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Post by hardhatharry on Oct 27, 2016 19:44:26 GMT 1
Holy thread resurrection Decided to get the head skimmed and the guy said he hadnt seen one that bad for a while, some hopefully fingers crossed we have a fix  |
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Post by 1966baz on Oct 27, 2016 20:04:37 GMT 1
Snap, my Mars bar 31k engine hybrid has just blown its heads gasket after a very spirited ride. It goes like stink running 2.00 mm oversize pistons. Just when I thought it was running great. I will investigate further at the weekend.
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Post by stusco on Oct 27, 2016 20:16:58 GMT 1
My 31k head was fine but the barrel tops needed skimmed you ould see a track across the liner causing gasket failure
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Post by Tobyjugs on Oct 27, 2016 22:36:04 GMT 1
I used a pattern gasket as the holes were bigger than the original Yamaha gasket. I think it was an athena gasket. I got it from Norbo.
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Post by hardhatharry on Oct 27, 2016 22:58:35 GMT 1
I have a gen yam gasket that has been bored out to the correct size to go on
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Post by jackjabba on Oct 28, 2016 8:58:34 GMT 1
Probably best to get it O-ringed and save on future gasket failures.
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Post by hardhatharry on Oct 28, 2016 17:13:45 GMT 1
|If it needs o rings I will get a coolhead instead
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Post by 4l04ever on Oct 28, 2016 17:47:52 GMT 1
I had a jig made from 25mm steel to hold a pair of barrels while they are skimmed as a pair to make sure they are perfectly flat and in line with each other. If anyone needs any done, get in touch.
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Post by jon on Oct 28, 2016 18:50:46 GMT 1
One thing to mention about a possible cause to increase the likelihood of gasket failure is compression.
By the look of ŷour head the domes are standard so the extra compression would increase the likelihood of gasket damage.
Unfortunately this will have been made even worse with the skimming.
If it fails again I'd be very tempted to increase the dome volume while it's off.
Jon
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Post by hardhatharry on Oct 28, 2016 19:15:24 GMT 1
Had a chat with Mick Abbey about possible compression issues but after a long chat about the setup he said it should be ok even after the skim
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Post by bare on Oct 28, 2016 20:30:49 GMT 1
From the looks of your Photo (that is your head after skimming?)
It is ...Nowhere near... being a compression issue.
There's still a lip to the squish band and the half round casting at the head's front hasn't been touched/surfaced.
That said: last possible oversize Slugs may be different ?
If still in doubt use a Calibrated liquid measure in the comb chamber.. and find out
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Post by hardhatharry on Oct 28, 2016 22:44:26 GMT 1
yes head after skimming
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Post by steven on Oct 29, 2016 2:06:50 GMT 1
....to rule out the too much compression question, dont settle for "it should or it might be ok"......do a compression test, but I understand that might be a little difficult if its now in bits, but will give you the definative answer once its all back together.
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Post by jon on Oct 29, 2016 8:47:48 GMT 1
The point I was trying to make is if the bore is on 2.25 with standard domes, then already the compression maybe too high.
This is before skimming.
I'd check if I were you and not just the volume, but the compression ratio.
Jon
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