Compression is Gone, Help!

[telefunkin]

81 kz750 Ltd
4 Cylinder
DOHC

I took apart the top end to replace the old gaskets. When I put it back together I messed up and didn't get the timing right. I only realized this after trying to start it for 15 minutes and then going back to the manual.

I went back and fixed the timing, now it turns over and the plugs are firing, but there is just no compression.

I'm guessing that I've "fubar'd" the valves, but that's just a guess.

Anyone have any thoughts/tips/suggestions?

[Sev]

Make sure you got the valve timing right And then make sure you didn't slam a valve into the piston when you tried to crank it over before...

[MrShake]

Make sure you got the valve timing right And then make sure you didn't slam a valve into the piston when you tried to crank it over before...

+1

This is exactly what happened to my bike.

[telefunkin]

Make sure you got the valve timing right And then make sure you didn't slam a valve into the piston when you tried to crank it over before...

I have the camshafts aligned properly according to the manual. Is there anything else to check for? I've been scanning over the manual but haven't found any other references to adjusting the timing.

[Sev]

DOHC, chain driven?

Do you have the correct number of links between the intake and exhaust cam? Did you set the cams on TDC off cylinder one? Did you correctly replace the head gasket, then torque in the required pattern?

I'd pull the head back off and take a look at the valves. Chances are pretty good that trying to crank it over with the timing being out you managed to break or bend your exhaust valves.

If you've got a leakdown tester (I think they're worth about $100) and a compressor then you can do a leakdown test.

Set the piston to TDC on compression stroke, and have someone hold the crankshaft in place with a breaker bar. Hook up the leakdown tester and let her rip. The crank will try to spin outta your hands, so make sure that you're ready for it.

Then listen at the following places for a "wind" noise:
1) airbox - leak past intake valve
2) exhaust pipe - leak past exhaust valve
3) oil filler hole - leak past rings

[telefunkin]

So I finally got some time today to get back into this. I opened up the top end again and it looks like they did slam the pistons. The 4 valves on the intake side seem to be seated ok, but the 4 on the exhaust side are popped out by about 1/8th of an inch.

Am I going to need a valve spring compressor to remove these, or can I do this safely without them? Also, will I need to replace anything other than the valves?

[MrShake]

A Valve spring compressor is a good idea, and you can get one for a GREAT price at http://www.mikesxs.com

You might be able to get the valves out using a larger deepwell socket and a mallet. Just get the lifter buckets off and place the socket over the end of the valve spring cap. A good firm rap should compress the spring enough for the collets to come out. Just be carefull not to loose the collets. Or, better advice is to wait for a compressor.. ahha. Theres lots of info about valves at http://www.dansmc.com

I would say, as long as the pistons arn't damaged, the only other thing I would check would be the valve guides.

[Sev]

You'er going to have to measure the valve springs as well.

If you're replacing the valves you also need new valve seals, and new collets.

[telefunkin]

thanks for the tips