kbone77 Posted January 26, 2009 Report Share Posted January 26, 2009 I installed a 4mm stroker 5mm longrod crank on my 2000. my compression is low at 125psi both sides. it's a fresh topend 65.5mm pistons, w/ a noss coolhead w/ 20cc domes. I was expecting the compression to be higher. I used a base spacer and I'm thinking that could be the source of my low compression, or the cause of poor performance. The exhauxst port is stock, and is approx 29mm from top of the deck. My main question is: Does using the base spacer w/ stroker crank mess up your port timing, and potentially the performance? seems like it would. I used it simply because it came w/ the kit-and I didn't know any better. Should I scrap that spacer and get some domes for the coolhead to accomodate the additional 2mm upstroke? Anyone know the piston/head clearance at TDC? Quote Link to comment Share on other sites More sharing options...
2001Stroker Posted January 26, 2009 Report Share Posted January 26, 2009 Did you get the cylinders ported for the 4mil, longrod? Personally, I would ditch the plate and get stroker domes. Quote Link to comment Share on other sites More sharing options...
kbone77 Posted January 26, 2009 Author Report Share Posted January 26, 2009 I sent the jugs out to LA Sleeve and they said the existing port was fine. they just cleaned things up and did a bore and matched the pistons. what type of porting is done to match a stroker? Quote Link to comment Share on other sites More sharing options...
locogato11283 Posted January 26, 2009 Report Share Posted January 26, 2009 do you have stroker domes instead of regular domes? if so than thats the problem. most GOOD 4mm setups dont use the spacer plate. in your case since you used your cylinders with existing porting and a spacer plate, you should NOT be using stroker domes. you need regular domes. i bet thats your problem. if you decide to ditch the spacer plate, you will have to have your cylinders reported or buy new ones. then you will need to use stroker domes, which is the preferred method by most everyone. Quote Link to comment Share on other sites More sharing options...
kbone77 Posted January 26, 2009 Author Report Share Posted January 26, 2009 I got the domes used on ebay, they were not listed as stroker domes. maybe they actually are though, I'll have to remove the spacer and check clearances. still confused on the porting-without the spacer the port timing would be exactly the same as w/ the stock crank-wouldn't it? with the spacer plate -the degrees would be different then stock, because the spacer effectively moves all the ports up 2mm. or are you simply saying additional porting for flow is required for the additional displacement the stroker creates? Quote Link to comment Share on other sites More sharing options...
Bancheez Posted January 26, 2009 Report Share Posted January 26, 2009 or are you simply saying additional porting for flow is required for the additional displacement the stroker creates? No, if you are running stock port cylinders, you HAVE to run a spacer plate. If you want to run stroker domes instead, you would have to have the cylinders ported to affectively "raise" the ports for the 4mm stroke, and ditch the plate. one or the other... except, I have run stock port cylinders w/a 4 mil crank, (no "plate"), and stroker domes in the past. makes a excellent woods bike, TONS of low-end, but NO top-end...and if you try to run them on top, set-up like this, the motor won't last too long. Quote Link to comment Share on other sites More sharing options...
blowit Posted January 26, 2009 Report Share Posted January 26, 2009 I got the domes used on ebay, they were not listed as stroker domes. maybe they actually are though, I'll have to remove the spacer and check clearances. still confused on the porting-without the spacer the port timing would be exactly the same as w/ the stock crank-wouldn't it? with the spacer plate -the degrees would be different then stock, because the spacer effectively moves all the ports up 2mm. or are you simply saying additional porting for flow is required for the additional displacement the stroker creates? No, timing between a stock crank and 4mm crank are totally different when comparing on the same cylinders. The key word here is rod angle. Porting for a 4mm addresses not only timing issues but changes in cylinder flow from the stroker crank. At least when it is done correctly... Yes, you need to lose the plate. I strongly suggest you get an engine builder to look at your engine. Brandon Quote Link to comment Share on other sites More sharing options...
blowit Posted January 26, 2009 Report Share Posted January 26, 2009 (edited) No, if you are running stock port cylinders, you HAVE to run a spacer plate. If you want to run stroker domes instead, you would have to have the cylinders ported to affectively "raise" the ports for the 4mm stroke, and ditch the plate. one or the other... except, I have run stock port cylinders w/a 4 mil crank, (no "plate"), and stroker domes in the past. makes a excellent woods bike, TONS of low-end, but NO top-end...and if you try to run them on top, set-up like this, the motor won't last too long. huh ?? Edited January 26, 2009 by blowit Quote Link to comment Share on other sites More sharing options...
kbone77 Posted January 26, 2009 Author Report Share Posted January 26, 2009 It is a ported motor-I was simply stating that the exhaust port height was stock. sorry if I failed to mention that. The exhaust ports have just been cleaned up, and the intake/transfers have been ported out. I think they used to call this a stage 1. Prior to the stroker crank build it worked very well w/ the CPI inframes at the dunes. had a nice mid range punch w/ never ending topend. After the stroker build it didn't run as good as before, I believe due to the low compression. Just trying to gather as much info as possible and resolve the compression issue- before I put it back together. Quote Link to comment Share on other sites More sharing options...
kbone77 Posted January 26, 2009 Author Report Share Posted January 26, 2009 Thanks Blowit. Ditching the plate sounds like the right way. Then I'll need to confirm which domes I have, they were supposed to be regular, but may actually be stroker domes.-But that would obviously explain the compression problem. Trying to do everyhthing myself that I can-I'm hesitant to take it to a shop because of bad/expensive past experiences. Quote Link to comment Share on other sites More sharing options...
locogato11283 Posted January 26, 2009 Report Share Posted January 26, 2009 huh ?? hahaha i was about to quote his post and say the same thing.. i agree about getting rid of the spacer plate. that is a ghetto way to do the 4mm motor. do it right and have your cylinders ported correctly and run stroker domes. Quote Link to comment Share on other sites More sharing options...
bansheefreak Posted January 26, 2009 Report Share Posted January 26, 2009 before you tear it apart do a sqiush test... this will tell you alot... if you need help just pm me... Quote Link to comment Share on other sites More sharing options...
Bancheez Posted January 26, 2009 Report Share Posted January 26, 2009 whats the question?... Quote Link to comment Share on other sites More sharing options...
bansheefreak Posted January 28, 2009 Report Share Posted January 28, 2009 did you do a sqiush test yet??? Quote Link to comment Share on other sites More sharing options...
Wildcardracing Posted January 28, 2009 Report Share Posted January 28, 2009 If he were running stroker domes and a plate the compression would be much lower than 130. I suspect either a faulty guage, not holding the throttle wide open during the test or not kicking it enough times. Were the cylinders within 5psi of each other? The motor had allready been ported before the 4mil, I suspect his running issues are because with the plate the transfer port durations are too high. This will cause the bike to not rev out as far as it should Quote Link to comment Share on other sites More sharing options...
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