Superjet blowing out ADA o rings

[john zigler]

We use many ADA heads here as well. I use Newton Meters for torque. I torque head bolts to 30nm, and girdle bolts to 40nm.

I do it is 4 steps. 10, 20, 30 , then final 40 on the girdle bolts.

Has always worked for me.....

 

[bored&stroked]

Love my stock heads machined for whatever compression I want and using 760 gaskets....don't have to worry about blowing out orings.

 

[Quinc]

Love my stock heads machined for whatever compression I want and using 760 gaskets....don't have to worry about blowing out orings.

Head gaskets are freaking expensive though.

 

[JetManiac]

Love my stock heads machined for whatever compression I want and using 760 gaskets....don't have to worry about blowing out orings.

Ultimate reliability, but ....don't have to worry about making as much power either, with stock domes shape and big squish band with even 760 head gaskets.

 

[bored&stroked]

Ultimate reliability, but ....don't have to worry about making as much power either, with stock domes shape and big squish band with even 760 head gaskets.

Yeah but if your machining a new dome for whatever compression you want, can't you machine the dome to whatever shape you want as well?

 

[Storbeck]

Yeah but if your machining a new dome for whatever compression you want, can't you machine the dome to whatever shape you want as well?

The distance from top of piston to top of cylinder, plus thickness of head gasket, you can't machine a dome to have squish band smaller than that. If that is more than the squish band thickness you want, you have to eliminate the gasket or use a thinner one.

 

[JetManiac]

Yeah but if your machining a new dome for whatever compression you want, can't you machine the dome to whatever shape you want as well?

Head gasket is too thick already like Storbeck said above. And can't reshape domes easily if too big in spots already. And no ability to girdle the cylinder to protect it.

 

[kevbo]

Its unlikely any manufacturer will improve anything that was designed for an out of production vehicle. The problem can largely be fixed by lapping the deck and possibly shimming domes. Sometimes a new complete head is necessary.

 

[Vortex]

Also make sure the acorn nuts are not bottoming out on the studs.

 

[bored&stroked]

And no ability to girdle the cylinder to protect it.

My protec girdle and groupK have proven otherwise haha.
I get the squish band. The domes being too big thing still mystifies me. For instance, I had a 701 head machined for the 84mm bore in my 61x cylinder. It seems weird to me that the domes could be too big in a 701 head for that application to be made optimal as far as dome shape [which is different then squish clearance]. But, I've never played with heads on a 2 stroke before either so theres that.

 

[whennotsailing]

Finally getting back to this and would appreciate your help. Maybe a few of these pics will explain more? I cannot see/feel any drop in the cylinders... It might look like it in a photo or two, but if anything they are raised ever so slightly. I can feel it when I run a dental pick across the two surfaces. The sleeve separates where I colored red, correct? They are just pressed in?

If you look close (circled in blue on one of the photos), there is some detonation on the front side of the rear cylinder. I can also take either dome and rock it every so slightly on the rear cylinder top.

Last, you can see the rubber o-ring from dome to head had a bit of a meltdown. I think the cut you see happened when I hap-hazardly tapped on the plug to get the dome out for tonight's photo op. I do recall that when I tried to remove spark plug beachside (post failure), the dome was turning under the head, but that was maybe due to oring already being toast.

So, based on the photos, what's next? Can I get top of jug machined flat ? Is head an issue? Domes?

 

[Harbor]

Yes the sleeves press in and that gap you feel with pic is one of the edges of sleeve to the cast cylinder bore.... the small dome oring wear must be from the dome spinning like you mentioned, no flame front up there, it does look melted from heat ? Or may be an illusion or dirt

Yeah the deck needs re-surfacing, they can inspect the cylinder pitting and make any recommendations there...

If you don’t see any wear on the tops of the domes where they contact the inside of the head shell and you see no wear to the corresponding head shell contact points to domes, then head is probably ok...

If you reuse the head and deck the cylinder watch for dome spin when tightening your spark plug @ assembly.. if it spins get a new head shell abs domes...

 

[mikidymac]

Circled in blue on the cylinder isn’t detonation, it’s pitted from rust.
If you can feel the domes rocking then the top of your cylinders aren’t flat.
Get the cylinder decked at have the shop check the domes for flatness.

 

[JetManiac]

Also post a few pics of your head shell top and bottom

 

[whennotsailing]

Some pics attached.

In response to some comments, no rust present on front of rear cylinder. That's just two strokey goo and blow by I think from dome not making contact.

 

[Blue]

Is it a bad pic or is the head shell worn in this picture where the dome sits? Near the oring. Looks worn to me.

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[Big Kahuna]

There should not be any black sludge, soot in the underside of the head body light that, you got orings that were leaking.

 

[whennotsailing]

The o ring is melted, but I think because dome is loose under head. Head appears to be in fine shape. Look at this pic. There's a slice in the oring too, but I think that is because I carelessly tapped head and plug against toolbench to pop the dome out for pics.

 

[whennotsailing]

Sounds like a trip to machine shop with head, domes, jug is in order. Agree?

 

[Blue]

Yes for sure.

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