paulg18 Posted February 24, 2021 Share Posted February 24, 2021 I have a Polini Thor 100 which has nearly 200 hours on it and as part of the 200 hour servicing it is recommended to replace the piston and rings. I currently have an 'A' size piston and am trying to establish what the most suitable size to order for replacement is. I contacted Polini who suggested measuring the bore to find the best fit but have as yet been unable to supply me with dimensional info. I have access to bore micrometers at my workplace so that's not a problem but I need to know the recommended clearance and pistons sizes form A to D. Does anyone have this information or any suggestions. Quote Link to comment Share on other sites More sharing options...
cas_whitmore Posted February 24, 2021 Share Posted February 24, 2021 If it was mine I’d replace with the A size again , assuming its running ok now and coating on your cylinder is not worn away, which would be a whole new ball game . Quote Link to comment Share on other sites More sharing options...
paulg18 Posted February 25, 2021 Author Share Posted February 25, 2021 I am inclined to do exactly that, it just makes it a bit of a nonsense to have four piston sizes to choose from and no dimensional criteria to aid in your selection. Quote Link to comment Share on other sites More sharing options...
cas_whitmore Posted February 25, 2021 Share Posted February 25, 2021 The different sizes aren’t what you think there for , A. B. C. D , etc are for manufacturing tolerances , so the same motor as yours from same production process will probably have a slightly different bore or maybe slightly thicker cylinder coating the chap selecting the piston will have a choice of pistons to select from , A. B. C. D parts bin , where the pistons are kept, hope it helps . Quote Link to comment Share on other sites More sharing options...
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