Bore Distortion

[mtrehy]

Hi,

I'm interested in peoples thoughts about a block that I have been looking at. It's an oddball part-complete restoration project from a deceased estate. The deceased previous owner was a bit of a hoarder and also a significant tinkerer.

It's an american V8 (original bore 3.5625"). The engine was part assembled and has had a big overbore and new (3.72") Ross pistons & rods, some professionally ported big valve heads, reground crank, new cam etc. Clearly the engine has not been run since these new parts were installed. Anyhow, I didn't want to trust it was put together correctly so pulled the heads and sump off to give things a bit of a check over. Bores look ok at a glance - some honing marks are visible but checking with mercer bore mic shows what I assume is ok running clearance side to side (around 0.003" +- 0.0005 on all 8). Strange thing is though that I am getting consistent measurements front to back between 0.008-0.009.

I have a couple of other blocks which I think are unmolested so will be sorting out one of those but would be keen to know what could cause such a big variation - I assume this block was bored to match these new pistons and as the pistons have never been run I would guess that it must have left someones machine shop like this. I'm not sure how this would even be possible.

It seems very odd that someone has spent a vast sum of money on rods, pistons, heads etc but ended up with such a messy block. There were 2 large gouges in the block face between 1&3 and 5&7 that I can only assume were caused by someone levering off a head with 2 pry bars at some point.

Any ideas anyone?

Cheers.

[Boosted LS1]

Try again with the block rotated at 90 degrees or use divining rods, just kidding :-) Something's clearly not right. Could you remove the block from the vice or get it up to room temps?

Are the honing marks visible across the whole of the bore? if not, it's not been bored enough.

Edited by Boosted LS1 on Thursday 7th December 21:20

[PaulKemp]

Could it have been bored with a compression plate bolted on?
Would the block expansion when up to normal running temperature make a difference?
Purely speculation but if so much money had been spent on rods and pistons I wondered if there had been some extra engineering wizardry applied.

[Mignon]

If the bores have 5 to 6 thou ovality as you appear to indicate then clearly it's toast before even getting a chance to run. I couldn't surmise how anyone could generate that big an error though. And no it's nothing to do with deckplates or anything else.

[mtrehy]

There's some honing marks visible but not at a particularly nice angle or uniform. It's a bit of an odd-ball project in that it's a job lot of 3 rare cars, boxes and boxes or spares often with multiples of the same thing - I've got 10 spare cylinder heads etc. The guy was a enthusiast, hoarder, tinkerer. I do wonder whether he did something diy to this block as I found a bit of paper with 1-8 piston micrometer measurements and also a very cheap 3 leg honer in a box of random rubbish - would be surprised if even a total clown could have taken so much out and it be so oval but who knows.

I don't think a torque plate or temps could make that sort of difference - it's 0.005" bigger front to back than side to side and quite uniform across all cylinders on both banks. Only thing I can think is the spindle on the boring bar could have been misaligned or worn and allowing some play in the longitudinal direction.

Anyhow, I've got another block which is now at a machine shop that I know so hopefully can use the good rods, pistons etc on that block.

Cheers

[stevieturbo]

Exactly how are you measuring the bore ?

And what sort of deviation is there from say bottom-middle-top of each ?

How do the pistons actually measure ?

[mtrehy]

Mitutoyo 3-4 and Mercer bore gauge. Pistons measure exactly as per the Ross data sheet that I found in the boxes. There is some variation (within 0.001) top middle bottom but nothing like the consistent difference front to back.

Block is scrap - it's not rare enough to worry about. I was really just interested in how it could be so oval as I've not seen a block that extreme before.

[stevieturbo]

just old, cooked, whatever really.

I had an old 4.6 I bought as a used engine years ago, just wanted a cheap rebuild . It had been a good running engine, so thought it would be simple...no such luck !

Putting it back together, torque the main caps up and the crank wouldnt turn. Bloody block was twisted stupid down the main tunnel. Yet it had been running fine before I got it, and same crank was going back in as it all measured fine.

[Boosted LS1]

Stevie, I've found that the cranks free off once the cross bolts are fitted. Was your's still buggered after that?

[stevieturbo]

Boosted LS1 said:

Stevie, I've found that the cranks free off once the cross bolts are fitted. Was your's still buggered after that?

Yep, the block was screwed for sure.

decided to build it up anyway, despite difficulty in turning the crank...after all it ran before lol. Only to get it started and find it also had a cracked liner. It had probably been cooked stupid at some point.

[Boosted LS1]

Back in the day when I was a youngun I built a 3.5. I could barely turn it over by hand but a breaker bar helped. It ran really well once the starter motor had sorted it out :-)

[Sardonicus]

Boosted LS1 said:

Back in the day when I was a youngun I built a 3.5. I could barely turn it over by hand but a breaker bar helped. It ran really well once the starter motor had sorted it out :-)

Ya cant be youth and ignorance .... thought I had run a bearing on a Pinto when I was seventeen turned out to be a speed braced flywheel only stays secure for 250 miles knew I would be over critical and check it the following day for security/torque pre fitting clutcj assy then back into car guess I forgot