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Author Topic: No compression - help . . .  (Read 1293 times)

DVDitman

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No compression - help . . .
« on: June 16, 2008, 12:07:14 PM »
At the top of a long hill  (one mile, gentle grade, 60 mph), The Mighty Bullet (7,960 miles on odometer) stalled and would not re-start. Fuel good,  plug color good, spark present, no compression. Checked valve adjustment - okay. Decompressor does not seem to be sticking. Can't tell if it is a blown head gasket, or, hideously, a blown piston.
Any suggestions? Shop doesn't open 'til tomorrow (Tues.) so I have today to search for likely problems.

cyrusb

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Re: No compression - help . . .
« Reply #1 on: June 16, 2008, 12:22:18 PM »
Hole in piston? Can you hear, say in the tailpipe, where the compression is being lost?

cochi

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Re: No compression - help . . .
« Reply #2 on: June 16, 2008, 04:27:21 PM »
DVDitman, I had the same problem at 7,000 miles. The bullet was running perfectly it suddenly died and there was no compression. Have you decarbonized the cylinder head yet? It's recommended at about 6,000 miles. What happened with mine was that a piece of carbon flaked off of the cylinder/piston and planted itself on the intake valve seat. It wedged the valve open only a couple of thousandths of an inch. It was enough to lose compression. Usually if a piston fails you  get some warning, IE lots of preignition pinging. Like suggested, listen to the exhaust and intake. If you hear a hiss during  the compression stroke on the carb side, the intake valve is sticking open. If you hear it on the exhaust pipe side, the exhaust valve is sticking open.  The fix is pretty straight forward.  You will have to pull the head, remove the valves and clean up the carbon on the piston and cylinder head. If carbon is not the culprit, you may have burned a valve. However, this also usually will give you a bit of warning before it happens, IE popping threw the carb or exhaust. The guys in forum actually diagnosed the problem for me. I did  the job myself and it took me about 3 hours. This included lapping the valves.  Good luck! cochi

DVDitman

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Re: No compression - help . . .
« Reply #3 on: June 16, 2008, 09:17:16 PM »
Cochi - Thanks, I'm going to check that out ASAP. Did it affect the movement of the valve adjusters at all? Mine still spin as expected, with no up-and-down play.
-Dave

dewjantim

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Re: No compression - help . . .
« Reply #4 on: June 16, 2008, 09:22:52 PM »
Hey Dave, are you sure that that compression release is working correctly. Mine sticks sometimes. Happy thumpin', Dew.
If it hurts, you're not dead yet!!!!!

DVDitman

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Re: No compression - help . . .
« Reply #5 on: June 17, 2008, 01:27:18 AM »
Yeah Dew, as best I can tell the compression release is working correctly. Did do a compression test this evening: 60 lbs. - not good - looking for 100-120 lbs. Trying to detect a hiss/wheeze through the tail pipe - I don't know, I hear all kinds of hissing and wheezing: I can't tell what it all is. I guess it's time to haul it on in to the shop.
Thanks Folks!

cochi

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Re: No compression - help . . .
« Reply #6 on: June 17, 2008, 08:53:41 PM »
DVDitman, Sorry I took so long in getting back. When my Bullet lost compression, valve adjustment was not affected. Just had no compression. The upside to all of this is that the Bullet is stone simple to work on. The head can be removed with the motor still in the frame. Can't do that on Japaneses bikes! If you do the work yourself, be sure to get the hardened cylinder stud  washers sold by CMW. The factory ones are soft and tend to distort. This can make the head difficult to remove. As they distort, washer material gets pushed into the stud threads effectively locking the head on to the cylinder. I had to use a mallet and a piece of wood to tap the head off. Be sure to tap under the exhaust port and intake port. Take your time go back and forth. Avoid tapping the fins! They Will either bend or snap! Also, use a get a new head gasket. To make sure it doesn't  leak, I sprayed Permatex copper gasket sealer on to the new gasket. Retourque the head, set the valves. Then start her up, take her for a short ride to warm her up, let her cool down and retorque the head again. You should retorque it again in 500 miles. She should be good for another 7-8000 miles. The guys in the Forum and at CMW are great for back up. Good luck.cochi :D

geoffbaker

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Re: No compression - help . . .
« Reply #7 on: June 18, 2008, 01:44:38 AM »
I had the same problem when I bought my bike... at 5000 it was badly carbonized. Once cleaned up it ran fine. Running the engine too rich will bring on carbonization pretty quick... but luckily, cleaning it up is an easy job and you can do it all yourself.
When I opened up my head, I could see that the exhaust valve wasn't shutting fully.
Good luck! And buy the hardened washers! Also, be gentle on your  banjo bolts and on the rocker bolts... they are easy to strip.