750mors
Been Around the Block
Hi Guys and Girls,
Bear with me, the questions are below, but I want to share the background to help those reading picture the scenario.
I'm in the final stages of my CB750 DOHC build and have come up against something that I can't get my head around. So I thought I'd throw it out there and see if anyone can share their thoughts on the matter.
Firstly, my engine is freshly rebuilt. Bottom end by me, and the head work externally. I haven't had this engine running since and have just started the task of carrying out all the pre-checks over the past week.
Being completely honest, the first hurdle was completely my fault, I had the cams incorrectly timed. So having rectified that, my compression gauge turned up in the mail and I threw that on and realized I also have a dead No. 3 cylinder with zero compression. The other 3 are good with readings of 105 - 130psi.
I then checked the valve clearances and found that the Inlet on No. 3 has been set up to 0.6mm (.023") instead of 0.06mm (0.0023"). The exhaust on 3 and the rest are a little tight but consistent.
Could this be the cause of the zero compression?
My first thought was that naturally it must be if it can't get air in it has nothing to compress, however, looking through the plug hole I can see that the Inlet valves are still opening (albeit .54mm (0.021") less).
Would this much excess clearance be enough to not lift the valve off the seat?
Needless to say I need to remedy the clearances, which will answer my question. But while I'm waiting on a valve shim tool to arrive from the U.S. I wanted to hear from the greater DTT community and see what you all had to say.
Thanks for reading.
Matt
Bear with me, the questions are below, but I want to share the background to help those reading picture the scenario.
I'm in the final stages of my CB750 DOHC build and have come up against something that I can't get my head around. So I thought I'd throw it out there and see if anyone can share their thoughts on the matter.
Firstly, my engine is freshly rebuilt. Bottom end by me, and the head work externally. I haven't had this engine running since and have just started the task of carrying out all the pre-checks over the past week.
Being completely honest, the first hurdle was completely my fault, I had the cams incorrectly timed. So having rectified that, my compression gauge turned up in the mail and I threw that on and realized I also have a dead No. 3 cylinder with zero compression. The other 3 are good with readings of 105 - 130psi.
I then checked the valve clearances and found that the Inlet on No. 3 has been set up to 0.6mm (.023") instead of 0.06mm (0.0023"). The exhaust on 3 and the rest are a little tight but consistent.
Could this be the cause of the zero compression?
My first thought was that naturally it must be if it can't get air in it has nothing to compress, however, looking through the plug hole I can see that the Inlet valves are still opening (albeit .54mm (0.021") less).
Would this much excess clearance be enough to not lift the valve off the seat?
Needless to say I need to remedy the clearances, which will answer my question. But while I'm waiting on a valve shim tool to arrive from the U.S. I wanted to hear from the greater DTT community and see what you all had to say.
Thanks for reading.
Matt