I have a 77 340 exciter and the stock bore should be 2.360 and it now measures 2.362. Is this in good enough cond. or should it be bored over? Thanks Rich.
YAMMIEGOD3:16
Active member
SPLITTING HAIRS. I SAY RUN IT. 3:16 (yammie tony)
2 thoudandths is well within tolerance.
Yamaha Nutz
New member
run it .............but when talking yamaha speek in metric
WopOnTour
Member
Variables need to be discussed here IMO. A single measurement is difficult to interpret.How exactly was this measurement performed.Was this with an actual dial type bore gage? or telescoping gage? Or?? Do you know the resolution/precision of the measuremetn tool?rich said:
Where exactly on the bore was this measurement observed? near the top of the swept thrust surface of the bore I presume? Down bore somewhere? What about taper and out-of round? What about the other cylinder, was it exactly the same? (seldom the case)
In any case probably more important will be the actual piston clearance you have. So I would sugggest to now measure the new pistons at 90 degrees to the wrist pin about 0.4-0.5" up from the bottom of the skirt. Subtract the 2 measurement to determine the clearance and compare THAT to your published specs. (or that provided by the piston manufacturer if aftermarket/forged etc)
HTH
WopOnTour
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WopOnTour said:
EGGSactly right!
Hello, it was measured with a inside micrometer that was verified with an outside mic that was standard before use. Then i measured it in 4 spots to check the taper and out of round. A .0005 taper and not out of round. The other cyl. was .0005 larger. Standard bore in yamaha languge is 60mm. Thanks Rich.
WopOnTour
Member
OK cool.rich said:
Sounds like you've pretty accurately measured your bore andit's square enough (assuming your 4 measurements were centerline and 90degrees, top and bottom of the swept surface) Assuming 2.360 as the"new" bore dimension you're probably right at the very edge of thewear tolerance. (+0.002" typically on a cast bore)
English or metric doesn’t really matter obviously but usewhatever units your measurement tools are equipped with and only mathematicallyconvert when you have to. (often where errors are made)
So now measure your new pistons at/near 0.4" (10mm)from the bottom of the skirt and subtract this from your bore measurement todetermine the piston clearance.
I don’t have the actual specs for your old Enticer but Isuspect the stock cast piston clearance rebuild specification was ideally ~0.0015"-0.0018"(0.040-0.045mm) but I probably wouldn't exceed .0025" clearance unless itwas a race engine or an aftermarket forged piston (manufacturers like Wisecooften specify stock clearance + additional of 0.0005-0.001" or even moreto prevent "squeakers" and cold seizing). Now if your pistonclearances cannot be met, (and you want it to last) you should either find apair of +1 or +2 pistons (in a 12/24 box of pistons you will quite commonlyfind a number of them slightly larger and some slight smaller than standard upto a thousandths or two) else you're looking at boring or sleeving.
HTH
WOT
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Ok, yeh i measured centerline and 90 degrees. I redid the conversion for mm to inches and it came out 60 mm= 2.362- which is what it measured. I used 2 differnt conv.pages i googled and thats how i got the first reading of 2.360. Im waiting for the new pistons to get here and will measure them up as you said. Thanks for all the help, Rich.