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Post by flames on Aug 8, 2013 16:27:42 GMT 1
just checked and re checked volumes.i get 13cc in the actual combustion part of the head.(the actual dome part) which is virtually the same as I get on a standard head.with the gasket still stuck to the head,i get 22cc's till the squash hits the gasket ring.allowing for the swell of fluid,i reckon a minimum of 21cc.i was lead to believe this was within tolerance,but will do a compression test to check anyways.also,i get the same measurement for the other side,which shows no sign of blowing.perhaps compression isn't as high this side? I will get there in the end.and when I do,im gunna thrash the effin spuds outa her till she blows,just to show her whose boss!!!
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Post by andypeak on Aug 8, 2013 17:13:02 GMT 1
Another possibility perhaps => with the head skimmed that much and a higher CR could lead to detonation(knock) issues. Knock issues are definitely a gasket killer!
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Post by flames on Aug 8, 2013 17:31:54 GMT 1
this is true.and I have suffered detonation probs before.however,there is no signs of this time.i have ordered a gen yam gasket.will see how that goes.will check compression on it.can someone let me know what the highest figure i should get is?
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Post by flames on Aug 8, 2013 19:59:44 GMT 1
right....something is amiss.probly my measurements,but here goes.squish was 1.08mm,not 1.2mm as I stated earlier.1.2mm was gasket thickness.so here goes
head has been skimmed 0.75mm by my reckoning.which has taken the step out.in theory,this would give a squish of 1.2mm as per the thickness of the gasket. but....ive just measured how far the piston protrudes the barrels,now bear in mind the barrels have been left in situ,and are not tightened down,i get a measurement of 0.7mm.as far as im aware,the barrels are not skimmed.....(if spondon chris reads this maybe he can let me know if he knows).this would maybe explain the 0.75mm step in my standard but ring damaged head.so in theory,1.2mm gasket thickness,-0.7mm piston protrusion,gives me a squish of 0.5mm.which even I know to be too shallow.maybe when I did my squish measurement the piston pushed the solder away from the very edge before it crushed it,giving me a larger reading.
does anybody know how much generally is skimmed from the head normally to enhance compression a little?
the skimmed head I was using came originally fitted to a set of barrels that had the lip skimmed off the top of the barrels aswell.then was running 2 gaskets with a metal spacer between them.im thinking now the spacer and 2nd gasket were used to make up for the skim on the head aswell,and not just the skim on the barrels.
gen yam gasket on order.im now wandering whether to use the other head(with the worst ring damage in one side) or whether to try and get some 1.5mm gasket paper and make my own base gaskets to run with the over skimmed head.decisions decisions.
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Post by yamaha341 on Aug 8, 2013 21:45:07 GMT 1
thats a lot of figures man hope you get it all worked out.. whichever way you go I still dont think you should use that goo / gasket stuff !! head gaskets as a rule of thumb are designed not to be used with any goo especially at the sealing ring the only time I use any kind of gasket compound (and its not goo/or/rtv) is if theres maybe a wee blemish am not happy with and I ALWAYS use YAMAHA BOND 4 the grey stuff and I mean I use it sparingly and defo not on the sealing rings as arrow says the best seal will be metal to metal andypeak also points toward detonation have you checked ignition timing and are both carbs running the same jetting float heights the same silly thoughts but hey you never know something must be different on one cylinder anyway I would shoot for around 140-150 psi ,, my kawasaki500 runs at 135psi and good but my kh250 runs 170 psi quite a difference anyway good luck man I will ask around and if anyone has any more thoughts on your troubles al get to you cheers
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Post by flames on Aug 8, 2013 21:57:21 GMT 1
im going to go with standard head and go from there.it has ring damage,but im sure will be ok.timing set to 1.7mmbtdc to allow for the lower squish.as said earlia,no goo was used on the metal ring.just around the waterways.it was used spareingly,but obviously when torqued down it oozes out.on the plus side,when the gasket was removed,i could remove all residue by simply rubbing my finger over the surfaces.
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Post by steven on Aug 8, 2013 23:05:21 GMT 1
Hi, Standard LC compression pressure should be somewhere in the region of 105 - 124 psi or 7.1 - 8.4 bar. So if you get figures lots higher than 124 psi or 8.4 bar, then you could have too high a compression pressure. My LC with newly rebored oiled bores and rings and 0000.0 miles made 8.0 bar on both cylinders, on a cold engine with 10 kicks with wide open throttle, I will take compression readings once its done a few miles and see how much difference running it in makes to the compression pressure. steven.
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Post by flames on Aug 9, 2013 9:20:08 GMT 1
nice one.cheers for that dude.
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phil38
Thrash Merchant
Posts: 426
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Post by phil38 on Aug 9, 2013 14:05:49 GMT 1
The gasket you have looks like it's made of paper. the genuine yam one i've just fitted is a layered metal one. Putting sealant on the gasket face is bad practice. The surfaces should be meticulously clean (scrpaed off and wiped with brake cleaner). I think putting sealnt on the gasket face and not getting a leak is a case of getting away with it, not the other way around.
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Post by whoisthatdc on Aug 9, 2013 17:43:10 GMT 1
If it wasn't for bad luck, you would have no luck at all albert King born under a bad sign gonna play it at my funeral
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Post by jon on Aug 9, 2013 20:55:49 GMT 1
Gasket sealer is used to take up minor imperfections in sealing surfaces. This is for an unpressurised surface.
A head and cylinder surface is under a huge amount of stress. Both surfaces need to be as square and smooth as possible.
If you think about it Yamaha and the like design their engines to be reliable from new out of the showroom, but it is all new parts.
Are they really interested if people bolt together modified parts off engines that have been apart numerous times on a 40 year old bike?
I think the fact they work most of the time is a testament to the design!
Last time I phoned Nigel at NK racing he told me he no longer did copper gaskets. They are still for sale on eBay from America.
If I were you I'd lower compression to a reliable level, ensure sealing surfaces are as good as possible, and enjoy your reliable LC.
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Post by steve h on Aug 9, 2013 23:28:21 GMT 1
If it wasn't for bad luck, you would have no luck at all albert King born under a bad sign gonna play it at my funeral "Lucy in the sky with diamonds" at mine
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Post by flames on Aug 10, 2013 8:05:25 GMT 1
I have measured the barrels with a digital vernier caliper.they measure the same,however the cases are not the ones I had originally,so cannot vouch for them.i have prepped another head (one that hasn't been skimmed)as I think this is probably the biggest culprit.altho it worked before,as I said it was fitted to a set of barrels that had the top skimmed and ran 2 base gaskets and a spacer,effectively raising port heights and lowering compression compared to mine.hopefully gasket will turn up today,so I will get fitted later and see wot gives.
thanks everyone for your replies and advice
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