what are the symptoms of having a cylinder out of round?

just ran a comp test on my 11.8.1 b20 vtec and pulled over 250psi per cylinder bar number 1 which was 225. the gauge only ran up to 250psi and it should make around 260 psi with that piston/head combo.

put oil in the bore and tried it again and bam right up to the same as the rest.
i checked the ring end gaps at several points in the bore and they were fine, also piston to wall were fine and all within honda specs.

pcv crankcase is quite smokey, it always has been (running 3 valve cover ports and 1 block, venting to atmosphere). car uses no more oil than any other vtec motor i have owned and uses no coolant.

ideas?

 

Wow, thats a **** load of compression

Did you orient the pistons rings correctly on the piston prior to install? In most cases putting oil in the cylinder and it coming up to pressure is a ring sealing issue. Did you measure the bore before the build? Was it honed/bored before the build? Or was this a stock motor that just freshened up with a ball hone?
If you checked the piston to wall clearence, were the readings the same all around the cylinder or did you only check 1 or 2 spots?

 

Do a leakdown test.
We had a B20Vtec with a similar issue. Turned out that one cylinder had over 30% leakdown. Ended up being the rings were almost aligned with each other. Re-ringed it with a quick flexhone and now it reads less than 3%.

 

thanks for the info :D

i am 99.9% sure the rings are all gapped right. i followed the info i got from www.theoldone.com (if you look at the ring gapping the top two rings are 180 apart from each other as are the oil rings, making it pretty difficult to get them out of spec)
the bores were in pretty good nick. i only broke the glazing with a hone (tripod spring loaded one) and tried to get the cross hatch as per the above article (60 degree cross hatch)

ring gaps were all within tolorance as per the b20 manual (all reading between the mid gap, so not to tight, one or two were a little loose, but only very slighty)

set and checked all the way down the bore (i dont have a bore gauge to check for roundness) so i used the top "fire" ring and checked the clearance every inch down the bore. all looked ok.

how big a scratch would there need to be in the bore for me to loose 25-35 psi of compression from it? would a very very fine one do it?

i have a leakdown tester on order, so i will see what the leakdown numbers/percentage is once i get it on.

i managed to bag a b18c4 long block and crank today (like your gsr but already a vtec block, so no oil lines to run etc etc) for cheap so i am pretty tempted to go turbo and keep the b20 as a long term nasp project once i can get it apart.

thanks, it made good numbers bar the last cylinder, not bad for an 11.8.1 b20, jsut glad we get 98 ron fuel at most stations :D
i do have some pics of my cylinders when i took it apart, there was a very very fine score in the bore then, but it was so fine my fingernail would not catch it

 

leak down tester should turn up today or tommorow so on sat i shall nip over to the garage and give it a whirl.

what sort of figures should i be getting on a healthy engine? 5-10% ?

also how do you define where its being lost? just listen to the exhaust/intake pipes and watch the coolant for bubbles?

cheers

 

According to SAE 30% is an ok number.
For high performance Honda engine I hear it has to be less than 2%.
You got it right as far as telling where the air is going.
Good Luck!

 

i am so hoping its going out via my head or via a gasket and not the cylinder. but with oil in the bore and the compression shooting back up i bet its a ring issue (unless the oil coats everything in the cylinder like valves etc?)

sucks as i only put it together 2000 miles ago after other issues.
got offered a b18c4 vtec block for cheap so i have that as a spare and going to collect a b16 complete engine for some work this weekend.

not sure if it is by the rings what i should do.
either my block is cracked, or my cylinder is scored or the cylinder is not straight in relation to the others/out of round. i am either going to have to bin the block, or overbore the block 0.5mm and buy 84.5mm pistons. (but i am reluctant to do this as its taking more materiel from an already thin wall)
if its veggied i think using the b18c4, forging it and running a low blow turbo setup is going to be the best bet.

how hard is it to use a bore gauge to check for roundness? also can you get them for good money (less than $200? ) all the ones i see are mega money
.

would just be nice if it was a valve or a gasket....so so much cheaper

 

piston ring clocking:
http://theoldone.com/articles/engine...istonfacts.htm

 

thanks but thats how i already gapped and measured them