What compression ratios can use pump V/race

[Jerry Hall]

I was reading an older post in the engine section about the CR head gasket and some people were saying that it has a problem leaking coolant. I think I am one of those people. When I bought my R the guy I bought it from said he had just done a top end on it and used a CR head gasket boasting about compression boost. After my first ride I noticed a leak and retourqued and it still leaks.

I just ordered a top end gasket set and I plan to do a flat sand on the head to tune up the surface (figure 8 motion, 400 grit paper on a piece of glass) but if I was dropping on a cool head no flat sand and I would not be throwing away a head gasket in a month.

I have also realized I can't get where I want to go with out race gas

The .010" thick CR 250 head gasket was really made for cylinders with plated bores (cylinders without a sleeve). When your cylinder (the aluminum casting) comes up to normal operating temperature it expands and the length increases about .004 to .006".  The iron sleeve also expands and the length increases .002" to .003".  This means that at room temperature the top of the cylinder can be perfectly flat but when the cylinder is up to operating temperature the iron sleeve may drop a little.

The sleeve moves in all cylinders as the temperature changes, but some move more at the top and some move more at the bottom of the cylinder.  This is why some guys use the thin gasket and do not have problems and others have nothing but problems.  

It is really best to use a gasket that was made for your type of cylinder and then do the appropriate machine work to the top of the cylinder and head to get the piston to head clearance and the combustion chamber shape correct.

[Pumashine]

I was reading an older post in the engine section about the CR head gasket and some people were saying that it has a problem leaking coolant. I think I am one of those people. When I bought my R the guy I bought it from said he had just done a top end on it and used a CR head gasket boasting about compression boost. After my first ride I noticed a leak and retourqued and it still leaks.

I just ordered a top end gasket set and I plan to do a flat sand on the head to tune up the surface (figure 8 motion, 400 grit paper on a piece of glass) but if I was dropping on a cool head no flat sand and I would not be throwing away a head gasket in a month.

I have also realized I can't get where I want to go with out race gas

After flattening the head you can use the stock 250r gasket to put you back at pump gas. Seems like guys do the thin head gasket thing to sell the bike. The guy I bought from even lied to me and said it was a 310. I don't think the extra head aches with using the thin head gasket are worth the benefits. Race gas is spendy. Get your cylinder ported and stick with pump gas.

[wilkin250r]

I'm going to agree with Puma.  Race gas is obviously better, but I think you can still get decent power from pump gas.  If I was given a choice between a properly, quality ported cylinder on pump gas or a stock cylinder with race gas, I would definitely choose the ported cylinder.

There is obviously going to be a cost issue.  Porting will cost you up front, while race gas will cost you down the road (forever).

One of the risks with getting your cylinder ported, however, you definitely need to know your riding style and the type of power delivery you're looking for.  If you're a trail rider, but you demand your engine builder give you max power, you're gonna end up with a drag port job and you'll be hating life.  Thankfully, most reputable engine builders will spend a few minutes with you and ask you questions to determine your exact needs, and that's a good time to also discuss your options for getting your stock head rechambered, or an aftermarket head, and get it all done as a package deal.

[c_williamson007]

Hmmm... Well I guess the moral of the story here is there is not just one secret to getting good dependable power its a combo of so many things it can't be told in a post it must be learned over time and when you pay an engine builder to build you that power you are paying for his years of r&d.

Thank you all for your input. The knowledge and resources of this forum and its members are fantastic.

[wilkin250r]

Exactly.

Like the old addage "nothing is free".  People think you can save money by doing things yourself, but it takes huge amounts of time and research to learn to do those things properly.  So you have a choice, to pay in dollars by sending to an engine builder, or pay in time (and still some dollars) learning to do it yourself.

As the years pass, I think the engine builder is actually the cheaper of the two options, and usually better results.  But it's not nearly as fun.

[udontknowme]

trying to do 1 or 2 engines for yourself isnt even worth it. good porting tool setup is about a G but can get even more expensive than that. and without knowledge the tools are useless.

[broken1]

trying to do 1 or 2 engines for yourself isnt even worth it. good porting tool setup is about a G but can get even more expensive than that. and without knowledge the tools are useless.

I ported my own cylinder with a micro die grinder that cost me $60 & an old dremel. I'm by no means a professional engine builder but my R ain't no slouch & I been running it hard for over 25 years. Anything can be done if you have the knowledge & will.

[c_williamson007]

I ported my own cylinder with a micro die grinder that cost me $60 & an old dremel. I'm by no means a professional engine builder but my R ain't no slouch & I been running it hard for over 25 years. Anything can be done if you have the knowledge & will.

I know enough about 2 stroke port timing to be dangerous but not enough to make good dependable power. I ported a pocket bike engine once just to see what would happen and I raised the exhaust port too high and it would make massive high RPM power but the lack of low end made it useless and eventually blew apart because the Chinese parts were not ready for the RPM.

I respect the man who will take the time to get the knowledge but the price of a new cast cylinder with porting, revised cooling and a o-ring head with adjustable domes is $750.
If I work in my trade it's about $50 per hour so for 15 hours of work I got dependable power. I know I can't learn it, get the tools and do it in 15 hours.

Big ups to you for what you have done. I'm sure it makes you feel that much better when you put it down on other riders with all their fancy store bought stuff and you are riding a bike that you hand built.

[Jerry Hall]

Exactly.

Like the old addage "nothing is free".  People think you can save money by doing things yourself, but it takes huge amounts of time and research to learn to do those things properly.  So you have a choice, to pay in dollars by sending to an engine builder, or pay in time (and still some dollars) learning to do it yourself.

As the years pass, I think the engine builder is actually the cheaper of the two options, and usually better results.  But it's not nearly as fun.

Yes, yes, yes!!!!!!!!!!!!!

I.........we engine builders have already made most of the mistakes turning mountains of heads ,cylinders and other engine components into junk looking for the engine combinations that make power and do it with acceptable reliability.  I think most people will find our experience is going to be a lot cheaper than the customer trying to reinvent the wheel.

[udontknowme]

im sure anybody and everybody in this business started off with a die grinder, dremel, small hand files, and any other grinding tools they could get their hands on. first tool i had was a black&decker dremel with flex shaft attachment. at some point, usually rather quickly, you realize you need much better tools if you plan to stay in the business and have it be enjoyable. if i was forced to keep using dremels and air powered die grinders i would of thrown in the towel a long time ago