How much compression should I have ??

[250girl]

Ok, so my Dad and I just rebuilt a 1986 RM250. We put all sorts of new parts and stuff in it, so it should be running like new( even though in my opinion it isn't). So we did a compression test on it and came up with 160.

Now, my old WR250(2-stroke !!) has started acting up. It will start and I can get it to about the top of the driveway and then it completely stops running. I asked around, and I found out that it hasn't been rebuilt in at least 6 years, maybe 7 or 8, and I have been riding it hard and steady for about 2 years, and before that who knows. So we did a compression test on it and came up with 225 !!! On a worn out old WR !! :uh:

So I need to know, what should the compresion be on these bikes?

 

[polaris4x4er]

my yz250 has about 180 and i have been told that they are good till about 135 and im pretty sure that 4 strokes have way more compression then 2 strokes.

 

[250girl]

Just to clear things up, my WR is a 2-stroke. Up until 1997 (8?) they were all 2-strokes.

 

[CarnageZ28]

If it was me I would be kicking the bike over to top dead center and then pulling the cylinder head. Sounds to me as if you may have excessive carbon built up in the combustion chamber/on the piston.

This will spike compression ratios through the roof. Make them HARD to kick. And most importantly, causes detonation ( The ignition, from the excessive heat of compression, of the air fuel mixture well BEFORE the spark would normally occur; causing the piston to have to fight against these forces on its way to the top of the compression stroke ) which WILL grenade the top end. The piston can only handle so much.

Also, will cause bike to run hot, feel weak, and stall out frequently.

Now on the flip side of things, you said that it hasnt been rebuilt in years. Once you clean away all the carbon, etc. The rings are liable to be worn/shot anyways and it might not start from LACK of compression. If it was me, I would be pulling the head, and cylinder and replacing the top end with that many years on it.

Good luck

 

[whenfoxforks-ruled]

What Carnage said. Pull up your sleeves and get to work. Pictures would be nice. 225 seems way high for a wr. 160 on a rebuild, how much time is on the motor?

 

[250girl]

Thank you CarnageZ28,
That is pretty much what the WR has been doing. We have it apart now, and there is carbon in all sorts of bad places, it's even built up on the reeds. And that bike has been impossible to kick since I started riding it 3 years ago, my dad and I are the only ones who can start the evil thing. But lately is when I really started noticing an unusual lack of power, and then it started randomly stalling, and not wanting to start again. As for what we are going to do to the bike, new piston, replate the cylinder(it has damage), new bearings and seals, and maybe even a new crankshaft(ouch).

Whenfoxforksruled, I have no clue how many hours are on the bike. It spent a few years sitting around here being taken on maybe a dozen short, and very slow rides. Then I started riding it a little bit very gently( it was my forst exerience on anything bigger than a rt100) and for the last 2 years I've ridden the heck out of that poor bike. As I said before, I have no clue what happened with it prior to our purchasing it.

About pictures, I will get some, but I don't think it will let me post them here or in the gallery.

One more question, Carnage Z28, do you by any chance drive a Z28 Camero ?

 

[CarnageZ28]

95' Z28, 6-Speed, Convertible. I bought it totaled when I was 16, finished totally restoring it by myself when I was 17, and the R-Title back to me a month or so before high school graduation. It was totaled in 96' and sat in a garage until I bought it so it only had 10K miles on it. Now has almost 20K on it.

Mods: Long tube headers, off-road Y pipe, 3" cut-out, Blowmaster muffler, Cold Air Intake, custom grind camshaft (224/230 .600/.600 108+2), 1.6 Roller Rockers, Comp Bee Hive valve springs, comp hi-tech pushrods, trickflow guideplates, Mallory ignition box.

I am waiting to find a cheap old lap top to use to finish off the tune on it. I had PCMforLess tune it for me, however there is more left in it, and with the cam, there are some driveability issues I want to work out of it before I put my nitrous kit on it.

Pretty neat car, lots of hours of labor, and lots of $$$ spent. But its well worth it. Seeing a "new" styled car rumble and lope like old school muscle, and have no problem laying a good 100 foot strip of rubber from a 20 mile an hour roll... :p ... Satisfying, just, satisfying ...