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I need help figuring out the cause of some issues on my bike. It's a 1983 Xr600r I just finished putting a big bore kit in it (102mm JE high comp piston) and new sleeve and a new used cylinder head after a broken valve took out my piston. It runs at low throttle input fine however when I get to the top of my rpm range, change throttle position quickly, or change gears under hard acceleration it will suddenly make a loud thunking noise that sounds like it's coming from the head or valve cover left side. Then continue to run fine. Once warmed up it would puff out clouds of thick white smoke from the left side of the engine near the head gasket immediately in front of the XR cover on the head as well as leaking oil. Could this simply be a blown head gasket? All the gaskets were replaced less than 10 miles ago before I attempted to break in the new piston. It is also backfiring when I let off the throttle. Pulled the spark plugs and it is dry and white on the electrode.

Edited by Oregonthumper

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I gotta ask,,did you replace the cam chain,the tensioner and pin and spring??????

valves don`t break off usually,,the timing jumps and they are assaulted by the piston and snap off..

 

Was the rod checked for bad lower bearing/thrust washers..????????/

 

I`m wondering if you are going to repeat that again..

 

give us a list of parts you  changed..

 

 

B

Edited by brianhare
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Replaced piston, rings, wrist pin, complete head off fleabay, all the gaskets in the top end, overbore sleeve did not change the tensioner, or chain. The valves still had some freeplay at TDC after riding but I did not actually stick a feeler guage in and check the clearance properly. 

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Could you see valve clash in the relief areas on the old piston....or was the piston destroyed..

 

the oil leak will be easy to find,,,the noise is what concerns me..

 

B

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The old piston was completely destroyed. The valve came off, rattled around in the cylinder destroying the head as well and eventually embedding itself in a hole in the piston. The other 3 valves were fine though minus the valve seats getting a little roughed up

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On 9/4/2017 at 1:59 PM, brianhare said:

Could you see valve clash in the relief areas on the old piston....or was the piston destroyed..

 

the oil leak will be easy to find,,,the noise is what concerns me..

 

B

Ok so I got the valve cover and head off today. No noticeable indication of the valve making contact with the piston.

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Sorry,,was out of town picking up a 87 Mustang GT 14.000 original miles,,that was an adventure..lol

 

So..i wanted to know if the valves were touching on the old piston,,so we would know if the timing jumped and possibly took that valve out,,since you see no marks in the pockets on the new piston then the timing did not jump this time,,at least not yet if that was even the original issue...

damaged old parts can tell a lot of tales sometimes.....that`s why I asked..

So.....did the crank check out good at rebuild,,no worn thrust washers,,,proper side clearances?????

So this year does not have the FIFTH valve for decompression I see???

ticking noises like valve adjustment and some rattles are not as concerning to me as actual clunk noises,,,solid clunks usually mean something is definitely not right and could cause big damage quickly,hate to see all your energy fixing it up not end well..

Without actually hearing the noise,,all I can suggest is check very closely,,at everything..post pics of anything you think is suspect..

 

B

Edited by brianhare
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#1 chains don't stretch, they wear. #2 from what your describing the bike sounds lean by the popping and unless you had the deck, cylinder and head milled it could be warped. Or the easiest, cheapest way is to replace the cylinder and head studs with good ones. Slot of people rebuild something and don't thing about the worn bolts or studs. It doesn't take much to lift a head on the cylinder if it's modified. #1 I'd pay the $100 or what ever for a couple dyno pulls to check the a/f ratio. If it's 13 or under then a lean condition isn't the problem. I'd start there.

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I need help figuring out the cause of some issues on my bike. It's a 1983 Xr600r


So..... there is no such bike. The xr600r was introduced in 85. I'm gonna guess you really have an xl600r.

As Brian said, it looks as though your replacement head does not have the 5th decomp valve (which a stock xl600r would have came equipped with). So, again I'm going to make a guess, did you buy either a newer Xl model head or an xr600r head? Either way the valves and ports will be smaller than the original 83 head and will be mismatched to the larger carbs on your bike.


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