepers on the second head... Back later.

BC

Correct. I think everyone is keeping up. The OP is smart cookie.

69gaugeman

With the new bearings. Make sure they are dry and clean.

69gaugeman

Post pictures of the existing mains and the crank when you get it out. Then we can armchair diagnose for you.

AO

Got the heads disassembled. All keepers, springs, shims, valves are out and accounted for. Also pulled all the old valve stem seals... That sucks BTW... They are a pain to get out.

Tomorrow or whenever, I will setup to measure valve guide wear to see if there is need for new guides or not.

Pics...

Rob Edwards

Why am I mentally picturing a martini glass of Amsoil with a couple of those valve stem seals sprinkled in like olives?

ThetaTau87

As 69gaugeman said make sure they are dry and clean, but also be careful not to allow the crank to rotate at all when installing and removing the bearing shells. Any rotation of the crank will smear the plastigauge and ruin the measurement.

Rob Edwards

Does anyone know anybody that ever rebuilt a 928 engine and didn't end up using the standard 928 101 901 07 main bearings? Anyone seen a crank with a main bearing journal worn below 69.971 mm? I'm sure it has happened, but even the 100K mile, regularly tracked GTS crank that I nearly killed by running the 2/6 rods dry had main journals that measured as new.

daveo90s4

Hi Andrew,

At post 97 you show your valves all standing nicely beside one another, behaving themselves, not yet fallen over in a heap and mixing themselves up so you'll never be able to get the same valve back into the same hole (which you will want to do if the valve guides don't need replacing). How about poking them through some cardboard and number them to avoid a headache later on?

Cheers

Dave

FBIII

Your timing on undertaking the task seems spot on. The first set of exhaust valve seats pictured are in need of a regrind.

69gaugeman

Although this is the preferred method, I have re-lapped valves that had gotten mixed up and not had any problem. But by the looks of things a seat grind is in order. Not sure grinding the valves are worth it though, as new ones are 12 and 18$.


Agree.

Cheburator

Heavily tracked GT motor with 100k, then a rebuilt, then another 40k of very hard driving, including track driving and racing - still bang on in the middle of the factory specified tolerance according to the plastigauge

Brand new GTS crank raced for 30hrs, then the engine was starved of oil until the 2/6 practically welded itself to the crank, 2/6 rods bent into a S shape, yet zero wear on the mains...

daveo90s4

Re lapping in valves, yes valve seats need to be redone. But I'd think that is a given, would be penny wise pound foolish to get this far and not do that. I'm sure Andrew had planned to do so anyway, new valves or not. (yes Andrew?)