Author Topic: CR 250 head gasket on the TRX250R (Read 8502 times)

4 fouse · « **on:** February 20, 2014, 03:57:00 AM »

By putting a CR 250 head gasket on the R. What does that actually do. I'm new to this and I've heard people talking about it. Trying to get a better understanding.

mennis1971 · « **Reply #1 on:** February 20, 2014, 07:52:22 AM »

It bumps up your compression since it's thinner. I usually ran 2 base gaskets when doing that mod. The 2 base gaskets slightly raise your ports and the thinner head gasket gives you more compression. Both are good cheap mods for a stock(no porting or headwork done) cylinder that give ya a little more HP. Hope that helps answer your question. BTW with both of those mods done, I was still able to run pump gas(non ethanol of course--ethanol gas is crap). It put my compression right around 180-185.

rablack21 · « **Reply #2 on:** February 20, 2014, 09:24:31 AM »

Mennis nailed your original question ^^^

I tried the cr250 head gasket trick once, but I never could get it to seal. It leaked coolant on me. Honestly, I'm not really sure that it is needed. My stock cylinder and head ran 185psi anyway. Unless your engine is starting to lose compression, I don't see the need. And if you are really wanting to bump up your compression, get your head shaved down or get a cool head with a race gas dome and then run race fuel. Of course, you don't really all the benefit out of this on a non ported cylinder. Just my own personal opinion, I don't think it is worth doing.

Jerry Hall · « **Reply #3 on:** February 20, 2014, 10:24:39 AM »

Quote from: 4 fouse;26202

By putting a CR 250 head gasket on the R. What does that actually do. I'm new to this and I've heard people talking about it. Trying to get a better understanding.

The single layer CR 250 metal head gasket will raise the compression and leak on about half of the engines we see them installed on. The gasket was designed to be used on the plated cylinders whose gasket is clamped between two surfaces made of the same metal. The TRX cylinders have an iron sleeve. A head gasket that is clamped between surfaces that has two different metals has to have more resilience than a gasket that is clamped between two surfaces made of one metal.

The iron sleeve needs to be .001" to .003" taller than the aluminum for the single layer steel CR250 gasket to work properly. The iron sleeve on most of the TRX 250 cylinders sets even to a few thou lower than the aluminum gasket surface.

Aluminum and iron expand at different rates. Aluminum typically expands almost twice as much as iron due to a temperature increase. If you start off with the head gasket surface flat at room temperature, the sleeve will drop below the aluminum surface when the engine is up to operating temperature. The clamping force between the head and the sleeve decreases as the temperature of the engine increases.

There are a lot of shade tree modifications like using the CR250 gasket but there is no free lunch on this application. The proper type of head gasket needs to be used on a cylinder with an iron sleeve and the head and deck need to be machined to get the proper piston to head clearance and combustion chamber shape.

Tbone07 · « **Reply #4 on:** February 20, 2014, 11:15:21 AM »

I did the CR250 gasket mod on my OEM cylinder and it ate/leaked coolant pretty bad. I think it would be better to go with an o-ring Cool Head setup and get a smaller dome to raise compression

I've always had good luck with o-ring heads

Rupp250 · « **Reply #5 on:** February 20, 2014, 04:00:26 PM »

Another option is to get the stock head re-cut. Not just shaved but an actual re-shaping of the bowl.

mennis1971 · « **Reply #6 on:** February 20, 2014, 07:36:21 PM »

BTW I did that cr gasket to both 85 and 86 cylinders(the same ones over and over) several times with no problems. Not trying to discredit anyone's own experience with this mod; I'm just sharing my experience. Most coolheads are non O ringed(about 90% I believe according to PD). My coolhead is non o ringed BTW. Mine leaked immediately(without even starting the engine) when using a cheap paper gasket with the metal ring in the center. Throw those in the trash IMO.

Obviously it's best to do things the right way(porting and head mods)-- but being a poor student at the time, that wasn't an option. Honestly I'd say to save your money and wait til you can afford that stuff, but it did work for me and I gained a little HP, but it was a gain.

Make sure your jetting is spot on. You could just as easily gain that same HP with just some jetting changes. Troy's stock 89 ran great with a stock carb(jetted great) and stock pipe with the cr headgasket. It ran good enough that it was hard to believe it was bone stock(or at least very very close).

Good luck if you choose to try this out. I did it and it worked, but I know that Jerry has worked on way more R's (not to mention other stuff) than me so I'd personally take his advice over mine as he is an expert and I'm not.

Wes350x · « **Reply #7 on:** February 20, 2014, 07:42:35 PM »

I've used previously and currently just one of the thinner parts of the Trx 3-piece OEM gasket and it's always worked fine for me to bump compression.

4 fouse · « **Reply #8 on:** February 20, 2014, 07:46:03 PM »

Thanks for the info guyd

C-Leigh Racing · « **Reply #9 on:** February 20, 2014, 07:50:57 PM »

Hummm, what is that stuff that we all should have as a standard item in our tool boxes ?.
Neil

Wes350x · « **Reply #10 on:** February 20, 2014, 07:56:37 PM »

Quote from: C-Leigh Racing;26304

Hummm, what is that stuff that we all should have as a standard item in our tool boxes ?.
Neil

Duct tape

Pumashine · « **Reply #11 on:** February 20, 2014, 08:33:22 PM »

When I ran the thinner gasket the piston got ate up using premium from the pump. Would not recommend unless you go to race gas.