viking9990 Posted November 11, 2007 Report Share Posted November 11, 2007 got cub cyl stock stroke big bore 68mm pistons everything brandnew . running 19cc domes did a compression test and i'm right at 140psi both sides. i'm thinking with this setup i should be right at 175 to 185 psi. maybe i should try 68.5mm piston rings for a tighter fit ? maybe loosing crank pressure? we rebuilt my frends bike stock cly's 66mm bore also with coolhead and 19cc domes 185psi and his bike gets up 1 2 3 4 gearing same on both bikes 15/39 my bike only 1 2 the only diffrence between the bikes is that i have a plus 2 inch swingarm would that make that big a diffrence. Quote Link to comment Share on other sites More sharing options...
inthemail Posted November 11, 2007 Report Share Posted November 11, 2007 got cub cyl stock stroke big bore 68mm pistons everything brandnew .running 19cc domes did a compression test and i'm right at 140psi both sides. Any need for a hone on your new cylinders? brand new shouldnt require a larger ring, even with a honejob. 140 dead on both sides makes me think that your top end is all good compression loss must be down low. Basegasket new too? Quote Link to comment Share on other sites More sharing options...
viking9990 Posted November 11, 2007 Author Report Share Posted November 11, 2007 Any need for a hone on your new cylinders? brand new shouldnt require a larger ring, even with a honejob. 140 dead on both sides makes me think that your top end is all good compression loss must be down low. Basegasket new too? yes base gasket new as well Quote Link to comment Share on other sites More sharing options...
Dave I. Posted November 11, 2007 Report Share Posted November 11, 2007 what is your elevation? Did you check your squish when you built it? About getting up or wheelies, you might be spinning the tires...these cubs have some major hit... Quote Link to comment Share on other sites More sharing options...
dajogejr Posted November 11, 2007 Report Share Posted November 11, 2007 I think you should measure a few things first... Measure ring end gap. Measure piston to wall clearance, and most importantly, measure squish. Quote Link to comment Share on other sites More sharing options...
bansheeseat$$ Posted November 11, 2007 Report Share Posted November 11, 2007 Also make sure you didn't get a +4 stroke cylinder configuration instead of the stock stroke cylinder setup... Quote Link to comment Share on other sites More sharing options...
dajogejr Posted November 11, 2007 Report Share Posted November 11, 2007 Also make sure you didn't get a +4 stroke cylinder configuration instead of the stock stroke cylinder setup... That, my friend...is exactly why I asked him to measure squish... That "+2mm" of squish would be a tell tale sign... Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted November 13, 2007 Report Share Posted November 13, 2007 Any need for a hone on your new cylinders? brand new shouldnt require a larger ring, even with a honejob. 140 dead on both sides makes me think that your top end is all good compression loss must be down low. Basegasket new too? DO NOT hone your cubs. They are plated, honing them would ruin the plating (costs @ $200 for replating) I'm currious how the cubs porting may affect the compression compared to a set of stock cylinders???? Quote Link to comment Share on other sites More sharing options...
Stellar Performance Posted November 13, 2007 Report Share Posted November 13, 2007 (edited) DO NOT hone your cubs. They are plated, honing them would ruin the plating (costs @ $200 for replating) I'm currious how the cubs porting may affect the compression compared to a set of stock cylinders???? I was in the same boat. My 7mil cub 68mm bore with 20cc domes only pulled about 155 psi or so. My stock cylinder 65.50mm bore stock stroke with 19cc domes pulled 178. The stockers were drag ported too. As far as having a 4mil cylinder.....you wouldn't have crap for compression. You would have to kick over your bike so fast to even come close to 140 psi, your leg would fall off.....LOL Anyone else with cubs noticing the lower static compression numbers? Edited November 13, 2007 by AZCUSTOMQUADS Quote Link to comment Share on other sites More sharing options...
FireHead Posted November 13, 2007 Report Share Posted November 13, 2007 Anyone else with cubs noticing the lower static compression numbers? It all depends on what sort of porting you have and who did it. My engine in my red bike has about 140psi with 21cc domes, but I fiddled with the porting and the domes. :biggrin: Quote Link to comment Share on other sites More sharing options...
Animalman294 Posted November 14, 2007 Report Share Posted November 14, 2007 My 4 mil is around 185-187, but I just had a clean up of the castings so nothing major............. Quote Link to comment Share on other sites More sharing options...
Dave I. Posted November 14, 2007 Report Share Posted November 14, 2007 68x54, 19 cc domes, 185 psi Quote Link to comment Share on other sites More sharing options...
FireHead Posted November 14, 2007 Report Share Posted November 14, 2007 68x54, 19 cc domes, 185 psi That sounds about right. :thumbsup: Quote Link to comment Share on other sites More sharing options...
duneloon Posted November 14, 2007 Report Share Posted November 14, 2007 Check the squish. I bet its around 60 thousanths. What is the deck hight? Quote Link to comment Share on other sites More sharing options...
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