Ben TR250 Posted March 21, 2022 Report Share Posted March 21, 2022 For the first time since it arrived in Europe in about 1990, I have the head off my TR250 (no-emission equipment, running on 2 x HS6, also, I think with a fast road cam). It seems to have been skimmed and ports polished at some stage when it lived in Fresno. Actual head thickness is 3.457". According to the Moss catalogue the standard thickness is 3.4375". See table below. On the next page of the Moss catalogue for European users it recommends skimming US spec heads by about 0.100", to end up with 3.375" (to raise compression ratio to 9.5:1). This would seem to suggest standard thickness should be 3.475". Can anyone say definitively if the data in the table is a mis-print? On a similar theme, if I skimmed to the suggested 3.375" would I need shorter push rods? Moss seem to offer push rods from 7.99" to 8.30". Current length is 8.1" so I would only gain 0.1". Unfortunately I don't know the cam specification, but there always seemed to be plenty of space for tappet adjustment. Many thanks in anticipation of some much needed wisdom from someone whio might have been down this road. Quote Link to post Share on other sites
Kenrow Posted March 22, 2022 Report Share Posted March 22, 2022 (edited) Two good resources on cylinder heads are Richard Goode (https://www.goodparts.com/tr6-compression-ratio/) and Chris Witor (https://www.chriswitor.com/technical.php) Your chart seems to have quite a few errors if I’m understanding what they call overall thickness. Edited March 22, 2022 by Kenrow Added info Quote Link to post Share on other sites
Ben TR250 Posted March 22, 2022 Author Report Share Posted March 22, 2022 Thanks Ken, for these helpful links. Moss agrees that there are errors, and will correct in a future additon. They were also kind and consulted a workshop which had done this conversion, and found 3.416 gave the desired compression ratio of 9.5:1. I will need shorter push rods, but not a problem. Thanks again. Happy motoring Ben Quote Link to post Share on other sites
Kenrow Posted March 23, 2022 Report Share Posted March 23, 2022 I believe the 8.1” push rod length is the standard length rod for the 9.5 CP TR6’s. Quote Link to post Share on other sites
Kenrow Posted March 24, 2022 Report Share Posted March 24, 2022 Do not forget if your combustion chambers have been modified you will need to take that into account in your head thickness for a given combustion ratio. Quote Link to post Share on other sites
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