pistons hitting headgasket

[Guest]

Hi, I'm working on my 83 750e 3rd gen motor today. I pulled the head off to put in heilcoils in all my cam caps (all 24 of them) I also am replacing a wrist pin that I KNOW to be worn (will also be replacing the two top rings of each piston, not the oil ring). After I removed one of the pistons I was looking at it and I noticed that there is a impression of my headgasket on the crown of the piston as if the piston was coming up and smacking it. It's not just a discoloration, if you run your fingernail you can feel it, heck, you can see it. is this normal??? Thanks for your help

[05Astro]

I would think no, is it the cylinder with the worn wrist pin? Ive never seen a head gasket hang into the cylinder on a stock machine. Is the bore size standard?

[helmutholderbenz]

No, its not stock. I put a 816cc kit in and I milled the head and decked the block over the summer. When you use the wiseco kit you still use a stock headgasket

[05Astro]

I was on APE s web page and they make mention of using a modified stock head gasket. Maybe give them a call? Jerry

[Chuck78]

Yeah, you don't want the gasket ever hanging into the cylinder like that. This means the gasket is compromised because it has only about 3/16" compression surface around the cylinder to seal on a composite gasket, & now you'd have less. Also you need the thickness of the gasket to help keep the piston from smacking into whatever is above it, usually just the head only, not a gasket in the way!

ALWAYS go big bore gasket if the stock or aftermarket standard offering gasket is not bigger than the bore of the cylinder

[helmutholderbenz]

I don't think they make a big bore gasket for this motor 750 3rd gen. oem is a 3 ply metal gasket and thats what I'm using. I have the jug here on the bench and I can see that the headgasket does stick over into the bore some, I also see that my pistons were hitting the gasket a little bit, not much cos the top of the gasket is still smooth and flat and undesturbed. Like I said, I decked the jug over the summer, maybe I took a little too much off! On the other hand, I made sure the pistons weren't sticking out of the jug when I put it together, actually I thought I could have taken off a little more!

[Chuck78]

Here ya go, straight from the GSZone.biz (APE Racing) website:
"Cylinder boring only. '83 GS750ED and 750 ESD must use modified OEM head gasket."
I don't believe you read that before you installed your OEM multi-layer steel gasket...
I find it hard to believe that they don't make a big bore gasket to go with this big bore kit.
I probably would not recommend taking any sort of sanding or grinding tools to the MLS type head gasket, as you definitely do not want to get any abrasive material or metal particles in between the layers of the gasket. I would think that cutting it would be a much more appropriate technique, but you should consult Big Jay at APE Race Parts, who is a regular contributing member on this forum, as to how you are supposed to modify them. It is important to have the proper quench distance or squish band, and you basically have eliminated that at the edge of the piston by having the head gasket in the way. Bad idea.

John Baker at gasketstogo.com can make you a one-off gasket for $120 in many different thicknesses of MLS Spring Steel, or can make 5+ of them for around $80 or $90 each. John does great work.

[helmutholderbenz]

Thats funny, The wiseco site just says to use a oem gasket, doesn't say anything about modifying it, yet the ape site says to use a modified oem gasket. I didn't notice this problem till after I decked the jug. I think that using just the oem gasket would have been fine untill I decided to try and achieve 0 deck height. On the bright side, I think I found where my little knocking sound was coming from

[Big Jay]

Wisecos catalog says must use modified oem gasket That's where we got it from. However, they also list a big bore gasket, but it is the fiber type with compression ring, not the multi layer steel.

[blowerbike]

is all 4 pistons hitting?
just saying if it's only one piston making contact the rod bearing may have turned.

[helmutholderbenz]

Wisecos catalog says must use modified oem gasket That's where we got it from. However, they also list a big bore gasket, but it is the fiber type with compression ring, not the multi layer steel.

My motor is a 1983 GS750e 3rd gen. are you sure wiseco makes a big bore gasket for this motor because all I saw was must use oem gasket. For the 2nd gen they do make a big bore gasket, the fiber one like your talking about. Please correct me if I'm wrong.

[helmutholderbenz]

is all 4 pistons hitting?
just saying if it's only one piston making contact the rod bearing may have turned.

Yeah, all 4 pistons touch but its ever so slightly. I'm pretty sure I will have enough clearance if I can get the head gasket right

[Big Jay]

My motor is a 1983 GS750e 3rd gen. are you sure wiseco makes a big bore gasket for this motor because all I saw was must use oem gasket. For the 2nd gen they do make a big bore gasket, the fiber one like your talking about. Please correct me if I'm wrong.

The catalog shows GS750 1980-84 Gasket #W4937

[helmutholderbenz]

The catalog shows GS750 1980-84 Gasket #W4937

Yes, but the catalog also makes note that the 83 ED/ESD must use a modified oem head gasket. I don't think #4937 is a modified gasket

[helmutholderbenz]

I was thinking about my head gasket problem today and came up with the idea to machine a little relief in the crown of my pistons. That way in the future I can just use a regular gasket. Is there any reason I shouldn't do this?