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Cp Piston To Bore Clearance And Ring Gapping

TriniGT

By TriniGT,
in Engines & Forced Induction

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proengines Rising Star

proengines

Posted
Posted
appreciate the response mate. did you manage to get those pics of the rd28? or too busy? no issue if not.

Have you ever checked bore with and without torque plate to see what variation there is?

No problem. I'll get to the RD28 tomorrow I hope, have spent the last few days porting so I'll be glad to be doing something clean for a change. There is a definite difference in shape with the torque plate on, I bore them without it and fit it to hone the last .005-.006" out. You can feel the hone chatter when you start, there are high and low spots at the top inch or a bit more of the bore. You can see pretty plainly when you pull one apart that isn't torque plated, there are always shadowy bits in line with the head bolt threads where the rings don't seal properly.

Cheers,

Greg

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BoostdR Mentor

BoostdR

Posted
Posted

The Jap spec piston to bore clearnace are not as good as you may think. If you can read Japanese you will find this spec is when the piston is heated to a nominal Temp, Many a non suspecting builder have overlooked this fact an picked up the bore.

Nothing wrong with CP

  • 1 year later...
marksuxass Collaborator

marksuxass

Posted
Posted
Completely agree with this!

I ended up giving my CP's the flick in favour of a new set of Tomei's and never looked back

thinking of running tomei's in mine, would you highly recommend?

also please share your piston to bore, and ring gap specs if you dont mind? :ermm:

  • 8 years later...
Tangles01 Enthusiast

Tangles01

Posted
Posted
On 7/14/2009 at 9:55 AM, r33_racer said:

Sorry for hijacking the thread, but I have a question....

Since most blocks when bored/honed are done with a torque plate(well if done properly)...if you were being precise with your ring gaps, then it would make sense to check and set ring gaps whilst a torque plate is bolted to the block right?

Does anyone do that? or only pedantic builders goto that length? I understand the bore distortion might only be .0005 or thereabouts going from torqued to untorqued.....but still...might only be half a thou, to some thats not much, to others thats alot.

Been thinking about it, and was curious if anyone bothers?

Man I've been searching for hours looking for a direct answer to this. I know they "should" be gapped using a torque plate, but well I don't have one and when people are talking about gaping them, they never seem to mention if they were using one, I find it hard to believe everyone has a mate with a torque plate. I'm on hold on mine just trying to confirm I though I had found some good evidence to just open them up another 2 thou to allow for the change when the head is bolted. But can't seem to find it. Anyone else got some input on this? I'm inclined to think that I'll be fine with the slightly bigger gap as state, or is even that not worth bothering with?

GTRNUR Grand Master

GTRNUR

Posted
Posted

No, you don’t need to torque plat the block when gapping rings.

The way I do it, which is probably a little over cautious, is to measure the height of the first and second ring lands on the piston with a vernier.

Then measure your ring gap with the ring positioned in the block at that height.

You will notice that the ring is in the area of the block which is still the upper deck. This area will not distort with a torque plate installed and studs are tensioned.

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