Author Topic: Honda CR125R piston slap? (Read 17940 times)

Stusmoke · « **on:** June 22, 2012, 03:50:09 AM »

Hey guys, just traded the remains of my fooper for a 2001 CR125. Working, running, but I can hear a rattling noise with every stroke. I plan on keeping this one and selling my 250 depending on what my folks think. Anyway its got a rattling noise from inside the cylinder it seems, im pretty sure its piston slap whats everyone else think and what is the best course of action?

Cheers guys.

msmola2002 · « **Reply #1 on:** June 22, 2012, 05:22:56 AM »

rattling? detonation maybe? pull the top end and have a look?

Stusmoke · « **Reply #2 on:** June 22, 2012, 05:27:03 AM »

I will.

Am I going to need sealant to get it back together?
The cylinder was EXTREMELY hot for a two stroke I might add, I think hes running a fairly low octane fuel
Also, the kickstarter is VERY easy to move through its strokes. It doesn't feel like it has much compression at all.
Thanks Mola

factoryX · « **Reply #3 on:** June 22, 2012, 10:25:54 AM »

I'd do a compression test first and go from there.

Stusmoke · « **Reply #4 on:** June 22, 2012, 10:43:59 AM »

Dont have compression tester unfortunately. I could try posting up a video of it running but the audio would be terrible. Will I need a sealing agent to get the top end back together? Cos if not I'll just take the cylinder off and check out the condition of the top end. That would be much easier. Assuming I dont have to buy all new gaskets.

scotty dog · « **Reply #5 on:** June 22, 2012, 11:25:55 AM »

i had a 90 YZ 125 which used to make a rattling noise close to idle, was piston slap, cylinder was worn.
sell ya 250 Stu and bomb the 125, surely you could get enough to fully rebuild the engine, slap on some new rubber, tidy it up and youll be motoin in no time

got a pic of it??

Stusmoke · « **Reply #6 on:** June 22, 2012, 01:19:09 PM »

not yet. I'll post it up tomorrow if i remember. Tires need attending to, the seats been cut down and I'll need a new clutch cable this one feels like its made of concrete and of course, the rattling noise. But can anyone tell me if I'll need to reseal the gaskets assuming they're metal? Or will I need to buy a new gasket set and sealant just to look at it? And if it is just detonation, a simple spark plug replacement should do it right? Tomorrow I'm going to drain the fuel and put in my 98 octane just in case its a heat related issue which seems unlikely.

Super Trucker · « **Reply #7 on:** June 22, 2012, 06:20:08 PM »

Never reuse base and head gaskets. Honda cr 125,s have 2 diff. sized cylinders a and b. Even if you put a honda a size piston in a a size cylinder, the honda piston is too small, causing piston slap. The alum. frame resinates it further. A forged piston is also much louder than a cast piston. Do a google search, some riders are using Husky pistons, in there 2000-03 cr125,s. I think the Vortex piston for a cr125 is the same size as a Husky piston. There is a performance increase when you get the correct size piston. Your prob. asking your self, why did honda put the wrong size piston in, part of the reason is it,s more diff. to seize the motor, from the wrong jetting. More or less the stock piston is for break in purposes only. A play rider that never jetts his bike should stick with the stocker.

SachsGS · « **Reply #8 on:** June 22, 2012, 06:41:57 PM »

Piston skirts transfer combustion heat to the cylinder walls for cooling and when pistons get really loose blowby heats everything up.

cnrcpla · « **Reply #9 on:** June 22, 2012, 10:16:32 PM »

If you bougt the bike used its probably a good idea to do the top end anyways, unless the insides look imaculate. And judging by the description of the noise, they probably don't.

Stusmoke · « **Reply #10 on:** June 23, 2012, 01:09:46 AM »

Thanks for the advice guys I appreciate it. And I was fairly certain you should never reuse a base or head gasket, thats why I was a little confused. something else to note, when the bike first starts up it leaks coolant from the water pump, but stops after a while. So I was thinking it was something heat related and that cylinder gets bloody hot after only a couple of minutes of easy riding. Anyways I'm gonna go check the spark plug out, see if theres anything tell tale on that. If not, I guess I'll have to take the cylinder off and check the top end. Actually before I do that I think I'll drain his fuel and put in some 98. I'm not too confident hes not using shitty fuel.
When I first rode it I rode it like my 250 and it felt like my XR100... The lack of bottom and mid was insane. But once I remembered it was a 125 and got it up to the upper ranges, WOW. I took off in a cloud of dust.

Quote from: Super Trucker on June 23, 2012, 01:20:08 AM

Never reuse base and head gaskets. Honda cr 125,s have 2 diff. sized cylinders a and b. Even if you put a honda a size piston in a a size cylinder, the honda piston is too small, causing piston slap. The alum. frame resinates it further. A forged piston is also much louder than a cast piston. Do a google search, some riders are using Husky pistons, in there 2000-03 cr125,s. I think the Vortex piston for a cr125 is the same size as a Husky piston. There is a performance increase when you get the correct size piston. Your prob. asking your self, why did honda put the wrong size piston in, part of the reason is it,s more diff. to seize the motor, from the wrong jetting. More or less the stock piston is for break in purposes only. A play rider that never jetts his bike should stick with the stocker.

Well thanks Honda

so look into a vertex piston kit? Roger that. Cheers mate.

Cheers guys, I'll get a pic up soon to.

Jeram · « **Reply #11 on:** June 23, 2012, 02:45:12 AM »

a rattling sounds can also originate from wrongly adjusted powervalve cables that allow the powervalve to slap up and down freely

luthier269 · « **Reply #12 on:** June 23, 2012, 02:49:57 AM »

2001 does not have power valve cables.

Stusmoke · « **Reply #13 on:** June 23, 2012, 04:50:03 AM »

now I face a new issue; theres coolant leaking fiercely from the pump out of a tiny little circular hole that looks like its meant to be there. I also discovered that it didn't have any coolant in it at all, which worries me now because if there was no coolant in it when it was being ridden, which was for about 2 or less minutes, that the cylinder has expanded and thats whats causing the piston slap. However I noticed the coolant leak when I was riding so there was still coolant leaking then, which means there was a little bit of coolant. Thoughts?

Thanks

TMKIWI · « **Reply #14 on:** June 23, 2012, 05:43:56 AM »

The hole where the coolent is draining from is supposed to be there.
You have leaking water pump seals.
Check your gearbox oil for water as well.
Rule of thumb with any bike I buy is do not trust the previous owner.
Put fresh fuel in straight away, check all fluids and then fire it up.

By the sounds of it stu I would pull the barrel of as a bare minimum and go from there.
You are going to need a water pump seal kit as well.
Best you fix everything now before it turns to custard.

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Author Topic: Honda CR125R piston slap? (Read 17940 times)