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FYI, Grom compression and Temp, pic

9533 Views 7 Replies 6 Participants Last post by  pwr2wh8
[HR][/HR] The Grom has less than 200 miles on the odm and this morning I decided to check the compression since the my adapters for my compression tester came in and I did not have a small 10 mm spark plug adapter.

I checked the compression with both of my testers and I got between 100-105 psi with a stone cold engine with no warm up.

setting up the test with my old tester

second tester reading 100-105psi

testing heat on the exhaust, heads and cylinder, warmed up the engine a bit

head temp around 160-171 deg F

cylinder temp 160-180 deg F WOT

exhaust temp taken from the pipe leaving the head 311-337 deg F WOT
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Don't panic about the compression. It's about 160 PSI stock. The Grom has a ACR,(automatic compression release) on the exhaust rocker. Spinning the engine activates the weight on the cam and opens the exhaust valve just slightly. I don't know why they don't mention it in the shop manual. Using an intake rocker on the exhaust fix's the issue, and you get 160 PSI. It's there for starting.
I wonder if that's the reason why the exhaust has a different sound during cold start and once it's built up some heat, the exhaust sound changes?

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