Dazed and Confused

I rebuilt my 76 900 motor last winter bored to 1015,
new rings, head (ebay buy) checked by local shop,
they said it was fine, finnally get it togeather and NO compression on #3 NOT ANY PERIOD. Oil down the plug hole NO change. Compression checked just by putting thumb over plug hole. Lost my comp tester to thief:angry:
I can see the valves and they look good (thruogh the plug hole) Pulled cover today and cams and buckets look
good. #3 exhaust bucket rotates when turning over with
kick lever and can spin the bucket when lobe is away from shim, valve clearances may be a little tight over all .03mm on that shim. Changed coils on that cyl. no change,
Changed carbs from 29 smoothbores to 26s still no
change
Help $$

Sounds to me like you have a valve that is either not seating properly or its not closing all the way like your valve lash is to tight

Not to be ignorant, but someone may have forgotten to install the rings????? on that cylinder.

if you have a air compressor, you can set the motor so the valves are colsed on that cyl, put it in gear to hold the motor so it wont turn over, and blow air into that cyl to see where it goes. Then make a plan on what needs to be done.

As stated above clearance is about .03mm Yes a little tight but I can spin the bucket with my finger Any one know of a way to clean the valve seat without pulling the head.

And I know I have all rings installed.
Okatar you forgot the :laugh: after your post :laugh: :laugh:

I useed to have a plug insert for an air compressor it vanished with my comp. tester:angry:
Thanks guys to bad the weather here is getting cold now may not get to it till spring I dont want the cylinders open to a moist garage all winter

No...no...no! You started this thread so now you have to finish it! You can't make us sit here at our computers waiting til spring to find out what it was. You MUST finish this! OH...I forgot!:blush: :laugh:

Id love too 50 today 34 by THANKSGIVING

did this motor ever run?...how did you find out #3 had no compression?.....no pro, but it sounds like the e-bay head might be suspect.......interesting........

moneypit:
When assembling the engine, was it possible that the camshafts were out of time with the crankshaft, and the engine rotated somewhat? If this bent a valve on #3 cylinder, then you could have clearance between the bucket and the cam, but the valve would not be sealing at all, but still consistently closing. Did you have to change shims drastically for cylinder #3?

Do like BSKZ650 suggested and use compressed air to see where the leakage is going. Hope the weather allows you to do the work and not wait until winter is over. Good luck.

moneypit wrote:

I rebuilt my 76 900 motor last winter bored to 1015,
new rings, head (ebay buy) checked by local shop,
they said it was fine, finnally get it togeather and NO compression on #3 NOT ANY PERIOD. Oil down the plug hole NO change. Compression checked just by putting thumb over plug hole. Lost my comp tester to thief:angry:
I can see the valves and they look good (thruogh the plug hole) Pulled cover today and cams and buckets look
good. #3 exhaust bucket rotates when turning over with
kick lever and can spin the bucket when lobe is away from shim, valve clearances may be a little tight over all .03mm on that shim. Changed coils on that cyl. no change,
Changed carbs from 29 smoothbores to 26s still no
change
Help $$

NO compression on #3...#3 exhaust bucket rotates when turning over with kick lever and can spin the bucket when lobe is away from shim....

What about the intake clearance? Is there at least some minimal clearance on intake #3? Just wanting to confirm.

Would consider taking a ride "on three cylinders" with idea of possibly blowing away any carbon speck that might be interfering with complete seal of a #3 valve seat.

Am also wondering whether the local shop was correct when opining that the head was fine. Was each valve checked to assure it fully sealed in the seat when closed?

Good Luck!

keith1 wrote:

did this motor ever run?...how did you find out #3 had no compression?.....no pro, but it sounds like the e-bay head might be suspect.......interesting........

It ran 15 years ago Ive owned it since 83 parked it because its hard to take the kid to daycare?school on it:laugh:
Had it running thought it was carbs when noticed cold pipe
checked spark OK changed carbs still cold pulled plug and put thumb over plug hole and kicked it and NO compression:angry:

WABBMW wrote:

moneypit:
When assembling the engine, was it possible that the camshafts were out of time with the crankshaft, and the engine rotated somewhat? If this bent a valve on #3 cylinder, then you could have clearance between the bucket and the cam, but the valve would not be sealing at all, but still consistently closing. Did you have to change shims drastically for cylinder #3?

Do like BSKZ650 suggested and use compressed air to see where the leakage is going. Hope the weather allows you to do the work and not wait until winter is over. Good luck.

I took pics of cam timing could post but that would mean multiple pic post dont have photobucket account yet it all looked good