Two head gaskets

[Al.Fisherman]

I built a 80CC bike awhile ago. Then I found this forum and all the good information. I read that the head studs should be changed out because of the **** studs mounted in the engine. Well before I got to order the good studs I had a mishap and blew out the head gasket which isn't any problem. Something puzzles me tho, and that is in all the years that I've been working on engines, the only time we would use two (2) head gaskets is when the head needed to be shaved and two was needed. Well I limped home (I heard the gasket go) and popped the head off to look at the head gasket and check what size the studs were, and to my amazement look what I found...2 head gaskets..My question is, is this common on these engines? Picture below...

 

[Hawaii_Ed]

My slant head 80cc came with two, I immediately took it apart and went to one to raise the compression a bit

 

[Al.Fisherman]

My slant head 80cc came with two, I immediately took it apart and went to one to raise the compression a bit

Mine is a slant also. I'll put just one back, wanted to make sure two wasn't needed. Could you tell any difference between the two and just one. Thanks

 

[Hawaii_Ed]

I am using a shift kit, so starting takes a kick on the pedals, and it was def harder to start, but certainly pulled better with one. Later I went to the sick bike parts gasket which is even thinner. Oh, my top speed is 57 MPH on the flat

 

[GearNut]

Hmmmm...
2 for 1 special?

 

[Dilly Bar Rob]

Same here - both 80cc slant head engines that I have from zoombicycles have 2 head gaskets. I thought it was a factory mistake at first, you never know with these things

I took one of the gaskets out on the first engine and rode it around like that for a couple of days. It did indeed have a bit more power thanks to the raised compression. Not what I would call a night and day difference but you could tell.

In the end I went back to the double gasket setup though - see I only weigh 130lbs so starting the bike can be a bit of an effort for me (rear wheel locks up easy - I have to "slip out" the clutch even with a "stock compression" engine and pedal hard to turn it over, my wife can just dump the clutch and go with no lock up ). I also started thinking about the effect that raised compression might have on the wrist pin bushing... I don't want to tempt the "chinese hand grenade" into exploding...

 

[Al.Fisherman]

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Head gaskets (4..3 extras) came in today from SBP. They are thinner then OEM, and I didn't notice much of an increase in compression (me 210#'s) until my son (135#'s) tried to start it and the rear tire slid on the pavement. I ride mine like I stole it..if this d**n thing wants to blow I want to know. Price is cheap enough to replace.

 

[Hawaii_Ed]

I have never blew a head gasket, but my plug started working loose, I had to tighten it before each ride, and then it blew right out one ride. I heard the first slant heads were a bit weaker, my replacement is fine so far, and still on one SBP gasket.

I hear you on the cost, that is why I keep a spare cylinder head in my bike bag

 

[Al.Fisherman]

Blowing a head gasket wasn't a big thing to me....but oh boy my son...well that was a different story as that is his only transportation. The blown gasket was my fault...I didn't check the torque on the head...a lesson and a cheap one at that...learned. Also all bikes we build and move will have grade 8.8 hardware installed.