Author Topic: 2001 TM RAcing 125mx Piston meltdown (Read 9839 times)

metal_miracle · « **Reply #15 on:** July 13, 2012, 09:10:46 PM »

tm come stock whit base gaskets in 4 sizes in the gasket kits..

maybe you got the thinest of them

thmike · « **Reply #16 on:** July 14, 2012, 07:06:06 AM »

i think I got more than 4 gaskets. I went with the thickest base gasket..lol

Jeram · « **Reply #17 on:** July 15, 2012, 01:57:51 AM »

forget about the base gaskets.

1. head shape (knowledgable 2T tuners can fix this for you and wont cost much), think its under 100 bucks? and if you dont like the way it performs with the new head shape you can weld it back up and remachine to take it back to exactly how it used to be. 100% reversible.

I think a few people on here will be able to recommend a decent 2T tuner in the US to do this work for you cheaply.

2. jetting

3. ignition timing (maybe or maybe not needed)

let us know how it goes!

beaner · « **Reply #18 on:** July 15, 2012, 12:56:52 PM »

What I would do is this:
Talk to the previous owner and find out why he was using race fuel in it. Maybe he knows something you don't.
People saying you need to do something about the squish is premature. You need to baseline the bike first and do a little research to determine if they are prone to preignition or detonation, and find out from the previous owner is he's made some modification that is making it this way. You made at least 2 mistakes. You didn't run the race fuel AND leaned out the jetting based on "feel". One will compound the other if you're borderline detonating. If you put it back together, make sure you have the correct piston, check the timing, double check for any air leaks (including seals), return the jetting to stock, and do a compression check to make sure you don't have some super high compression numbers. Once you know for sure what you have, then you can decide what to do with it.

SachsGS · « **Reply #19 on:** July 15, 2012, 02:52:50 PM »

It's been my experience that many/most TMs require higher octane fuel then can be found at automotive gas pumps.

TMKIWI · « **Reply #20 on:** July 16, 2012, 07:49:50 AM »

Quote from: SachsGS on July 15, 2012, 09:52:50 PM

It's been my experience that many/most TMs require higher octane fuel then can be found at automotive gas pumps.

X2.

I could get a head mod done on mine to run pump gas but like the smell of avgas too much.

TM's have higher compression then the standard japper.

thmike · « **Reply #21 on:** July 16, 2012, 09:49:50 AM »

Previous owner..one of my best friends back home. (I joined the military and went back home on leave and this bike was in the shed collecting dust because of cranks bearings were starting to fail so I took it back with me as a project). He always ran 50/50 race gas because he said it always ran better. Said it had alittle pinging when not running race gas and that rings lasted longer when running race gas mix. He raced the bike back when it was new and til about 06. It was pretty muched parked in 06. The base gasket that was in it was the second thinnest base gasket. So I thought/hoping running a thicker base gasket would keep me from running race/pump gas. I guess I was wrong. I was told by a TM guy that it may be possible to run a thicker base gasket and lower the compression since TMs like running higher octane then what you can get at the pump here. I've been doing some research and found out if my squish is to big that it can also cause the same problems I had. So I'm thinking about going with the same thickness base gasket that was in it, jetting it back to stock, 175main vs 172main that in it and try and retard timing 1-3 degrees to get away from detanation. And I'm trying to save money by not getting the head cut but looks like if it doesn't run well after this and i'm getting detanation I will get the head cut.
He always ran 50:1 with synthetic oil and I'm running 32:1 with Maxima Castor 927. I'm also guessing because the bike was leaned out for 50:1 and race/pump gas that it may be alittle lean

This didn't happen on 2 short rides by the way. I rode it all day at the track one day. Then all day the week after trail riding. So about 2-3 hours on the bike when it happen. I just ordered a wossner piston today.

TMKIWI · « **Reply #22 on:** July 17, 2012, 08:22:24 AM »

If you are running 32:1 you are running leaner then he was.
More oil , less fuel.

beaner · « **Reply #23 on:** July 17, 2012, 01:31:36 PM »

Quote from: TMKIWI on July 17, 2012, 03:22:24 PM

If you are running 32:1 you are running leaner then he was.
More oil , less fuel.

Technically this is true, but the difference is, at 50-1 you're running 98% fuel to oil (some of which will also aid combustion), and at 32-1 about 97% fuel. 1 percent seems like an insignificant difference, but how do you accurately convert this difference to a jet size?

Jeram · « **Reply #24 on:** July 18, 2012, 02:04:53 AM »

yeah, my theory is that biggest issue with changing premix ratio is the fuel viscocity, which restricts the flow through the jets slightly.

when you compound this with the 1% change due to the fuel volumes it starts to add up perhaps to a few percent.

TMKIWI · « **Reply #25 on:** July 18, 2012, 08:01:20 AM »

Quote from: beaner on July 17, 2012, 08:31:36 PM

Technically this is true, but the difference is, at 50-1 you're running 98% fuel to oil (some of which will also aid combustion), and at 32-1 about 97% fuel. 1 percent seems like an insignificant difference, but how do you accurately convert this difference to a jet size?

Yeh I know but if the bike was on the lean side to start with and running lower octane fuel it might have bean the tipping point.
TM's love octane.

thmike · « **Reply #26 on:** July 18, 2012, 09:11:43 AM »

I've got a new piston and rings on the way. As well as jets(175 &178). Hopefully I can get some higher octane fuel before I leave for my Michigan trip. I'm taking both of my bikes to Michigan to do some racing and visiting family. I'm in the USAF and stationed down in florida. I also bought some parts to put a new ring in the YZ125. Figured I'd do it just to be safe. She's been great and I got it a few months ago with almost no hours on it.

I'm going to retard the timing some on the TM and hopefully have some race gas for it also. I have a buddy whos going out with his friend on a Cigar boat, one of the race looking boats and he said he could get me some 114 or 110..can't remember. If its 114 i'm going to mix it with premium 3:1. 110 will be 2:1. I'm hoping for the best anyways. I'll ride it one day at the track and take the head off to inspect the piston once i'm done with the first few rides. And if it looks crappy then it will be 50/50 or getting the head modded. I think that may be my best bet but for now I'm trying to keep the budget low. I already has about 700 into this bike. But it is a TM.

TotalNZ · « **Reply #27 on:** July 18, 2012, 10:23:06 AM »

Hmmm my TM runs fine on 95 RON straight from the pump, that was with 1.5mm of squish from the factory. Although i've just tightened that up too 1.1mm this latest rebuild and have yet to try it, she's up around 140psi now on my shitty cheap compression tester.
I've been told should still be ok on pump gas but i'm thinking i'm gonna have to start mixing 50/50 av gas.

2T Institute · « **Reply #28 on:** July 18, 2012, 10:45:38 AM »

Run much better at 0.7mm squish with reshaped combustion chamber.

TotalNZ · « **Reply #29 on:** July 18, 2012, 10:50:44 AM »

Quote from: 2T Institute on July 18, 2012, 05:45:38 PM

Run much better at 0.7mm squish with reshaped combustion chamber.

Yep thats what i'm thinking too, finding someone over here to do the work is another matter.
Might end up sending it over to you 2T.

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Author Topic: 2001 TM RAcing 125mx Piston meltdown (Read 9839 times)