CR85 NO BOTTOM END POWER

[oldmx]

My son has a 2003 CR85. Recently the piston skirt broke while riding. Cylinder wasn't damaged. New piston, rings, wristpin, and head gaskets were installed. Now the bike has no bottom end power. It cranks and idles fine, but when you try and take off in 1st gear you have to rev the engine and dump the clutch to get it going, then if you don't feather the clutch and rev it up to keep it going it bogs down and will die.

Top end power and speed is great. It is much stronger and faster, compared to prior to piston failure.

Prior to failure I was running oil/gas mixture of 50:1. Prior owner of bike said he had always ran it that way. Now after piston failure I am running 32:1.

It had normal bottom end power prior to the piston failure. I bought the bike used several months ago so I don't know if it was an original or aftermarket piston that broke. It has ran fine for several months.

I have since changed the crankshaft oil seal on flywheel side. I have checked the engine for air leaks and don't find any. I have tried different jetting setups, new spark plugs, and new air filter.

I read that the cylinders on the 2003 CR85's were recalled. I checked with my local Honda dealer, he checked the VIN number and found that the recall work has been performed on the bike.

Could the reed valve cause this problem?

Any other ideas?

Any and all advice is appreciated.

[oldmx]

One more question. If a piece of the skirt lodged in the passage way between the crank case and the cylinder, could that cause this problem (no bottom end power)?

[dhighlan]

I would start out making sure the carb is clear of any obstruction and check the reeds thoroghly, seated flat and no cracks. Did you do a complete leakdown test or a compression test? There is a great thread from Faded on building and using a leak down tester if you search for it.
One last thing how does the plug look?

[ossagp]

Since I never blame oil ratios for anything this may sound strange, but why not mix up some of the old mix and run it and see? Though 50-1 sounds really light to me for an 80, it would tell you where the low end might have gone so you can at least quit looking for mechanical things and start tuning around it.

In the meantime, and since there is no power valve to go leaking on yours during a bleed down test, take Dhi's advice and build that leakdown tester.

I do my leakdown tests with an air regulator (this one is from a paint sprayer) and just hold a pressure and use soapy water to find leaks on the power valved bikes.

[oldmx]

Last night I put a new set of reeds in it. The old ones looked fine to my untrained eye. No cracks or freyed ends that I could see. Both reeds seemed to be touching everywhere. I installed new Boysen reeds. It made a small improvement, but it still bogs down, requireing you to slip the clutch and rev the engine to take off from a dead start, or to increase speed while rolling along at about 5mph.

The spark plug is buring pretty clean with a slight amount of blackish oil residue around the electrode.

This afternoon I will try a 50:1 premix and see what happens. If this doesn't identify the problem I will move on to the engine pressure test.

Thanks

[ossagp]

Oldmx. You just demonstrated something alltogether unrelated to the main reason that you posted: Fresh reeds make a difference. I don't do it as often as I used to, but on the reeds that are reversible, you can flip them over (just like you turn a push broom around) and help keep that freshness. I used to do it really regularly, especially on the metal ones.

[oldmx]

Scratch off 2 more possibilities. I drained the tank, mixed a 50:1 mixture and ran it. No significant change.

Next I removed the carb. Cleaned it out thorougly. It was very clean to start with. Checked all jets, they are the original jet sizes. Clip is was/is at original setting, 2nd from top.

Next on my list is a pressure test.

[oldmx]

And the results of the pressure test shows:

Cracked case, literally, not solved case, but cracked case!

[dhighlan]

Sorry to hear that but, at least you know instead of chasing the jetting around. That's way the leakdown thread from Faded is invaluable. You could chase you tail for weeks before figuring this out.

[saulo]

Hi guys,
Dont be so ungry with crankcase crack.
J&B weld will solve completely your problem.
I used in my YZF-250 and its running like Chad Reed last bike!!!
Hope helped

[oldmx]

Saulo, how long have you been running with the JB weld? What is the crank case made of? Can it be welded?

Thanks

[stormbringer]

The cases are cast aluminum

Yes, they can be welded, but only by a highly skilled welder.

Cast aluminum is not easy to weld, but it can be done.

How big is the crack?

I bet that JB weld will work fine for a long time.

[oldmx]

I don't know how big the crack is. I havent taken the motor apart yet. I did a leak test yesterday and found that air is coming out of the oil fill plug hole as fast as I supply it to the cylinder.

[dhighlan]

That sounds like a seal and not a crack in the case.

[dhighlan]

Are you loosing any oil?

[yz250guy]

Originally Posted by oldmx

air is coming out of the oil fill plug hole as fast as I supply it to the cylinder.

Put the plug back in...

Sorry man, I couldn't resist. Good luck.

[stormbringer]

Well I don't think you have a crack in the case then.

I would suspect the right side crankshaft seal.

[oldmx]

yz250 guy, I set myself up for that one. Very nicely done!

I don't know if the bike is losing any oil. The outside of the case is completely dry. The bike is not smoking when its running. I will drain the oil and measure it to see how much oil is in it after 3 weeks of running it trying to find the problem.

I hope its only a crank case seal. Is it common to leak so bad? I can't even put 1psi of pressure on the case its leaking so much.

I'm assuming its a crack in the case between the tranny and crank case section because when the piston broke several pieces went into the engine, but I guess it has the same chance of tearing up a seal, maybe more.

[dhighlan]

I thought about you saying how you threw a shirt on the piston after my response so that has me a little concerned. If you are not burning oil you may have a crack in the case above the oil level on the clutch side, right below the cylinder. This would explain feeling the air so directly at the fill plug but not using much oil. I would take off the crackcase cover and pressure test it again and you will see the problem immediately.

[oldmx]

dhighlan,

Good idea. I'll pull the crank case cover this weekend, pressure test and see what I find. I assumed a crack up high, above the oil level also. Are there any seals up high that aren't submerged in oil, that would only leak air, not oil?