Feedback required - Yamaha 70CES Head off, carbon on squish and some detonation on #1

[foodie]

Hey guys,

Looking for some insights in to what you read into the pics of my head that I just removed from my Yamaha 70CES.

I see some detonation on the top cyl around the squish band. Also, that amount of carbon on the exhaust side normal?

Compression is 140psi on all 3, which is about stock. Stock fuel and ports.

Any insights would be appreciated - Was looking to shave the head a bit to lift compression but now see the detonation!

Photos: https://goo.gl/photos/edP39uCrM5tyYuTCA

Cheers,
Thomas

[foodie]

To add to that, the pistons look fine. Bought this from someone, was rebuilt only about 50hrs ago. Maybe the head is from a previous build...

[racer]

Carbon on the head is appears normal, the pistons show the engine to be running rich. I dont see the detonation you mention, what I do see is a gasket surface and cylinder bores that have more than 50 hours on them or ones that were not properly prepared during rebuild.

[foodie]

Thanks guys.

I put it back on and did a squish test - to the best of my ability (using some modelling clay). Looks like all positive squish.

Going to take .5mm off the head to bring it down and compression up.

Pics: https://photos.google.com/share/AF1QipPm_yQaB-3Dtyg8OAS4TzeRzB0udKQKbRGgVcSrjR2Jzyh_8vtLMtmp-HLCbY41cw?key=NWdsT2VicWpBd044c3FzLXJXRlBmT1pINVZmNy1R

Average outside rim measurement was 1.31mm and inside 1.45mm

Skimming 0.5mm off should bring that to 0.8mm and 0.9mm

Sound right?

[mattmak77]

I did a measurement recently on a 1987 Yamaha 70 head (factory stock) and the numbers look nearly identical to yours. Also, looking at your pics, looking at details of the head casting, that does not look like a CES head.. but I'm not 100% sure what a CES head should look like..

[RSWORDS]

Looks like that head shows the evidence of why it was rebuilt.