Compression

[Racerx63]

Anybody know how much compression would be gained by using the 89 CR250 head gasket instead of the stock 1986 one? Trying to get to about 210-215 compression.

Or how much to mill the head to get there?

Thanks

[zedicus00]

what compression do u hav right now. the cr head gasket and mill the head about 2 to 3 thousandths that is about the most u wanna do though or yur squish clearance will b all outta whack. that would get u around 190 sumwhere i would guess if yur piston an bore is good. u will need to send it sumwhere an get the head recut if u go much more. if u was going to go to all that trouble i would hafta suggest getting a coolhead and a race gas dome.

[Racerx63]

The compression before I pulled it apart was 180 cold. But this is the first time the top end has been apart ever. It had the stock original 66mm piston in it. It is so worn out I will probably have to go .50 on the bore to get it right again and figured I would do the head while it was apart. The port job I will have done in the summer. Probably what I should do is just put in the 89 cr gasket and leave it until I have it ported.

Thanks

[zedicus00]

yup, but if yur compression was 180 then that topend was not anywhere near worn out. ive seen fresh rebuilds that make 180. my 250r with a coolhead and cr gasket makes 185 (which is about 200 in the powerband becuz of the way its ported and piped.)

[Racerx63]

Interesting, you would think after 18 years the piston would be worn out. The bike is cherry but my cousin that had it before me rode it quite a bit. There has to be with no exageration 150-200 hours on this piston. That is a heck of a testiment to the original Honda parts.

Thanks for the info.

[zedicus00]

depends on how it was ridden an maintained. if i remember right though average stock compression is around 170. hell ive seen em runnin still as low as 120. right after that the skirt shattered though. also sum peeple will replace jus the piston and rings withought boring it out if the bore is still anywhere close to within spec and that helps a lot. it may hav had 2 pistons since new and jus always been replaced with fresh stockers.

[Racerx63]

That is true. It was not ridden very hard. He owned it since 1989 and said he never had any motor work done to it other than change the plug and tranny oil. MAybe this bike is cherrier than I thought. I'll have to take a bore gauge to it. It is possible it does not need anything but rings and a hone. The last two trips I have noticed that the power was dropping on it. The bottom end power was almost non existent.

Thanks,

Mike

[zedicus00]

check and regap the plug. and check the stator and coil. 250rs hav notorious coil issues. but if it had 180 compression there is no reason to pull the topend apart unless yur modding sumthing. also check, clean and or replace the air filter and the carb. anyone of thouse could kill the bottom end. does it still hav the stock pip on it? if its full of carbon clogged and or the packing is shot then it needs cleened an replaced too.

[Racerx63]

I have put a FMF SST pipe on it and have already repacked the silencer. I clean the air filter every trip it is a K&N. The carb I have not gone through yet. I will measure the bore tonight to see how worn it is. How would you check the stator and coil? Is there certain volt level it should show on a meter?

Thanks,

Mike

[zedicus00]

the coil can be OHMed i dont remember right off hand what it should b thoguh, i will c if i can look it up for u. the stator u can jus take to anywhere that does motor winding an they can check test an rewind it. also the wire harnesses tend to get briddle and add resistance as time goes on, and its not unheard of for the cdi to give up. basically there is a ton of little things that it could also b or that could b adding to the problem. even on the best kept quad u hafta remember 18 yrs is quite a while for a performance machine.

[Racerx63]

No doubt 18 yrs old but one of the best. I do have a honda shop manual for it. I would think they would have values to be checked.

Thanks for the info.

[zedicus00]

coil should be very close to .3 on the primary and 10.5 on secondary. yup thas what the forums are for is helping. good luck with it.

[Racerx63]

Thanks again, I will test it tonight.

[JTRtrx250r]

Originally posted by Racerx63
There has to be with no exageration 150-200 hours on this piston. That is a heck of a testiment to the original Honda parts.

Thanks for the info. LOL...thats NOT too uncommon,

if your hard on the motor or race it, it has to be rebuilt more often, but Ive seen topends w/ 3 times that, they were definitly tired but were still running fairly strong, alot depends also on who assembled it and how its been maintained IMO.

I picked up an 85 atc-R motor and the guy said its a strong runner but hasnt ever had anything replaced, the rest of the trike was pretty hammered so I thought I better go thru the motor, turns out its still the stock topend , he said they rode at least 2 weekends a month for 8-10 yrs, not sure if I beleive that or not...but I was suprised to see the stock piston in it, guess some ppl definitly go by "if it aint broke---dont fix it"

:D

Good luck w/ yours x63

[Racerx63]

That is amazing. My cousin did take care of it. The frame is immaculate hardly any paint is scratched or missing. I went to the desert with him. It was only used in the dunes so I do know it was ridden a lot. Just easy miles I guess.

This will be a fun project. I just sold about a year ago my 1985 ATC 250R that I raced back in '85 and '86. I was hard to get rid of her. It had an '84 CR250 jug on it. It was strong. So much new technology out now it is hard to decide which way to go for the upgrades.


When you replaced the top end on the engine how far did you have to go on the bore. one size over or did you have to go further?

[JTRtrx250r]

a compression gauge is your pal:D I check mine pretty often..it'll let you know when it needs to be done

It only has to go past the next bore if its in bad shape, to me...I'd rather get more bores out of the cyl for a longer cyl life, the slight bit of power just isnt worth it to me to go past , unless its necessary

[Racerx63]

It had 180 psi when I pulled it apart. The cylinder walls and piston look worn but it was sealing pretty good. I am the same way. I am not racing or hill racing so getting the most possible HP is not a big deal. I am just hoping it is not so worn out that I can't just go to the .25 and have to go .50. What do you think about
Wiesco (sp?) vs Honda pistons?

[zedicus00]

we always go even over. like .20 .40 .60 pistons r readily available in thouse sizes. plus next piston u put in it hav it cermacoated on the top and dry lube coated on the sides it will last a lot longer, plus hav a piston timing port window put in the piston, and atleast hav the jug match ported. and run the cr head gasket. u will b amazed..

wiesco piston are fine.

[JTRtrx250r]

I run Wiseco, most important thing w/ them is letting it warm up good IMO, I dont even put mine in gear till I feel heat on the radiator etc, if you don give it a chance to warm..they're prone to 4 corner seizures, come to think of it...I dont think Ive ever ran many stock Honda pistons:D

some of the other guys can help better than I can w/ other pistons

[JTRtrx250r]

Originally posted by zedicus00
we always go even over. like .20 .40 .60 pistons r readily available in thouse sizes. plus next piston u put in it hav it cermacoated on the top and dry lube coated on the sides it will last a lot longer, plus hav a piston timing port window put in the piston, and atleast hav the jug match ported. and run the cr head gasket. u will b amazed..

wiesco piston are fine. Good point Zed,

I do the same w/ mine

[Racerx63]

Thanks for the suggestions. one question though what do you mean by match ported? Is that matching the port on the piston to the jug or just making sure all the ports line up to the sleeve in the jug? If it is just matching the ports in the sleeve I can probably do that myself without screwing anything up.

Thanks again

[zedicus00]

yup match the sleeve ports to the cylender ports. ive seen them 1/8 to a 1/16 twisted so jus matching them up makes a difference. also a new reed set up and bigger carb wouldnt hurt while yur in that area anyways. o dremel with the bore stile bit then go over it with a stone bit. lip all the ports that the piston and rings cross too. as i think of more tips i will post em.

[Racerx63]

Cool, that is what I was hoping you would say.

thanks, time for me to get busy.

[zedicus00]

i could post a lot of stuff about simple mods that dont cost mutch add a bit of performance an keep it stock lookin. a good one is remove the aribox snorkls an run with the box lid off. put the cap from a small spray paint can in the snorkle hole in the airbox fits perfect. if u use a k&n make sur eu do not colapse the plastic airbox ring, get a billet insert. new style cdi box from 88-89, i dont remember wat year u said yurs was. new reed is a big help. grab a v-force 3 for an 89 cr 250 but make sure u match port it to the trx boot. also yur pipe is a big perfrmance factor. get one like the esr trx - 5 since u dont really hav any porting dun.

[Racerx63]

Thanks, I do have the lid off and the pipe is an FMF SST. I was thinking of just replacing the reeds and keep the stock cage but maybe I will go ahead and just get the whole thing. Do their cages make a big difference over the stock cage?

[zedicus00]

yeah they help a lot although vforce is more of a hi rev reed setup. boysen or one of the others is better for midrange since u wont really hav any porting work done yet

[Racerx63]

Cool, mid range is what I am after. So the Boysen Rad valve is would be the way to go for me? You mentioned before to get it for the '89 CR250 though and port match it to the boot? That is better than getting just the TRX one?

[zedicus00]

only get it for the 89 cr if u r gunna use a vforce 3 valve. boysen jus get it for the 250r. make sure yur setup matches all the way through the engine. like if u get a mid range port job get a mid range pipe and reed to match and run the right compression for that setup... one thing out of whack on a 250r will make it a terd

[Racerx63]

Excellent, I really appreciate the advice.

Thanks

[Racerx63]

Well I tested the coil and the ohm load on the Primary was .5 (outside the limit) and I got a reading of 9.4 on the secondary.

Thanks

[86250rrider]

compression on mine was 165- with 3-piece trx gasket.dropped to 160,rebuilt it with double base gasket ? and cr250 head gasket .it was at 185 psi after rebuild.175 now. open box does help,so does v-force, very snappy response. i would definately use foam w/outerwear:macho

[papatrx]

Just curious, what was your reasoning for using a double base gasket?

[Racerx63]

86250rrider,

Thanks for the reply.

I am curious also. That would change the port timing. Not by much but it would.

[papatrx]

It seems as if any compression gained by going to the cr head gasket would now be lost by doubling the base gasket thereby moving the cylinder higher up at TDC. Mainly, you now run the risk of the intake venting at BDC if your piston is now below the floor of your transfer ports which is something not usually desired. I know of some tuners that will do this to help adjust for very radical port timing in stroked motors. I am not knocking what you did, just trying to understand what you were trying to accomplish.

[86250rrider]

to be honest with you ,it was like that when i got it from original owner.dont know why he did that but he said it ran better that way. those compression numbers listed above were ALL with the double base gasket so it did jump up about 15 psi with it for $15 instead of $30 for the trx gasket. well will raising compression help the bottom end pull for me and what is the comp# im going to want? you seem knowledgeable on 2 strokes help a newbie out. :D THANKS

[zedicus00]

i too hav heard of peeple run 2 base gaskets but its only been on engines with milled heads thin head gaskets and decked jugs. i couldnt justify running double gaskets on a non decked jug. then again ive never been in favor on decking a 250r jug iether.

[86250rrider]

if i used only one base i would pick up a few more psi with that alone. correct ?:confused:

[papatrx]

Since you really don't know the history of the cylinder, you should probably check your squish before you change anything, they might have doubled them up to account for too narrow of a clearance. Anything less than .040 and you can start having detonation problems which can open up a whole new can of worms, depending on the fuel you are using. The later years heads changed to a narrower dome which is a little more forgiving with pre-detonation when you start raising compression. Check your squish by inserting a small piece of solder through the spark plug hole sideways over the wrist pin until it touches the cylinder and then rotate the crank so the piston compresses the solder at TDC. Remove and measure the end of the solder.

If your squish is to small, you may want to rethink your plans for the cr head gasket depending on how much you want to spend on fuel.