2fun what happened is i sezed the motor at the dunes and then i hade to rebuild it so i put a new piston and ring's in but i just let it warm up once and then took of on it so what would you preferre. i know i should have more compression what is your input
thanx
Rusty

 

it has been maybe three months since the rebuild i just had to hone it out and not bore it out so would i have to hone it out again or will it be ok

 

I am having a hard tim efollowing you, but if I follow you correctly, you didn't break in the motor properly 3 months ago, and you are now unhappy with the compression, so you want to install a new set of rings?

If this is the case, you will need to hone the cylinder (assuming there is no scoring on the cylinder wall) as well as get a new set of rings.
Any time you get a new set of rings, the cylinder needs to be honed.

In your case, the piston is probably ok (hourly wise). It should however be inspected for scoring, etc.

Then take the fresh honed cylinder and fresh rings and go through the break-in procedure outlined above with NON-synthetic oil.

I am unsure if this is what you are asking.

Hopefully I answered your question.

As a side note, you MUST be certain that you are jetted correctly! Jetting that is off may make you think you don't have enough compression!

On that note, why is it that you are unhappy with the compression?[img]i/expressions/face-icon-small-confused.gif[/img]

 

I'm a little confused at where this thread has gone too. That won't stop me from opening my piehole anyway. You better get acquainted with a set of micrometers and bore gauges. Depending on your honing method, type of stone used, etc. A cylinder can become quickly out of round or tapered. Also, there's many different reasons a piston can fail. Piston skirt breaking you definitely better check your clearance, it's probably excessive. "Four corner" piston scoring usually means too tight, could be a cold seizure or too tight a bore. Melting on top of piston, erosion of aluminun, especially directly under the spark plug, or at the locating pin for the rings definite sign of detonation, caused by lean mixture, too much timing advance, crappy gas, etc. Whew... think I'll stop there. Slim, why don't you bring your parts (including the failed ones) to somebody that does a lot of this kind of thing and ask them to measure it, make recommendations etc. good luck!

 

what kind of compression do you think i should have and i will cheak it before i tear into the top end
and yes you got my question. the kid i bought it from just told me he didn't break it in right just this week. We are riding buddies. but i was wondering if i would have more power if i broke it in right
Rusty

 

Usually you should be somewhere between 135ish and 170ish (This is all psi). That's a ball park guess. I've seen engines with compression ranges of 65-80psi but those were in weed eaters and snowblowers. I'm just giving you a balpark guess. Why not just do a leak down test? Anything over 30% leakage should be torn down.

 

How do you do a leak down test and how do you know if you have a 30% leak test.
any help
thanx Rusty

 

You need a leak down tester and an air compressor. I personally wouldn't go to the trouble if you don't have them already. If you feel there's a problem, first pull the exhaust and look thru the port with a light, you should be able to see the exhaust skirt and top of piston, intake cylinder wall, you can push on the rings and feel if they are stuck. You should be able to see most obvious kinds of damage if you look carefully. If you see no damage and you still feel there's a problem, do a compression test. It may be hard to find out exactly what you're supposed to have as there are so many variables that effect this. If it's obviously low, under 130, tear it down and look for things you could have missed with your exhaust port inspection, like evidence of detonation around ring locating pins on the piston, wore out rings (do a ring end gap clearance), out of spec cylinder taper, bore size etc. As to the break in issue, There's a couple of suggestions on this thread that are as good as any. I don't see the exact procedure as making a lot of difference. It's much more important what you start out with, and that no physical damage was done, like cold seizure or detonation.

 

1st off, if you've got a 310 ESR kit, it had better have a hell of a lot more than 130 PSI.

The Stock 250R's are around 160-170 with a low reading inaccurate compression gauge.

Speaking of compression testers, thats a whole other can of worms. If you don't have one of the more expensive compression testers (like Snap-On), you are wasting your time if you think the pressure read is the actual cylinder pressure! The only reason a cheaper one should be used, is to compare what the reading on YOUR motor was with a fresh bore, compared to the SAME cylinder after "X" amount of hours have been put on it. A cheaper compression gauge is not good for anything but comparing the two readings on the SAME motor. You would in that case want to see how much compression had dropped over time with extensive hours.

I will see if I can find my write-up on compression testers, and I will post it here.

 

Here is a write-up I did a couple of weeks ago. Hope this helps.



We've all (or most of us anyway) heard the term "compression testing you motor".

What many people don't realize (as I didn't either for a long time), is that simply going out and buying a compression tester and slapping it in the sparkplug hole may not give you the correct reading you think it might.

There are many things that need to be taken into consideration when compression testing a motor.

One of them is the length of the compression tester tip.
The tester tip should match the length of the sparkplug tip that is used in your motor as recommended by the manufaturer.

Another thing to try to avoid are attachments such as thread adapters that will effectively increase the volume of the head, thereby reducing the the pressure read. (the actual pressure in the cylinder will be higher than indicated on the gauge).

Avoid the rubber style "push into the sparkplug hole and then hold it" compression testers. These are inaccurate at best, and often cannot seal the pressure of many high pressure set-ups.

Cheap compression testers (screw in type) will not give you true cylinder pressure readings, HOWEVER, they CAN be used for comparison purposes to determin if rings are getting worn AS LONG AS THE SAME TESTER AND FITTINGS WERE USED WHEN THE MOTOR WAS FRESH, AND READINGS WERE WRITTEN DOWN.

Just adding one adapter can reduce the reading by 20 lbs or more!!

The "best" compression tester to use, is the "Snap-on" line of testers.

They have the schrader valve inside the tip itself, and are very accurate when taking pressure readings.

So next time you hear someone say they have "X" amount of lbs of cylinder pressure, or "your rings are ok if you still have "X" amount of cylinder pressure, take it with a grain of salt.

Because unless they have used the above procedure, OR have spent lots of money on a truly accurate compression tester, chances are they don't REALLY know.
Nor do most of your "average Joe" riders want to buy the expensive set-up to really know what the "actual" cylinder pressure is, or should be.