Z1100/1170 head gasket issues

[Steve M]

Good morning engine experts. I am helping a friend with a Z1100 (shaft) that keeps burning holes through its head gasket. It first happened soon after he bought it, between cylinder 3 & 4. The head was then re-faced and reassembled with a new Cometic gasket. After poor running issues were reported again I took the top off again and found it's burnt a hole between cylinder 2 and the cam tunnel. Its probably only done about 500 miles between the two events.

The engine is running high compression 75mm (1170) Wisco pistons. When the correct size head gasket is laid over the upturned head there is a circa 5mm ring of flat head (squish) visible inside the head gasket hole. The gap between the top of piston at TDC and the underside of the squish band is therefore the thickness of a head gasket (1.05mm) plus the gap between top of piston edge and top of barrel (0.2mm) so so a total of 1.25mm which I would have thought would be okay. However, as the head and block now need re-facing it will reduce.

Given that reliability is more of a priority than performance I am considering reassembling with 2 base gaskets to raise the deck height by 0.5mm and therefore reduce compression. Has anyone done anything similar? Does anyone have any better ideas?

I have attached some pictures.

Many thanks.

[warren3200gt]

I had a similar experience moons ago.. Eventually tracked it down to a stud not being put far enough in the crankcase. So although the head nut was torqueing down it was actually torqueing against the last of the stud threads not the head so the gasket wasn't completely compressed.. Oddly enough it was the inner front stud on number two cylinder as it appears yours is. Extra copper washer under the head nut sorted it as it gave enough thread for the nut to compress the washers and gasket and torque against the head.

[Steve M]

Thanks for the suggestion Warren. Just had a measure up and unfortunately that isn't the solution. It would have been nice if it had been!

[warren3200gt]

It's gotta be something like that. Head twisted? Head on a sheet of glass and see if you can get a feeler guage between the two anywhere. I always find a shelf out the fridge is just the right size, when the missus it out.

[zed1015]

You need 1mm piston to head clearance to allow for rod stretch which is why the head gaskets are that thickness.
What compression are the pistons and what torque figure is being used on the head nuts.
The comp ratio of drop in Wiseco piston kits ( and all others) is based on zero deck height and the stock combustion chamber volume which is 40cc on the J type engines.
The 0.2mm on the barrels would be safe to remove to get zero deck height but you need to watch the head volume when skimming the head surface as it doesn't take much to push the comp too far.
Also be wary of skimming the head without first checking that the cams will rotate when bolted in with the head a free state ( unbolted and on the bench) .
If the head is warped you cannot skim the head without it being bolted down on a surface plate to pull it flat first.
If this is not done any warp or twist removed from the head will be transferred to the cam journals when the head is bolted back on the bike which will cause the cams to bind and wipe out the cam shells at the very least.

[Steve M]

Thanks for that, a few things to investigate there. When I put it back together last time I stuck with the standard 29 ft lbs torque as the studs don't appear to be heavy duty.

[zed1015]

Thanks for that, a few things to investigate there. When I put it back together last time I stuck with the standard 29 ft lbs torque as the studs don't appear to be heavy duty.

You can go to 32 ft/lb on stock studs so you should use that and re-torque the next day after first start and allowed to cool overnight.
Then re check around 500 miles.

[Steve M]

Thanks, that's useful to know and could make a big difference.

[Al]

Have you thought about the MLS head gaskets?
AL

[DeadZedDave]

Hi Steve, in your O.P. you wrote:
"Given that reliability is more of a priority than performance I am considering reassembling with 2 base gaskets to raise the deck height by 0.5mm and therefore reduce compression."

This is probably not a bad idea - its been done before !

Looking at pictures its always hard to tell but it looks like maybe several issues here.

That said, as Warren advises, you need the head and deck faces FLAT and then proper gasket prep. and re-torque.

To just get the motor in a usable running condition, proper gasket seal and LOWER compression would be my advice.
An 1170cc motor doesn't need high compression just to get down the road !

Keep in mind that whatever you machine off head or deck face will INCREASE the compression which is not what you want.

Just to mention for reference, back in the day you could buy aluminium alloy or copper base spacers in various thicknesses.
The 1mm squish clearance by the way is a MINIMUM clearance recommended when setting up for racing. You can open that clearance up a fair bit !

[Steve M]

Al, I have not heard of those gaskets but will give it a google. Thanks.

[Steve M]

Dave, thanks for that. I think that maybe the route I will take. He's not a speed freak (like me LOL) but just wants his bike to work!

[Al]

No Ai needed, MLS head gaskets are;
More expensive
Last ten times longer
Dont fall apart like fibre / graphite sh1te
Dont rely solely on pressure to create a seal
Dont need re-torquing
Dont leak even at the oilways
They are shiny
Can in theory be re-used if not damaged
Dont need a formal spearate seal to cam chain tunnel
Are readily available for 1170
Are in use everywhere
Are flame proof and dont have bits that can fall off
Are more forgiving of un-even surfaces
Are made by Cometic

https://suzukiperformancespares.co.uk/p ... ead-gasket

AL

[Steve M]

Thanks Al, I have just ordered one from that very place, along with some bellmouths for my Z1 sprint bike.....

[Skid Mark]

I recently put an MLS gasket on an A2 following Al’s good advise. They are excellent, no issue with leak now and although not sold as reusable, you would be very unfortunate if it cant be used again. Only issue I had was that as I didn’t know the exact modifications to my head, I had to strip and then order, if you are in the UK this will be far less of an issue for you. Also the cosmetic cam cover gasket looks and feels far superior then the ones I used on the thou. ( Versha or Athena I think)