I cannot keep the DS650 head sealed with the turbo running 15+psi on alcohol. The compression leaks into the cooling system forcing coolant out of the radiator cap. I have had the head re-surfaced flat. I torqued the four 8mm head bolts to 24ft-lbs. I have torqued the four 10mm stud nuts to as high as 62ft-lbs. I am using a copper head gasket. I have had the cylinder O-ring'd with a stainless 0.040" wire, although it may be sunk too far into the cylinder because when I measure the amount of O-ring above the cylinder it is only 0.005" to 0.006". The head has a shallow receiver groove above the O-ring. The motor doesn't have a good design in terms of head bolts. There are only 4 head bolts, with 4 studs. I was told 5-6 head bolts are needed for good head sealing.

See F650 pictures:

cylinder picture

head picture

Is the stainless O-ring sunk too deep? Would adding a second ring help or would this not gain anything? Would a larger diameter O-ring be better? The shops I've called say 0.040" is standard and no-one yet would go any bigger. Would a gasket other than copper be better? Does anyone know of a shop that installs larger O-rings than 0.040"?
Would non-metal O-rings work better such as used on 2-strokes? Is there some other kind of custom groving that can be done to create a lock between the cylinder and head?

I was told to be sure I am not running too much timing which could cause unnecesarily large cylinder pressure. I lowered the static compression ratio to around 8.3:1

Thanks.

 

Maybe I'm missing something here, but I don't see any groove for the O-ring to fit into??

My cylinder is also O-ringed, and you can CLEARLY see the groove for it in the top of the cylinder. Am I missing something here??

 

Yeah...the oring seems kinda faint....???

What thickness copper gasket are you using? Depending on the thickness- I think that you could go about .010 high on the wire.

Looking at your cylinder, I can see 4 places that it would be "easy" to add a 8mm stud. Getting them in the head may be more diffcult.

Ultimately though, I do think that the addition of more studs will be the solution.

 

The TAD engines I used to work with were o-ringed on the block, used a solid copper gasket, and no reciever groove in the head. Half the o-ring diameter was above the suface of the block, this bit solidly into the gasket.

Denny

 

Is the gasket leaking on the head side or the cylinder side? I am not familiar with o-ringing atv engines, but in the automotive world, heads can also be o-ringed. Usually this is only done with extreme amounts of nitrous or boost. The o-ring for the head is machined with a wider diameter than the blocks o-ring. This gives two positive sealing surfaces.