spare cylinder block

I have a 1978 kz650 and replaced the gaskets on it today due to an oil leak. I replaced all the gaskets but against intuition i also replaced the cylinder block with a spare one that i had from a parts bike because it seemed to be in better shape (no broken fins....)
Well got the bike back together and it seems as though i have no compression on cylinders 1 and 2... 3 and 4 look ok though.
Was this a dumb move replacing the cylinder head or do i have another problem which is causing compression issues?
Ran fine before hand... other then the oil leak and i am pretty sure my timing was good....

thanks for all help will be appreciated!

You say you replaced the cylinder block, but you then ask if replacing the head was a bad idea.

Replacing block without checking to make sure the bore is within limits and without using new rings after honing is a bad idea.

Replacing one head with another "good" head is usually not a problem.

Which part did you replace?

sorry about the confusion... i replaced the cylinder block from a donor bike.... i guess i will have to go back and switch them back out...
checked compression and I am getting 0... i wouldnt have thought that the bore would have been that far off...

The only way a piston and rings can cause zero compression is if they aren't there, even a piston with no rings will show at least a little compression.

It's still a bad idea to do that though

First the basics.

Throttle held wide open (or carbs removed) during test?

Did you repeat the measurements to make sure that zero was correct?

Are you absolutely certain you installed the cams correctly?

Did you feel a "clunk" in the motor when you first turned it over after reassembly?


It would be a real good idea to put the original block back on the motor, and check for bent valves while you have the head off.

If you have zero, you probably have bent valves. Don't be turning the motor over anymore until you have deone a leakdown test.

Jay

well... damn.
I have set the timing a couple times and thought i had it on the dot... checked cylinder 1 and got 0 compression.
thought the compression gauge may have been off and checked 4 and got about 120. will do some work tomorrow and try to find the problem...
will follow up as soon as i can... or be calling ape to get some quotes.

Steve Elliot wrote... even a piston with no rings will show at least a little compression...

HOW DO YOU KNOW? bwhahahaha

wiredgeorge wrote:

Steve Elliot wrote... even a piston with no rings will show at least a little compression...

HOW DO YOU KNOW? bwhahahaha

I used to run a vehicle maintenance shop in the USAF, amazing the things that some of my guys would forget to put in a motor during a rebuild (and some of the tools they would leave inside it). 1/2 rod bearing shell, piston rings, etc, I listened from my office when they would first start a motor after a rebuild, and could usually tell them what parts to look for in their toolboxes that they had left out

Well.... pretty good news.
Replaced the cylinder block with the original... and everything looked good physically... cosmetically is another story but..

Got good compression... about 140 across the board but but when i fired her back up i noticed that the exhaust pipe on cylinder 1 wasnt getting hot. I also noticed a rapid clink coming from the valve cover. I have a manual cam chain tensioner and it looks good. Air is coming out of the pipes so... maybe its not firing or could the *clink* be coming from the intake valve?

At least I got her back on her feet.... hopefully i can pinpoint this little matter.

Thanks again guys!

EDIT: checked it again and all the pipes are smoking hot... except 1.. and I have spark ....

have you checke the valves, may need some adj