Pelican Parts Forums - A Boring Job "line bore"

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Quote:

Originally Posted by PeteKz (Post 12078382)

How many miles on the engine? If under 200K, Don’t even split the case. Refresh the heads, maybe install a new cam, inspect and recondition the rockers, the top end back on and run the snot out of it. Save your time and money for an “ultimate rebuild”.

Too late for that Pete, shes down to single pieces.

I just finished the con-rod checks. Still round at 50ft-lbs, and at .010” stretch.

Quote:

Originally Posted by PeteKz (Post 12078382)

Thank you

The engine has 149k pluss (???) broken odometer.

Cam (964 Grind), follows, heads, oil pump, head studs, piston and cylinders are being addressed are all being addressed.

Quote:

Originally Posted by PeteKz (Post 12078275)

Porsche dude: this is for your ‘83 3.0 right? The aluminum 3.0 and 3.2 have proven to be very durable. Unlikely that machining is needed and unlikely that new main or conrod bearings are needed. Just check for free movement and Plastigage the bearings. You have read about the poor quality in some sets of Glyco bearings. If the originals are in tolerance I would keep keep running them. The magnesium cases are not as rigid, so if you have any doubts about the main bearing fit, getting that measured is a good idea.

There is an inherent advantage to continue using the bearings. They have already bedded-in together and demonstrated durability. In the olde days of “poured bearings” machine shops used to pour the lead into the steel or iron bearing saddles and then hand scrape them down to a little less than the desired tolerance. Then the engine operation would push the lead around a bit and smooth them out. Therefore it was better to leave good bearings alone than to rebuild them. Of course, modern shell bearings are made with much greater precision (well, they are supposed to be) and the Babbit surface is much thinner, although it still gives a little bit, but the principle still stands. Leave good bearings alone. You may introduce new problems by changing them.

Pete, when you rebuild, how do you check your main tunnel clearances? I've done maybe 20 now, (no where near as many as the experts!) and I've not come across a single case that measured within spec. ie, 3.0 case is meant to be 65.00-65.019mm... I'm finding they are all outside of that spec.. and sometimes the centre journals are up to 65.05mm...

Keen to compare findings...

As for re-using old bearings, I cannot bring myself to do that. Maybe I'm wasting money?

I haven't measured the tunnels on my small handful of Porsche builds. If there isn't any apparent wear in the bearing saddles (like embedding of the marks on the back of the bearing shells into the saddles), I don't see how they could be much different than when Porsche assembled them 40 years ago. Maybe they weren't in spec then?

On my last build (my current 3.2 into my 1973T), I used Plastigage. The case was a 1980RoW 3.0. I bought the crank and rods (a turbo 74.4) from Dick Elverud, and he had checked and polished it, so I knew it was straight. I installed the new main bearings, laid the crank into the bottom half, installed the top half, and torqued the case bolts to spec. After diassembling, the Plastigage showed right at .002" on all the mains. Close enough for me. That's the measurement you're really after anyway.

As for reusing bearings, I still like to use new bearings, even though I can't see that there is a benefit IF the old ones are in good condition and the plastigage measures within tolerance. Yeah, old habits, abundance of caution, etc. But with some poor Glyco bearings in circulation, Not to mention rising prices of high quality new ones, I'm somewhat more inclined to keep using original good ones now.

Important factor: I'm not a pro builder, having to warrant my engines to customers. I'm a heavy DIYer, so I'm willing to save money and time on things that I don't think make much difference. I didn't rebuild or buy new rockers and shafts either. They looked good enough to me. If I have to replace them at some point, I'm willing to do that. If I was giving a warranty, I'd rebuild or replace them too and just add it into the price to the customer.