50mm bbk KABOOM!

bakaracer · Post by **bakaracer** » Tue Jul 26, 2011 9:42 pm

when you say the piston is above the deck, is the the top of the piston or the edge of the piston? if its the edge of the piston and your only getting 120psi of compression. then something is seriously wrong.either your gauge is leaking or you have major blow by going on. with a .6mm of squish and 50mm bore and mini stroke crank, compression reading should be in the 160psi++ range. check your ring end gap clearance and piston to cylinder wall clearance.ring end gap shouldn't be more than .017

guen84 · Post by **guen84** » Tue Jul 26, 2011 9:52 pm

bakaracer wrote:when you say the piston is above the deck, is the the top of the piston or the edge of the piston? if its the edge of the piston and your only getting 120psi of compression. then something is seriously wrong.either your gauge is leaking or you have major blow by going on. with a .6mm of squish and 50mm bore and mini stroke crank, compression reading should be in the 160psi++ range. check your ring end gap clearance and piston to cylinder wall clearance.ring end gap shouldn't be more than .017

i mean the edge of the piston, i did buy a new compression gauge to try. i will check the ring end gap, but what is the piston to cylinder wall??

bakaracer · Post by **bakaracer** » Tue Jul 26, 2011 10:07 pm

clearance between the piston and the cylinder wall. should be no more than .015. check to make sure the oring for the compression gauge is there on the end. make sure its tight when you screw it in the spark plug hole. hand tight then use a plier to turn it another 1/2 turn.

guen84 · Post by **guen84** » Tue Jul 26, 2011 11:32 pm

ok heres the verdict, ring clearance is .012 and cylinder wall clearance is less than .011 smallest feeler gauge i got.. turns out it was the compression gauge!! hit 170 with the new gauge.. well the difference between the old and the new put my last cylinder in the 190 ball park, guess we know why that blew up... should i add a base gasket??? only concern with that is intake duration, is at 132 now, adding another base gasket will make it even longer, exhaust is at 182 now so that should still be ok... thanks for the help..

bakaracer · Post by **bakaracer** » Tue Jul 26, 2011 11:48 pm

add another head gasket. dont worry, i ran 4 head gaskets before with no issues.thats why I dont like the 44.1mm mini stroke crank. the 43.2 one gets it a little closer. you can call vt cycles and ask to see if they have anymore thick copper head gaskets. steve has them in different thicknesses and sizes.

JJ Joseph · Post by **JJ Joseph** » Wed Jul 27, 2011 12:23 am

guen84 wrote:possibly try one of limp's 51mm ruima kits now.. any one have some feed back on them over a Molossi kit..

I have over 6,000 mils on a Ruima 50mm BBK, using the stock boost port, #90jet, stock needle, V8 28mm exhaust. It starts fine every morning, runs fine on the highway at 50mph. The Ruima head doesn't match the Honda plastic cooling shroud (the spark plug is in a different location), so some fiberglas surgery is required.