CRF250 Compression (PSI)

[forsaken]

Dose anyone know what compression my CRF250R should be running. I have removed the auto decompression off the cam to get an accurate reading and I am getting around 97psi. Dose this seem right

[moto_x2005]

hahaha good enough, least its not zero

[ndekens]

Sounds low to me. I remember doing a compression test on my old 58 chevy truck and got around 135psi and im pretty sure its not running 12:1 pistions. Does your bike seem to be lacking in power? does your oil smell like gas? How many hours are on the bike? Anyway if it aint broke, break it then fix it.

[forsaken]

Haha.. i only just bought it and i found oil in the radiator after a few rides. its not lacking any power. i flushed the radiator several times and went back to where i bought it from and they said the oil was from a head that they just replaced. there hasent been any more oil in the radiator and its not blowing smoke im just a little concerned about spending all this money buying a new bike and finding out the head is gone. its an 05 so it shouldent have done too many hours. But who knows

[skipn8r]

The 250X manual lists something like 157 psi. The X has the same compression ratio and a different cam so the compression will be different, but 97 seems pretty low.

[forsaken]

hrmmm.. i really dont know what to do. where i bought it from said if there was something wrong that they would fix it although i dont want to stuff them arround.. possibly it is just the cam. i would have though at 97psi it would run preatty bad but it seems ok. possibly it would be best to just leave it?

[skipn8r]

If you have a competent Honda shop near by, one of the techs ought to be able to tell you the compression on a healthy 250R. Maybe someone here on TT can put a compression gage on a stock, healthy R and post results?

[spizz5]

Are you holding the throttle wide open when checking?

[forsaken]

I'm not holding the throttle.. Should i be? that shouldn't make a difference... should it? I defiantly think that the best way would be to test it on a second bike.. also i haven't done a wet test as of yet.. maybe i should do that and see what i get. So how would you generally test for faults on the bike.. testing the compression doesn't seem to be something that is generally done.

[Motocross26]

When doing a compression test, hold the throttle wide open.

[nc250x]

The 250X manual lists something like 157 psi. The X has the same compression ratio and a different cam so the compression will be different, but 97 seems pretty low.

Don't know about the 157, but according to the 250X service manual (page 8-7) the compression should be 57psi

Instructions:

• Warm up the engine

• Stop Engine and remove spark plug

• Connect compression guage

• Open throttle all the way and crank the engine

• Continue untill the compression reading stops rising (4-7 seconds)

Low Compression Causes:

• Valve adjustment needed

• Valve Leakage

• Blown head gasket

• Worn piston rings

High Compression Causes:

• Carbon deposits on piston head or combustion chamber

• Faulty decompressor cam

-Ryan

[forsaken]

Excellent, Thanks for that.. i will try it and see what i get

[moto_x2005]

57 psi,? but isnt his bike reading 97 or somethin? wow damn ur about ready to blow ur head off the cylinder if thats so

[forsaken]

if it said 57 PSI would be with the auto decompression on the cam still. if you remove the valve cover there is a small device that you removed to get a correct reading. Its on there so you can start the bike without snapping off your leg. on the right side of the cam there is a 8mm bold that you remove and pull out the auto decompression. At 57 PSI i don't think the bike would even start. I would have though that 140 - 180 would be right, although I haven't done a lot with bikes only cars

[WA_trail_rider]

I'm not holding the throttle.. Should i be? that shouldn't make a difference... should it?

If you think about the amount of engine braking that you get from a closed throttle --- why wouldn't a closed throttle throw off a compression test? And (with engine running) opening the throttle causes wonderful things to happen. I wouldn't discount the effect of a closed throttle on a compression test.

If you do it again - you might try it both ways and report back on the forum, I'm curious what the difference might be. Especially since 57psi generally means MAJOR engine failure .... and you say it runs good.....

[forsaken]

i will to a test tonight and get the results on here within a few hours

[forsaken]

OK.. Here are the results

Dry Test (Throttle off): 97 PSI

Dry Test (Throttle on): 97 PSI

Dry Test (With Auto Decompression on): 50 PSI

Wet Test (Throttle off): 100 PSI

Here are a few pic's of the Auto decompression that the Honda uses etc

http://members.westnet.com.au/forsaken/images/hondacam/cam1.jpg

http://members.westnet.com.au/forsaken/images/hondacam/cam2.jpg

http://members.westnet.com.au/forsaken/images/hondacam/cam3.jpg

http://members.westnet.com.au/forsaken/images/hondacam/testing.jpg

I'm guessing that 97 PSI is about right although if there is anyone who would like to test there bike to confirm or if there is anything else that could be tested if you would like to let me know it would be good.

[skipn8r]

Don't know about the 157, but according to the 250X service manual (page 8-7) the compression should be 57psi

Oops. That's what I get for recalling without verifying. 57 psi @ 800 RPM. I'd say your engine sounds good !

[HancockMX546]

I have an 08 crf250r that I am pretty sure has a worn out top end. I haven't run a compression check, as my compression gauge is made for larger engines and I need an adapter, but the shop in town said it was running 46 psi. I adjusted the valves, which were super tight. Does anyone know what the cold compression should be, if there's any difference between cold and hot compression?

Thanks

[John Daroza]

On 11/5/2005 at 4:53 PM, forsaken said:

Dose anyone know what compression my CRF250R should be running. I have removed the auto decompression off the cam to get an accurate reading and I am getting around 97psi. Dose this seem right

No at 13 to 1 or 5 will be up there.

Depending on overlap of the cam.

My 11.1 to 5 made 185 psi.

It had overlap and you can't test the engine spinning up.

I will guess from 15 to 20 psi at 8000 rpm increase in PSI.

Normal engines run about 130 psi. Low in 90 psi . Below 90 not good.