How To Tear Down The Head

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I_THUMP

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His motor was blowing smoke so he decided to pull the head off and check the condition or his rings and he tells me they were fine. Now that he has it all back together its still blowing smoke and has developed the rattling noise aswell lol. He hasnt done anything with valves so could that be the problem? What about the smokey motor?
 

Satchy

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the cam chain could also have something to do with the rattling motor... could b stretched or the tensioner mighten b working...
 

Cactus Jack

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Sources of white /grey / or blue smoke are :

1) Poorly sealing rings on the bore wall ie rings or bore worn out of round , honing peaks gone without rings bedding in ... bore wall or rings scratched or gouged by grit ... Rings can also be stretched out of round during installation or removal and they'll never ever seal again ... Even if rings are carefully removed from a bore ... the cylinder MUST be re-honed for them to re-seal to a high degree again ...

2) Ring end gaps too big ... Ring end gaps not properly staggered or in the wrong position in the bore ...

3) Oil can leak past worn , damaged or incorrectly installed valve stem oil seals ... the symptoms are usually a puff of white smoke on start up that goes away or diminishes as the engine warms up ... oil leaks into the ports while the engine is sitting ... but the leakage rate is too slow to make smoke while the engine is running ... The engine can puff white smoke when the throttle is backed off since the cylinder vacuum sucks hard on the seals when the slide is shut off ... The same can happen if the ring seal is bad too ... only the oil gets sucked up from the crank case ... Oil mist or smoke blowing out from the dipstick or vents can also indicate bad ring seal / blowby ...

3) Bore scuffed from over heating ... the rings expand , the ends butt tightly together , the ring keeps expanding and forces too hard on the bore scraping the honing off and glazing the bore ... then when the engine cools , the bore is bigger than the rings ... it only has to be a micro thou bigger to be no good ...

4) Those junk thin steel shim gaskets that are supplied with some BBK's combined with the removal of the rubber O-ring and trumpet piece can allow oil to leak from the gallery into the bore ... Once again , the oil gets sucked into the cylinder on backing off the throttle from high revs ... Only copper or stock type gaskets which expand or crush unevenly can fill variances in between machined surfaces ... For a steel gasket to work , the machining would have to be perfect ... and that's pure fantasy without hand scraping and lapping each individual cylinder head to the cylinder ... They say to use Honda bond or some other type of hardening gasket cement , but anything like that can be blown out or crack and leak ... The very idea of using it to do the job of a head gasket is ridiculous ... and BODGEY ...

5) Even IF the parts were lapped to perfection ... the tensions of each cylinder stud would all have to be precisely the same and torqued in the proper sequence to avoid distortion ...

Bad ring seal or a blown head gasket causes smoking to get worse as the engine revs higher ... The colour varies from grey to white as the amount of oil getting burnt increases ... Only a rich fuel to air ratio burns black ...

The rattling sounds like he's done something wrong on re assembly ... ie cam chain loose , cam to crank timing out and valves getting clipped by the piston , rocker to valve stem clearances too big ... Not enough clearance can also cause a valve to hit the piston IF the valve to piston clearances aren't right ... A valve being held off the seat or a bent valve can cause a ticking noise as gas pressure escapes past the valve seats ... or a detonation type noise (rattling) in the exhaust pipe ...

Countless other factors can also cause weird noises or smoking ... A relo of mine told me that his XR75 was idling great after he rebuilt it ... then it suddenly locked dead while idling ... When he pulled it down he found the cam sprocket had broken in half ... The time before THAT the cam chain had "jumped" causing the valves to hit the piston and bend ... Obviously it was cracked from before ... So IF an engine fails on you ... thoroughly inspect EVERY part involved for hairline cracks ... no matter how minor you think the blow up was ...
 

I_THUMP

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Cactus you are a champion!

I will tell him to give that a read. I'm thinking the rattle has something to do with the timing chain so the smoke will be his main concern now because it blows more smoke than one of those smoke machines you see at nightclubs lol. The smoke is white or a light grey colour.

Thanks for that Cactus, +++Reps for you ;)
 

arkark

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thats all good ,, but how do you get it back on ,, does the cam chain just go back on ,,or is there a special way to do it ???
 

Dabomb

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loosening off/removing the cam chain tensioner bolt makes it easier....its left of the oil drain plug.
also bolt down your head to the right tension in diagonal matter, before you put the cam chain and sprocket back on....from memory 10ft pounds of torque...
 

arkark

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hi ,, i just like 2 know >>>> how do i know if i am puting the cam cog on right ,, can it just go on any way or does it have line up to the cam timing marks ,,,,and if the cam chain had moved in the motor does it matter were it goes back on the bottom cog in the motor ???? thx 4 your time :)
 
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Dabomb

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hey

there are 3 cam bolts, they are UNEVENLY spaced, so it can only be bolted on one way!
the cam chain cant travel pass the the cam roller which is along side the cylinder on that small passage.
 

headsmess

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best stuff up i seen was my mates xr80... hands up who knows what a "ridge reamer" is for?

of course, rebuilt by a fully qualified mechanic....

shoulda seen the piston afterwards when i got my turn at doing the rebuild...whered that top ring go?

matter of fact, whered half the bottom ring go too? :p
 

Andrew Aslan

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thank you vewry much! lol we just searched all over google and youtube and you have finaly helped! cheers
 

Cactus Jack

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A ridge reamer is a special tool for removing the step that forms in the bore of a badly worn cylinder ... basically , if there's a step in a motorcycles' or ANY engines' bore it needs a rebore and oversized piston and rings ... Motorcycles especially need a tight piston to bore clearance to prevent piston slap since they can rev so high ... XR's will go over 11,000 rpm stock ... The results of excessive piston slap are usually a shattered piston ...
 

aspect 50s

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sum 1 should put up another 1 for those peaple who carnt do the top end rebuild becoz i had 2 learn by my self a few years ago how 2 do it and it aint that simple 2 start of with butn the pistn and the rings and that the 1st time u do it all if any 1nse got time on there hands 2 show all the freshies how 2 do it
 

DvDRip

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thanks for this mate, I just took off my head and barrel, I was a bit worried about taking it off at first but once you've done it you realize how bloody simple it is
 

splity

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hey mate sic post, is there a guide to putting it bak together from replacing piston.ive put it al together just dont know if igot everything rite
 

Cam

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do the 3 bolts holding the cam sprocket have to be torqued when you put the head back on?
 

wulliedey

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does the cam cover just pull off and glue back on as it looks tight thanx for any info
 

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