Topic: cb750 engine flush?

[orkid1989]

i was wondering if i could do an engine flush on my 71 cb750? the problem is that i do an oil change on the bike and it is instantly (less than 20 miles) jet black and i am getting tired of changing the oil constantly. but i also heard that it might be bad for the clutch and stator. any ideas anyone?

[MCRider]

i was wondering if i could do an engine flush on my 71 cb750? the problem is that i do an oil change on the bike and it is instantly (less than 20 miles) jet black and i am getting tired of changing the oil constantly. but i also heard that it might be bad for the clutch and stator. any ideas anyone?

Won't hurt the stator in my mind. May cause the clutch to slip a little while its in there. May not.  But just ride it for 20 to 50 miles and change it out. I'd use SeaFoam. From the auto parts stores.

[Bob Wessner]

What's the tune-up history? Sounds like it may be running too rich.

[orkid1989]

i was wondering if i could do an engine flush on my 71 cb750? the problem is that i do an oil change on the bike and it is instantly (less than 20 miles) jet black and i am getting tired of changing the oil constantly. but i also heard that it might be bad for the clutch and stator. any ideas anyone?

Won't hurt the stator in my mind. May cause the clutch to slip a little while its in there. May not.  But just ride it for 20 to 50 miles and change it out. I'd use SeaFoam. From the auto parts stores.

o ok i was thinking about possibly using an engine flush from amsoil  but seafoam should do the trick too. should i use a heavier oil like 20-50 with one can of the seafoam or just stick to the 10-40? my friend also mentioned something about adding a little transmission fluid to clean out oil in his car. would that work or just do more damage than good?

[Stev-o]

I would not put ATF in my motor.

[orkid1989]

What's the tune-up history? Sounds like it may be running too rich.

well i just fully rebuilt the carbs and added 130 jets because it was running lean with 120. i also replaced the spark plugs and wires about 300 miles ago (a little over a month ago). i have also checked and adjusted the valve clearance and timing about 100 miles ago. ive done more but i just cant remember at the moment. i think the last guy that had the bike (i bought it in august) probably rarely changed the oil so engine is full of deposits

[orkid1989]

I would not put ATF in my motor.

would probably destroy the clutch?

[mycb750k6]

I'd look in the oil tank for sludge. Mine was filled at the bottom 1/4" thick which polluted the oil after the first run of an oil change.

[orkid1989]

I'd look in the oil tank for sludge. Mine was filled at the bottom 1/4" thick which polluted the oil after the first run of an oil change.

o ok good idea. did you just take it off and clean it with brake cleaner or something?

[Bob Wessner]

What's the tune-up history? Sounds like it may be running too rich.

well i just fully rebuilt the carbs and added 130 jets because it was running lean with 120. i also replaced the spark plugs and wires about 300 miles ago (a little over a month ago). i have also checked and adjusted the valve clearance and timing about 100 miles ago. ive done more but i just cant remember at the moment. i think the last guy that had the bike (i bought it in august) probably rarely changed the oil so engine is full of deposits

If that's case it might be worth pulling the oil tank and dropping the pan. If it is accumulated gunk, you'll likely find it there and can clean it out.

[orkid1989]

What's the tune-up history? Sounds like it may be running too rich.

well i just fully rebuilt the carbs and added 130 jets because it was running lean with 120. i also replaced the spark plugs and wires about 300 miles ago (a little over a month ago). i have also checked and adjusted the valve clearance and timing about 100 miles ago. ive done more but i just cant remember at the moment. i think the last guy that had the bike (i bought it in august) probably rarely changed the oil so engine is full of deposits

If that's case it might be worth pulling the oil tank and dropping the pan. If it is accumulated gunk, you'll likely find it there and can clean it out.

o ok. ill have to try that

[mycb750k6]

Yeah I removed the oil tank and used solvent in the oil tank to get all the sludge out but it took a few cleanings to get it completely clean.

[BobbyR]

I would not put ATF in my motor.

would probably destroy the clutch?

The opposite, dirt racers use ATF on new clutch plates to give them more grip. Most engine flush products are mostly kerosene.

[orkid1989]

ok well last night i removed the oil tank, removed oil filter, dropped the pan, removed oil pump and i cleaned all the crud off of the parts and their surprisingly wasnt too extremely dirty (it wasnt spotless either though) but i think i found what appears to be a large chunk of a piston ring i havent gotten around to flushing it out yet but i will try it today. when i flush it can i use car oil instead of motorcycle oil because it is alot cheaper and i bought the last 7 quarts of motorcycle oil from the auto parts store?

[KingCustomCycles.com]

Not surprising, black oil is from combustion blow-by which is carbon deposits and overheated oil blowing downward past the rings into the crankcase during operation.  It is not all that troublesome that your oil turns black quickly, it just means you have somewhat worn rings, scored cylinders, or other leakage problems.  I would suspect the ring piece is the problem although it may be a combination of wear and the broken ring.  Either way, pull the cylinders, hone and inspect the bores, and replace the rings.  It is not all that difficult or expensive. 

[orkid1989]

Not surprising, black oil is from combustion blow-by which is carbon deposits and overheated oil blowing downward past the rings into the crankcase during operation.  It is not all that troublesome that your oil turns black quickly, it just means you have somewhat worn rings, scored cylinders, or other leakage problems.  I would suspect the ring piece is the problem although it may be a combination of wear and the broken ring.  Either way, pull the cylinders, hone and inspect the bores, and replace the rings.  It is not all that difficult or expensive. 

sounds alot easier said than done but ill try. i was just considering getting a cycle xchange engine kit and doing a full rebuild and bore to 849 because i am having to remove and take apart the engine anyways

[KingCustomCycles.com]

The top end is much easier than doing the whole engine and transmission.  It is almost fun compared to the low end.  I had an 836 kit in one with proper jetting and sprockets would pull the front tire a few inches off while spinning the rear.  Much fun. Enjoy.

[orkid1989]

well i just pulled the engine and damn that was hard. i will have to take it apart tomorrow and check the cylinders but i know i am going to atleast need new rings but due to the age of the engine and know idea how the cylinder walls look i might need to get new pistons. i was wondering if the cycle x 1st over piston kit with cams and gasket for $460 would be good?

[Stev-o]

orkid - click here ----->>  http://forums.sohc4.net/index.php?topic=77080.0