spacer plate??

[87250rxrider]

i'm finally wrapping up my 250r project build, and i am having a question with the engine. right now, the engine is an 89 bottom end... i have a cylinder mx ported by Neil at NPRD, also known as cleigh racing. right now the engine has a 2mm spacer plate in it, but the piston still travels up into the 3-layer head gasket... the big problem is that the owner before me had a problem with it blowing the head gasket b/c of the compression. it has a pro design cool head and with the 19cc race dome it has a compression reading of 230+ PSI. with the 21cc dome i'm expecting it to still be over 210PSI?? the piston also sits higher than the bottom of the intake ports with the 2mm spacer plate. i'm wondering if a 4.5mm spacer plate from duncan motorsports would be a good idea to keep the reliability up in the engine?? the piston sits probably over 2.5mm higher than the bottom of the intake ports at BDC and probably around 1- 1.5mm into the topend gasket(how thick is a 3-layer gasket??...if i know how thick one is i can give you a better estimate). i'm guessing with the 4.5mm spacer plate the engine would drop compression to the PSI that it should be around, and also raise the reliability and the life of the head gasket(blowing head gaskets was a problem before i bought the engine. BTW, the cylinder is at a 69mm bore and was just honed. the guy i bought it from said it was a 4mm stroker but wasn't exactly sure...does anybody know if this is a 4mm stroker by the readings given?? if anybody can answer any of my questions, that would be greatly appreciated.
sorry for the long post.
thanks,
-Ryan

[deathman53]

is this motor using a yz piston??? if you use one, you need a different sized spacer plate, also, did you get the correct head gasket for a 69mm bore? I'm told you have to use the head gasket for the 295 big bores on the 69mm and up bores.

[87250rxrider]

this motor is not using a YZ piston, just an 86 wiseco piston. i'm not using a special gasket, but one that has been cut to allow the piston to go up into the gasket. this should not change my problem. either way, the compression would be too high, neither gasket will help with that. anybody else have any suggestions?

[machwon]

Typically the spacer you are using is for use with a YZ piston. The thicker spacers go with the 86 wiseco pistons.

[350rpowervalve]

Try this is not dangerous because I have a 15mm on my r...

[brokeitin3]

definitely get a digfferent spacer, the 4.5mm would be the correct size. i got the same setup as you. only with an 88 cylinder. i got the 18cc dome, 86 piston .20 over. my compression is at about 195 psi. thats right where i like it.

[wilkin250r]

Did you get your porting done by Neil yourself, or did you buy it already ported.

Basically, what I'm asking is: Do you already have some sort of personal interaction with Neil?

If so, I highly suggest you talk with Neil about it, he's very knowledgable on the subject.

Aside from that, I can only offer basic advise. Building a stroker motor is not easy, it requires a lot of knowledge. The increased stroke alters all your port timing, which changes your pipe needs, ect. The more I learn about port timing, I would never tackle the job of trying to build a stroker motor myself. Some people would say I'm a smart guy, but I'm still far short of the level of knowledge needed to build a proper stroker. You really need an expert.

Neil himself talks about this very problem over at MacDizzy. His exact words:

"Another mistake made alot of times building a stroker engine, is trying to use a cylinder thats already been ported for a stock stroke. Its hard to make the owner understand, that the cylinder they have been running cant be used, just cant see why or for the extra cost of replaceing the cylinder."

[87250rxrider]

hey guys... thanks for the info, but this post is a little old. i already got and installed the spacer plate, and it perfectly aligns all the ports, and puts out around 190PSI. i'd say i'm pretty pleased with the results of the thicker plate. BTW, wilkin, i have talked to Neil many times.
thanks,
-Ryan

[2muchquad]

"Another mistake made alot of times building a stroker engine, is trying to use a cylinder thats already been ported for a stock stroke"


Dah..thats why there are spacer plates...hello:D

[deathman53]

no, in most cases the spacer plate is used for the correct deck height. IE: 85/86 piston on 87-89 rod, without the spacer plate the piston will ~5mm over the deck height, same goes with the yz piston, this will be about 3mm over. Yes, some strokers use spacer plates as to correct the deck height, NOT the port timing. If you are using a 85/86 piston and 87-89 rod on a stroker crank, regardless you will need to spacer plate to correct the deck height. Also different size strokers require them to correct the deck height for the specific one you are using.