TOPIC:

The FCR35s set I have was made specifically for a nearly stock KZ1000-J with opened up intake and exhaust. I believe you go bigger ID with Flat Slides.

I still think the pump gas here is borderline at best. That graph might be pretty accurate for being optimal on old-school cast iron block and heads, and down a couple of points for an Aluminum KZ.

I think you're right on going zero deck height. First thing I'll check.

Hey...wait a minute? The outer edge of these pistons are not flat, but have an inward slope before the dome. And the head deck extends bout a 1/4" into the bore. So zero deck height may be too tight a squish. See what I mean?

That cannot be correct.
Stock J head has a 69.2mm combustion chamber dia at the gasket face which would leave approx 1.5mm exposed when boring to 72mm.
Nowhere near enough to be of any significance. (stock bore 69.4mm )
To get around 1/4 inch (6mm ish) you would have to be over bored to 82mm at around 1400 cc and on a big block.

I'll measure when I get home later. I got another head and you can see the carbon on the deck within the head gasket ring marks. May show a little more because I used the OEM 1100 gaskets.

The 1100 is 1089cc at 72.5 bore and using that gasket would leave an approx 2mm void between the head and liner top where oil and carbon will accumulate.
Additionally the carbon build up would not stop there but creep over onto the combustion chamber as usual.
It is this that is visually giving you the wrong impression that the head face is protruding into the bore when it is not.
I have 2 uncut J heads on the bench right now on similar engine builds and they both measure 69.2mm.

Sounds like you know better than I. I'll check the deck height and see where I'm at.

You were right about the 1/4" exposed. I looked at it real quick running out the door this morning, and the carbon at the flat deck and combustion chamber slope blended in.

I measured from the gasket ring imprint and the combustion chamber and got about 2.5mm.

I then measured the ID of a Cometic and OEM 1100 gasket and got 72.12mm and 73.42mm respectively. Do you see that extra 1.3mm causing any problems?

I also measured the Cometic and OEM thickness and got .046" and .053". You said Cometic is .043", and I assume that's post-torque. If so, I guess a good estimate on OEM would be about .050". Meaning zero deck height still wouldn't reach .040" with OEM gaskets. But seeing combustion chamber width at 69.2mm on a 72mm bore, I should be looking at deck height about 2.8mm in on the piston to account for the piston slope.

Thanks man. You know your stuff and I really appreciate your help.

are you sure you have the correct pistons ? the MTC catalog only lists a 1075 kit for a KZ ( 2mm over stock ) not for a J motor.

VTEC wrote: I then measured the ID of a Cometic and OEM 1100 gasket and got 72.12mm and 73.42mm respectively. Do you see that extra 1.3mm causing any problems?
.

That equates to the gasket sitting back only 0.65 mm which will then be reduced slightly when compressed..
It will cause no issues.

As for the pistons. Are these new ?
All the newer ( for many years now ) MTC and Wiseco pistons are forged and the band around the dome is machined flat to correspond with the head.
Earlier pistons of both manufacturers were cast and may have a slight slope but I have no examples of these to compare.
All my MTC and Wiseco are forged and have a machined flat band .

gpz1170 wrote: are you sure you have the correct pistons ? the MTC catalog only lists a 1075 kit for a KZ ( 2mm over stock ) not for a J motor.

No. They do make a J kit also. 10.5:1 part #MTC-J1075

zed1015 wrote:

VTEC wrote: I then measured the ID of a Cometic and OEM 1100 gasket and got 72.12mm and 73.42mm respectively. Do you see that extra 1.3mm causing any problems?
.

That equates to the gasket sitting back only 0.65 mm which will then be reduced slightly when compressed..
It will cause no issues.

As for the pistons. Are these new ?
All the newer ( for many years now ) MTC and Wiseco pistons are forged and the band around the dome is machined flat to correspond with the head.
Earlier pistons of both manufacturers were cast and may have a slight slope but I have no examples of these to compare.
All my MTC and Wiseco are forged and have a machined flat band .

You may have caught me in a quick look scenario again. I'll look at the band again later.

Just thought that if I take a significant amount off the block deck I'd also have to deepen the o-ring grooves to use the OEM gaskets. Otherwise they may be too tight.

Right again Zed. Pistons are straight on the edges. You know theses engines well.

So it's looking like using the 1100 gaskets is becoming more and more problematic. What's your experience with the Cometic.

This engine cannot Leak. I'm rebuilding after someone else rebuilt it and everything was a disaster. Including the Cometic gaskets leaking oil at all 4 corners. Of course I discovered that both decks weren't flat, but I've read lots of stories about them leaking regardless.