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11 Brute 750 was smokin quite a bit and missing real bad. Pulled rear plug and it was loaded with oil sludge. Pulled exh pipe and found oil residue. Figured it was bad valve seals. Replaced all 4 seals on the rear cyl. Used pro x seals. Re assembled and still getting lots of smoke and oil on the plug. I didn’t pull the head to put new seals in. Any advice? I can’t figure out how to post a pic.
 

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11 Brute 750 was smokin quite a bit and missing real bad. Pulled rear plug and it was loaded with oil sludge. Pulled exh pipe and found oil residue. Figured it was bad valve seals. Replaced all 4 seals on the rear cyl. Used pro x seals. Re assembled and still getting lots of smoke and oil on the plug. I didn’t pull the head to put new seals in. Any advice? I can’t figure out how to post a pic.

Well if it's not the valve seals it has to be rings or piston. Do a leak-down and compression test to see. Unless what you think is oil is actually coolant...and if so it's probably a blown head gasket.
 

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Yeah I’ll try a leak down and see what happens. Oil level was low. Coolant level hasn’t dropped.
Any idea what a compression test should normally be? Thanks!
 

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Yeah I’ll try a leak down and see what happens. Oil level was low. Coolant level hasn’t dropped.
Any idea what a compression test should normally be? Thanks!
Book says with the compression releases working correctly. both plugs out and using the starter cranking at 300RPMs it should be in the 66psi area but I have seen then closer to 80 on a good engine. Below 40 is a problem.
 

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Discussion Starter #5
Book says with the compression releases working correctly. both plugs out and using the starter cranking at 300RPMs it should be in the 66psi area but I have seen then closer to 80 on a good engine. Below 40 is a problem.[/QUOTE


cool. Thank for the info! whats a good "reasonable" source for cyl and head repair?
 

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Book says with the compression releases working correctly. both plugs out and using the starter cranking at 300RPMs it should be in the 66psi area but I have seen then closer to 80 on a good engine. Below 40 is a problem.[/QUOTE


cool. Thank for the info! whats a good "reasonable" source for cyl and head repair?

I get all my parts from Cheapcycleparts.com
 

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Discussion Starter #7
Ok, now I’m really confused. 90 psi on compression test. Leak down test holds 45-50 psi with no leakage anywhere??!! With a breaker bar I moved piston up and down a bit with air in cyl - nothing!
 

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Ok, now I’m really confused. 90 psi on compression test. Leak down test holds 45-50 psi with no leakage anywhere??!! With a breaker bar I moved piston up and down a bit with air in cyl - nothing!

So on TDC, no air leaked out of either the intake valves or exhaust valves and only minimal through the rings..ie with the dip stick out just some minor sound..right? Have you checked under...or inside the air filter where the crankcase vent is to see if there is any sign of oil tracking down to the intake? That usually goes to the front cylinder though.
 

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Discussion Starter #9
Yeah. Tdc is completely silent thru intake and exh. No trace of oil in air box or throttle bodies. Oil level was low. I did leak down again with 75 psi and there is air in the crankcase. Not a lot. But a hissing. Pulled rad cap also, no bubbles. Guess I’m gonna pull the cyl and have a look. Little frustrating knowing there is no real suspect. Maybe a small score in the cyl wall??
 

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Discussion Starter #10
Pulled head. Nothing abnormal. Top of piston is clean. Valves have just a little build up, nothing major. Cyl wall is smooth as can be. Guess I’ll keep going and pull cyl, see if a ring is cracked?
 

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Pulled head. Nothing abnormal. Top of piston is clean. Valves have just a little build up, nothing major. Cyl wall is smooth as can be. Guess I’ll keep going and pull cyl, see if a ring is cracked?
I think if you had a broken ring it would have leaked more. Valve seals would have to be pretty bad or even gone to get enough oil to foul a plug. Baffling for sure.
 

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Discussion Starter #12
Yeah, I’m stumped. I might just throw a set of rings in it and see what happens. I’ve inspected all I can even with a magnifying glass. Nothin... In this case I’m kinda happy it’s the rear cyl. Motor is still in the quad. Not too bad coming apart or going together.
 

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Sub'd to see if you figure this out.
 

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Discussion Starter #14
Not yet. I pulled the cyl off and the walls are perfect. I checked the ring gaps and they are at the upper end of the measurements. I took the exh valves out of the head and did the "wobble check". I dont have a dial indicator to set it
up properly, but i get about 1/2 a mm movement on both valves. Intakes dont move hardly at all. I put the head in the parts washer and cleaned all the black tar like oil that was burnt in the exh port. At this point, I think im gonna send the heads out to get new exh valve guides and valves, replace piston and rings and keep fingers crossed. Bike has 700 miles with 130 hours. Pretty frustrating. I tried to post a few pics - couldnt figure how to do it from my ipad so i got on my pc.
 

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Discussion Starter #17
i spoke to one of the guys at BP Racing about the valves being a little wobbly in the guides, he didnt seem concerned. Really stumped here... Gonna mic up the cyl today and make sure thats in spec.
 

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The lack of coking on the exhaust stems says it not valve seals there and the clean coating on the intake stems also says they are also not flowing, however the perfect coating on the intakes do indicate that during scavenging, they are getting a puff of oil smoke and the wet build-up around the exhaust seats and down the port says it's being pumped-in in and uneven spray.. and run for periods with the plug fouled. The thick buildup on the plug says it's entering in high concentrations and not mixing well with the fuel.. so.... its entering the combustion chamber...and that's only by rings or bu a cracked piston. Take a very close look at the piston...from underneath too. Also take a close look at the oil tube that takes oil from the case to the head and the head gasket in that area.
 

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Discussion Starter #19
i inspected the piston and found no defects , head gasket was solid when removed. the oil tube seemed solid, i didnt really pay much attention to that but ill inspect it when I get home. I mic'd up the cyl in a few different spots. average reading is 3.3470". Book says standard is 3.3462 ~ 3.3467 with a service limit of 3.350 soooo that tells me i am .003 away from service limit. I may as well put a cyl, piston and rings on it. I spoke to billy at REVS Cycles, he seems like a good guy. He suggested a cyl as well. I asked him about doing both and he said being such a low time machine his opinion was to just do the one.
 

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i inspected the piston and found no defects , head gasket was solid when removed. the oil tube seemed solid, i didnt really pay much attention to that but ill inspect it when I get home. I mic'd up the cyl in a few different spots. average reading is 3.3470". Book says standard is 3.3462 ~ 3.3467 with a service limit of 3.350 soooo that tells me i am .003 away from service limit. I may as well put a cyl, piston and rings on it. I spoke to billy at REVS Cycles, he seems like a good guy. He suggested a cyl as well. I asked him about doing both and he said being such a low time machine his opinion was to just do the one.

Yeah I concur.
 
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