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Head gasket question

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

Guest
I've had the cylinders re-bored for 1mm oversized pistons (i.e 69mm to 70mm).
The OEM head gasket now sits slightly proud of the bore (about 0.5-1mm) as it is smaller diameter than the bore.
The pistons at TDC are just 1mm (or less) below the cilynders block's surface and this is without torqueing the head retaining nuts.

I'm worried that when I torque the head down and the engine heats up possibly the gasket's metal rings might interfere with the pistons. :eek:

I thought I'd better ask for your opinion here on the forum than be sorry later ...

Thanks for any thoughts
 
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I've always had to buy larger bore head gaskets with larger pitons. Not sure about 1mm over though.
Maybe take it in 1mm with a dremmel?
 
You need to order the CORRECT 1mm overbore gasket. Cometic will be your best bet. Do NOT grind the ring on the stock gasket! I'll bet the 70mm gasket for the 8 valve 750 will work! 1mm bigger is ok, 1mm smaller is NOT! Ray.
 
suzuki doesn't seem to list oversize gaskets for 850 so not sure what their thinking was?

ray, are you sure the 8v 750 is 70mm bore? cos 850 stock is 69mm.

would maybe a gs1000 gasket be suitable if anyone knows?
i'm pretty sure it would fit but not sure of the bore size.
 
Stock 750 is 65mm but I've seen 69mm for over bored 750's. A 70mm 750 would obviously fit your 850 too. Surprised they make them for the 8 valve 750 though cause there wouldn't be much of a cylinder left.
 
I was thinking of the 70mm gasket for the 3mm overbore on the 16 valve 750. My bad! Dar is right on the 1000 gasket in your case. Ray.
 
cheers guys it's all starting to make sense now :o

i bet what the z1 sells is a 70mm stock gs1000 gasket that also works fine on the 69mm stock gs850 and would be perfect for my 70mm overbore

i'm waiting the response from z1 just to be sure but will likely get the gasket from them

thanks again gsr :)
 
Well just measured my head gasket from 850 gasket set and its ID is 73mm for 69mm cylinder. So then measured head gasket from 750 gasket set that I installed last year and its 67mm for 65mm cylinder.

So there out there.
 
Coady said:
Well just measured my head gasket from 850 gasket set and its ID is 73mm for 69mm cylinder.
Click to expand...

what brand is that set coady? i wouldn't be surprised if they're covering 850/1000/1100 models with one and the same gasket so save costs...
 
NP gaskets with an apple shape logo. I bought the set from UK on ebay. They have all the oem part numbers on the back for GS850 gaskets, but I guess The head gasket could shared between a few sets as you've suggested.
 
Been thinking... put my head gasket on last night and it did look a little large for the bore with the 2mm gap around the edge - 73mm for 69mm bore...

Put it back together and was gonna put the valve cover on when I thought I should sleep on it (probably should have stopped a little sooner..).

Worried now I may lose some compression? Am I worrying for nothing?
 
Coady said:
Been thinking... put my head gasket on last night and it did look a little large for the bore with the 2mm gap around the edge - 73mm for 69mm bore...

Put it back together and was gonna put the valve cover on when I thought I should sleep on it (probably should have stopped a little sooner..).

Worried now I may lose some compression? Am I worrying for nothing?
Click to expand...

Well I've calculated that this will add about 1.8cc overall, assuming that the stock gasket is exactly 69mm wide and that the head gasket is 1mm thick (it was before it's torqued down). This would change compression ratio from assumed stock of 8.7:1 to 8.55:1.

I'm thinking this is negligible....
 
size

size

i had to buy a new one for my 1166 kit. stock was way to small lol
 
Shawn, the stock 1150 head gasket works REALLY well if you just open it up a little for an 1166! Ray.
 
I sold a guy an 1150 gasket that Ray cut and it worked a charm.
Not to say I had my doubts.
 
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