New block worries

[DangerousDerek]

Put the crank and pistons in the new block. Offside looks ok and i am seeing about 7 thou deck height on all 4 pistons. But looking on the nearside they are not square. The fronts of each piston sits flush with the deck and the rears of each are 8 thou under. How can this be?

[QBee]

Do you get the same result if you rotate each piston 180 degrees? (assuming you can do that)

[DangerousDerek]

QBee said:

Do you get the same result if you rotate each piston 180 degrees? (assuming you can do that)

I suppose i could as an experiment. But i would have to take the pistons off the rods and getting those spring clips out is something i dont want to attempt if i dont have to.

[carsy]

Derek its quite normal that the pistons are not completely square with the top of the block. I put it down to the pistons having offset pins which i assume yours have.

[DangerousDerek]

carsy said:

Derek its quite normal that the pistons are not completely square with the top of the block. I put it down to the pistons having offset pins which i assume yours have.

1 bank all 7 thou down and the other bank flush at the fronts? Seems very wrong to me.
Not only something amis geometry wise but means i would have higher CR on 1 side of the engine.

[DangerousDerek]

I just swapped piston 4 into pot 3 and its the same.
So i guess the rods are fine and it must be down to the new block.

Back to ACR with it tomorrow!

[Bassfiend229hp]

So does that mean the bores on that side aren't perpendicular to the crank???

[QBee]

DangerousDerek said:

I just swapped piston 4 into pot 3 and its the same.
So i guess the rods are fine and it must be down to the new block.

Back to ACR with it tomorrow!

That was the point I was making by suggesting you spin the pistons around - it sounded to me like the block wasn't machined quite level on one bank
Presumably you will be taking it back assembled so they can see the problem?

[spend]

Have you put the rods on the right way around?

Along the crank the pistons should be equal... Across they will be different, as the geometry is about rotation rather than symmetry (on the C/L), and based on the offset of the pin in the piston.

[DangerousDerek]

All the chevy rods are chamfered so its obvious which way they go.

[DangerousDerek]

I swapped 2 and 3 over just as an experiment and they were the same.
Swapped them back now.

I have found that a good bit of thumb pressure on the front of the cock eyed pistons can get them flat to the deck but it cant be right they sit the way they do while 'resting'

[davelittlewood]

Derek,

When you say 'front' you meant the front of the car? (not the outer of the V or the Inner of the V?)

If that's the case then it must be the pistons otherwise the block top has been machined on the piss and you wouldn't be able to have the same drops on each piston as the drop would be much high on the front piston compared to the rear (or the other way round).

[Bassfiend229hp]

davelittlewood said:

Derek,

When you say 'front' you meant the front of the car? (not the outer of the V or the Inner of the V?)

If that's the case then it must be the pistons otherwise the block top has been machined on the piss and you wouldn't be able to have the same drops on each piston as the drop would be much high on the front piston compared to the rear (or the other way round).

But what if the bores weren't machined absolutely perpendicular to the crank?

Phil

[davelittlewood]

Bassfiend229hp said:

But what if the bores weren't machined absolutely perpendicular to the crank?

Phil

Eh, yes, hadn't thought of that one!!

[Pupp]

If you're using forged pistons, you'll probably find they are considerably wider across the skirts front to aft that the dia of the crown; this is due to the quite different expansion characteristics of the material compared to cast units which, although they will vary in the same comparison, will be much less pronounced (it's also why forged slugs might slap until warm).

If they square up by pushing on them or by rotating the crank backwards, sounds exactly as I'd expect (the piston will naturally try to tip as the crank rotates due to ring friction etc).

[Sardonicus]

Derek it's like this if one bank is one thing and another bank is another then there are machining woes, sorry to be blunt but I think you know already Know this ??

Edited by Sardonicus on Sunday 23 August 19:06

[DangerousDerek]

Having had a nice chat with a respected engine builder it seems I may not have a problem after all. There are a couple of checks I still need to do but it looks like the build is back on.

[Pupp]

Do tell us more...

Glad it's good news

[Sardonicus]

DangerousDerek said:

Having had a nice chat with a respected engine builder it seems I may not have a problem after all. There are a couple of checks I still need to do but it looks like the build is back on.

Please spill the beans Derek I'm confused here are your quoted measurements correct or was this an assembly error?

[QBee]

After all the engine build threads on PH TVR in the last couple of years, it is nice to see the words "respected" and "engine builder" in the same sentence again.