Stripped my B this morning

[scouse]

Some of you know that my B nipped up on the way the north West Rally.
I'm not convinced that a blowing head gasket was enough to cause this?

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[Nigel S]

Lesson to us all Gary. Don't leave that leaking head gasket for too long, or this could be the end result.
Will you get away with a hone and a new piston ?

[scouse]

Nigel I think so, but I'm not convinced that was the issue, will have proper look next week

[Mitsui Spy]

When the head gasket failed on my 400 it instantly demolished the piston.

[scouse]

So maybe that is the issue then

[Treeman]

I have been running my scruffy S2A with a leaking head gasket for a while - I did not realise the significance Better get that sorted

[Mitsui Spy]

Well, I'm can't say categorically it was the head gasket but that's the only conclusion I could draw. It had nipped up previously but the inlet stubs were very worn and the carbs were pretty loose. I renovated the inlets and gave the bore a bit of a hone. Rebuilt it with new gaskets, took it for a short run the next day then retorqued the head bolts. Did 50 miles at 60 -70 on the motorway then suddenly out of the blue ..."BLOOOOOR!" . Coasted to the hard shoulder, let her cool down, tried to start her but sounded very sick. Limped a mile or two to the nearest exit and pulled the top end off. The head bolts were not much more than finger tight! The front edge of the piston was totally melted through.

What I think happened was, the base gasket relaxed over the first 50 miles until the head gasket lost its seal. Big in-rush of air instantly melted the piston. Never heard it coming. I believe my short run in the morning (a couple of miles to the petrol station) didn't provide enough heat to settle the gaskets so I had re-torqued them before they'd fully relaxed. With seizures there's always a tad of doubt floating around but that's my theory for what happened to me.

I've run bikes with weeping head gaskets before and it's not been an issue, clearly it depends on the type of leak. A bit of oily residue getting forced out under very high combustion pressure is most likely fine, but when a head gasket is so far gone it lets air be drawn in under relatively low pressure it's a very different matter. Was your head still fully tight Gary?

[scouse]

Well, I'm can't say categorically it was the head gasket but that's the only conclusion I could draw. It had nipped up previously but the inlet stubs were very worn and the carbs were pretty loose. I renovated the inlets and gave the bore a bit of a hone. Rebuilt it with new gaskets, took it for a short run the next day then retorqued the head bolts. Did 50 miles at 60 -70 on the motorway then suddenly out of the blue ..."BLOOOOOR!" . Coasted to the hard shoulder, let her cool down, tried to start her but sounded very sick. Limped a mile or two to the nearest exit and pulled the top end off. The head bolts were not much more than finger tight! The front edge of the piston was totally melted through.

What I think happened was, the base gasket relaxed over the first 50 miles until the head gasket lost its seal. Big in-rush of air instantly melted the piston. Never heard it coming. I believe my short run in the morning (a couple of miles to the petrol station) didn't provide enough heat to settle the gaskets so I had re-torqued them before they'd fully relaxed. With seizures there's always a tad of doubt floating around but that's my theory for what happened to me.

I've run bikes with weeping head gaskets before and it's not been an issue, clearly it depends on the type of leak. A bit of oily residue getting forced out under very high combustion pressure is most likely fine, but when a head gasket is so far gone it lets air be drawn in under relatively low pressure it's a very different matter. Was your head still fully tight Gary?

Hmm I'm not sure, I remember undoing the left hand head and thinking "that's not very tight", I should have paid more attention when I attacked the heads with my battery ratchet

[SAM]

Sorted my S2 cylinder head yesterday. Nice to have a clean engine as well.

[doodah]

I'd suggest that you should check the cylinder head isn't warped.