Alan Gallafant Posted June 8, 2019 Report Share Posted June 8, 2019 Can anybody help? What do the grading of bores Std G, big end Std LM, and liners / Pistons grade FGH signify. regards Alan Quote Link to post Share on other sites
Motorsport Mickey Posted June 8, 2019 Report Share Posted June 8, 2019 Give us a clue, what model are we talking about ? Mick Richards Quote Link to post Share on other sites
Alan Gallafant Posted June 8, 2019 Author Report Share Posted June 8, 2019 Sorry Tr2 Quote Link to post Share on other sites
Bfg Posted June 8, 2019 Report Share Posted June 8, 2019 (edited) 6 hours ago, Alan Gallafant said: Can anybody help? What do the grading of bores Std G, big end Std LM, and liners / Pistons grade FGH signify. regards Alan 'Std G' is I believe a term used on reconditioned engines, which I guess means 'standard grind' or similar to signify being within standard bore +/- tolerances, and therefore standard piston skirt clearance. 'Std H' would be a little larger (perhaps 1/2 thou" at a time) until it was deemed necessary to rebore to +010 . I don't know about 'big end std LM' but if actually referring to the big end, is again probably a code designating the journal's size before it gets to -0.10. Grades F, G, or H are designations I've seen referring to the width of piston ring grooves, indicating wear or manufacturing tolerance. What this has to do with liners I do not know. Edited June 8, 2019 by Bfg Quote Link to post Share on other sites
Motorsport Mickey Posted June 8, 2019 Report Share Posted June 8, 2019 Alan, The STD G and Big end Std LM sound like a variety of expressions used on the FRE ( Factory ReConditioned) small plates which are often riveted on top of the engine number plinth on the left hand side ( passenger) of the engine block. Whatever is shown there...ignore it, I've rebuilt over 20 of these 4 cylinder engines and several race engines and some 3 or 4 have had these plates with information on it...none of which corresponded to what was inside the engine. These engines are over 50 years old and the plates were probably riveted on within the first 3 or 5 years of life when reconditioned. Since then they are likely to have been reworked maybe a couple of times at least by owners in their own premises and the FRE plates will not have been altered and updated. The F,G,H grading of pistons and liners is usual " batch engineering" practice where thousands of these components are produced and as tooling becomes worn or the men in brown coats became careless and units fall outside the manufacturing tolerances, they are "streamed" into these various nomenclature batches and matched against the closest pairing component ie piston to liner. If you are breaking down or reconditioning an engine the only way is to manually strip the engine and measure and record the appropriate units as to dimensions and tolerances. Use an original workshop manual and take note of the running clearances written there, for info I've had standard liners jig bored to move up onto larger Pistons by asking the engineering shop to bore to the clearances shown, and mostly Pistons and liners have been bought and fitted as sets with the clearances preset. Mick Richards Quote Link to post Share on other sites
Alan Gallafant Posted June 9, 2019 Author Report Share Posted June 9, 2019 Hi Mick, thank you for the information. I am going to recondition the engine, new Pistons liners and regrind the crank so as you say all that coding can go out the window. Once again many thanks for the help. Regards Alan. Quote Link to post Share on other sites
Alan Gallafant Posted June 9, 2019 Author Report Share Posted June 9, 2019 Many thanks to Bfg. Quote Link to post Share on other sites
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