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Original Message
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| RE: 390 piston rings |
| By John - 03/14/2005 9:46:35 PM; IP 142.177.12.69 |
| Seems to me Hastings asks for 0.004" of gap clearance per inch of cyl bore....so 0.016" would be good (at least for the top ring...second ring can be more....oil ring doesn't matter too much). Yours are approx twice that. The specs are on the Hasting box or wrapping paper for the ring or somewhere with the ring set paperwork. The ring must be square in the cylinder bore for measuring gap clearance. Down a bit is wise in case the top of the cylinder isn't machined quite right....too dificult to explain in few words. Put the ring in the bore and using a piston, push it down about an inch. Remove piston and use feeler gauge to check. You probably have done all this correctly, so not sure what else there is.... You are sure the rings arn't a stock set, or for 0.030" over vs 0.040" over? I didn't do the math, but it may work out to that....i.e. wrong rings. About the piston to cylinder wall clearance.... A lot of the TRW forgings call for very tight clearances these days...amazing really. TRW usually suggest adding 0.001" of clearance for a performance enigne. If you allowed for this and still think it's tight, keep in mind the piston skirts will deform in slightly after the break-in....adding about another 0.001" of clearance. So take it easy for the the first drive and you should be fine after that...er..once you get the ring situation cleared up, of course. Measuring cylinder to piston clearance is tricky. Machine Shops use a micrometer, but using an inside micrometer, or those telescoping aids that work with an outside micrometer are tricky. You never can be sure if you are measuring across the 'exact" center or not. Feeler gauges work, but as they have to bend across the blade, getting a "feel" for the right guage and clearance takes practise. |
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This thread, so far...
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