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Cylinder head scrap ?


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Ok question for today folks!

 

Back in the day when I owned BUO for the second time I fitted a triumph tune stage 3 head, being young(er) then and having more money than sense I quickly took the head off and sent it to Oselli engineering when they where still based around the corner from Cammeron in Witney. They did the 'full works' on the head including fitting even bigger vales with thin valve stems and 3 angle valve seats. It was a thing of beauty and I was kind of sad to have to bolt it back on the engine but I remember at the time the remaining 'land' between the inlet and exhaust was very VERY thin. At the time the compression was 215 on each cylinder ( you could still get good old 4 star so it was running 10.75:1 if I remember) Anyway just done a new compression test (using the same compression gauge!) and we now have 1,3,5 and 6 at around 190 but no's 2 and 4 are 175 so I suspect that 20 years of running on unleaded all be it with additive have taken their toll.

 

She's not smoking, but she has done about 70'000 miles on the engine so I'm assuming that the overall compression loss is down to a bit of wear it 2 and 4 I'm more concerned about, I could whip the head off but just conscious of the engines age and 'opening a can of worms' but sooner or latter will need an engine rebuild (probably sooner) and trying to get a feel for if I need to start looking for a new head or if opinion would suggest mine is salvageable given the amount of previous surgery its had.

 

All the Best Graham

 

 

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Graham,

Running high compression on less than optimum octane fuel would not damage the valves first. Its the ring lands on the pistons that knock will affect the worst. So the low compr test readings might reflect a bit of piston damage. Do the readings improve with oil in the bore?

 

And valve seat recession - assuming the Oselli mods did not include hardened seat inserts - needs sustained high load driving at over 3000rpm. So in normal road driving I think I it would be difficult to destroy valve seats in 70k miles. And If you used a manganese based octane booster that will do the job of lead.

 

I've never done one but a 'leak down' test might tell you what you need to know without taking the head off. Maybe the seats are little tired. But I doubt the head is scrap.

 

Peter

 

Interesting that 2 and 4 are consecutive in the firing sequence...

Edited by Peter Cobbold
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