low compression/burnt valves. - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 26 (permalink) Old 10-07-2013, 06:21 PM Thread Starter
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low compression/burnt valves.

I have an 86 mod vn showing 60000kms,fitted with stainless drag pipes on the original collector. The compression figures are 75 psi even, on both cylinders.
My question is, at a guess do you think I have worn rings or burnt Valves?
Relative to the fact I'm demonstrating half of the minimum compression allowed.
I took the compression stone cold with the throttle open, though my manual suggests the reading be taken hot. I previously tested another engine cold and it gave great figures.
What's your thoughts on drag pipes,fitted to a stock engine?
In short am I dreaming about avoiding a rebuild?
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Last edited by Big Nick; 10-07-2013 at 06:25 PM. Reason: Added symptom re ill health.
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post #2 of 26 (permalink) Old 10-07-2013, 06:43 PM
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You cant run open drag pipes on these bikes w/o causing damage....Im guessing fried valves....youre looking at least at a top end redo, IMO....I bet yer plugs were white....didnt even check em, did ya ?.....60k though, is a lot....rings may be in order as well.....I would.....clean and reseat the valves when ya do it....



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post #3 of 26 (permalink) Old 10-07-2013, 07:38 PM
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Do a leakdown test?
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post #4 of 26 (permalink) Old 10-07-2013, 08:02 PM
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...at 60k, is a leakdown really needed ?....especially if he aint the original owner....
My bike is 29 yrs old...and I get 135 psi out of the rear...the front is 20-70....70 adding oil....

....IMO, safer to just do a top end rebuild over the winter, and get another 60k outta it....Im doin one on mine this winter.....rings, gaskets, seals and lappin in valves....thats it.....$100 or less in parts....



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post #5 of 26 (permalink) Old 10-07-2013, 08:31 PM Thread Starter
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Cheap Rebuild Wolfie.

I've been pricing parts in my reach and it seems, $100 per cylinder with my labour is about the cheapest it can be done, and thats conservative. You must have a good parts supplier Wolfie? Any suggested parts suppliers?

Last edited by Big Nick; 10-07-2013 at 08:36 PM. Reason: one more question.
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post #6 of 26 (permalink) Old 10-07-2013, 08:46 PM
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....just for rings and valve seals ?.....wow....and yeah...a buddy has a custom shop I get stuff thru...about 20% less than elsewhere ....I throw him some gamemeat when I get it....mebbe yer not looking in the right place online ?....for rings/seals, try a local dealership...by time you deal with PayPal overheads and shipping, it works out less....really.....not for all, but for many items....example....a speedo cable was $10 plus shipping on EBAY....I got it at my dealer for $12 and saved the $6 shipping.....dig ?....unless its a "special" part, like a side cover, try your local dealer first....dont forget too, that many of the same parts were interchangable thru years, models, and even brands.....example....a VN750 oil filler cap fits a 15 yr newer VN800 Drifter....thats how the Japs roll....thats how they make money, and can offer bikes at a lower price....they use the SAME parts for numerous applications....the CVK34 is a perfect example.....used from bikes, to watercraft, to snowmobiles, to dirtbikes....all different makes.....seartch outside the box....search the actual part numbers instead of on "Bikebandit" and such for VN specific....usually part numbers remain the same....
EN454 starter is the same as a VN750 starter....etc.............



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post #7 of 26 (permalink) Old 10-07-2013, 11:04 PM
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You could re-check the compression, then oil the cylinders and check it again, if the numbers go up a lot, you've got bad rings.

I think if the valves were burned, you'd be looking at near zero compression.

Leakdown test would show if the valves were leaking. Wouldn't need any specific percentage numbers, just air it up and listen.

Either way, it looks like at least the heads will need to come off.

But... If the timing chains were off the marks, that could drop the compression too.

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post #8 of 26 (permalink) Old 10-07-2013, 11:15 PM
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60,000km is about 32,000 miles, I'm betting on burnt exhaust valves especially with drag pipes which always raise exhaust temps. Might get away with a good hand lapping on the valves. still, since you're in there you might as well pull the cylinders and replace the rings.

Sprockster's suggestion about using some oil in the plug hole to test the rings is a good idea and easy to do. put about 1/6 oz (not too much) of motor oil in through the plug hole and test on one cylinder. then try the other cylinder. The oil will help seal leaky rings for a few seconds, maybe up to a minute of cranking. If pressure is up more than 10 psi the rings are probably worth looking at but I'd suggest the valves are the primary problem. Most spray oils sprayed in are too thin to do a good job sealing leaking rings so use some motor oil.

A longshot would be the valve timing for both cylinders having skipped a bit from a broken valve chain tensioner allowing the timing chain to jump but since both cyllinders are reading about the same this is doubtful. It's highly unlikely that both chains would have jumped the same number of teeth.

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Last edited by Spencer1; 10-07-2013 at 11:38 PM.
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post #9 of 26 (permalink) Old 10-08-2013, 01:30 AM Thread Starter
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Thanks for the feed back folks, I think it's time to role up the sleeves and go to it. If I'm going to lift the heads, I may just as well re-ring it. One positive is when it's done I'll have some confidence in it. Once again thanks all, your a knowledgeable bunch.
Rare in to days world.
Ps To Wolfie, I had some fresh Venison recently,MMMM. Lean tender and fresh.
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post #10 of 26 (permalink) Old 10-08-2013, 07:17 AM Thread Starter
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Update on the parts cost.I took Wolfies advice and rang my local parts shop.
The damage is $265, thats a pair of base gaskets,head gaskets,the guide seals,and piston rings for 2 cylinders. One stop and they'll be here in a month.
No hurry, I can spend the time on a bit of detailing.
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