Stupid pin height question

[2eighTZ4me]

I will be using 240 9mm rods in a L28 block. This will be a turbo build. I will need to have custom pistons made. Tell me if my math is off.

 

Also - tell me if these measurements are off. I got them out of the "How to Modify" book and I've heard some grumblings that all their measurements aren't exactly correct.

 

My machinist measured the two rods and they were close (within .09") to what the book said.

 

240 rod = 133mm length

280 rod = 130.2mm length

280 pin height = 38.1mm

 

so subtract the difference 133 - 130.2 = 2.8mm

 

Being that the 240 rod is longer - I'd want a shorter pin height.

 

So 38.1 - 2.8 = 35.3.

 

I'd need to get a custom piston - 87mm bore (I'm going .040" oversize bore) with a 35.3mm pin height.

 

Is this correct?

 

I know folks have done this before, but searching through all the "crap" on this site is sometimes like finding a needle in a haystack.

[PalmettoZ]

I will be using 240 9mm rods in a L28 block. This will be a turbo build. I will need to have custom pistons made. Tell me if my math is off.

 

Also - tell me if these measurements are off. I got them out of the "How to Modify" book and I've heard some grumblings that all their measurements aren't exactly correct.

 

My machinist measured the two rods and they were close (within .09") to what the book said.

 

240 rod = 133mm length

280 rod = 130.2mm length

280 pin height = 38.1mm

 

so subtract the difference 133 - 130.2 = 2.8mm

 

Being that the 240 rod is longer - I'd want a shorter pin height.

 

So 38.1 - 2.8 = 35.3.

 

I'd need to get a custom piston - 87mm bore (I'm going .040" oversize bore) with a 35.3mm pin height.

 

Is this correct?

 

I know folks have done this before, but searching through all the "crap" on this site is sometimes like finding a needle in a haystack.

 

 

Hey 280Z4me-

 

I agree with what you say about the search function as well as the search Nazi's that get into telling you about it. Here is a thought-

 

I am building a 3.1 stroker motor right now, and had thought at one time about taking the 280Z piston and taking 3mm off of the top? Since it is a dished piston, I think the first 1.5 or 2 mm or so is just the dish part and you won't be taking off too much of the actual top of the piston. You probably have some 280 pistons around since you have a motor that you are building, get your machinist to measure the piston thickness at the bottom of the dish before and after machining to see how much is actually taken off of the piston. I don't think that the crown will actually be reduced that much.

 

The only problem this might have is the top ring getting too close to the top of the cylinder bore. But this is a money saver for sure.

[ozconnection]

You're math's is correct and you're measurements are spot on.

 

Unfortunately, you shouldn't just go out and machine 120 thou (3 mm's) off the top of your pistons. This is just asking for trouble. Sounds easy enough, however there are probably a dozen reasons why it shouldn't be done.

 

Getting the right piston straight off saves in so many ways, especially the rest of your motor. Even more so if it's a boosted engine you're wanting to build. Pay your machinist to put in the right pistons, not modify the wrong ones.

 

Arizona Z sell pistons exactly for this application, although you might need to talk to them about their suitability for turbo applications.

 

Cheers.

[Xnke]

If a dished piston is ok, get some ITM part number RY-6116-std. 87mm piston, 9.32cc dish, 35.5mm pin height. you'll need a set and a half, as these are for the Z22S four cylinder. I am using this part in 1mm oversize, and have zero deck height.

 

If you need a flat top piston, though, i dunno.

[2eighTZ4me]

Dished is what I'm going for since it will be a turbo build. Problem is - I'm going forged pistons, so I'll be custom ordering them. Thanks for the heads up though!