piston crown

[Moto Squid]

I took off the head just to check things out and I found that the burn pattern on the piston was quite odd. What can be concluded from the pics?? For not knowing much I'd guess the combustion process isn't efficient as it could be....

and the bike is an 02 cr125 with Vforce, thin base gasket and twin head gaskets with a moded head (unkown specs) bolted ontop, oil is amsoil @ 32:1

 

[Moto Squid]

exhaust side is top of pic

 

[Moto Squid]

photo 2

 

[Rich Rohrich]

Scavenging is pretty skewed. It looks like the transfers would benefit from proper porting.

Lots of carbon tends to be a sign of too rich jetting or low combustion chamber temps (usually from running to rich or low loads). The oil and fuel you use will also contribute to the deposits. Clean fuel and the proper oil will keep things much cleaner.

 

[Glitch]

oops, I take too long to write and look at pics. Rich posted while I was typing. Rich, That exhaust side of the piston looks pitted to me, if it is, what would cause that? I thought that pitting was from detonation.

 

[Rich Rohrich]

I can't tell if it's pitted, but if it is detonation is a likely cause.

 

[UKcr125rider]

This is the burn pattern from my '03cr125. I consider it to be about right. Hope this link works

 

[MikeS]

Seen those pits before. Detonation for sure. Leaning out at WOT, Overheat, Squish to tight, Poor fuel, Timing.

What was done to the head.?
What fuel have you used ?

Amsoil will leave very little deposits when jetted and timed correctly with a top quality racefuel. The burn pattern will be a tad greyish and almost not visible. Other oils will give that mocha color.

 

[Moto Squid]

The exhaust side was a concern of mine. I put it back together with the stock head and one head gasket. A quick zip around the yard shows that it pulls stronger but I'm unsure if that is only because of the increased compression or if that moded head wasn't what I thought. Either way I'll get a good load test of this new setup at the track tomorrow. What would be the symptoms of detonation?

I try and use Amaco premium lately, but not always
I have no clue as what's been done to the head...it was something like $15 off ebay so I figured what the heck.

About the weird intake pattern, I have the Vforce with the 99 intake manifold like Marcus did but did not match the manifold to the block to get rid of any overhang or mismatching. Could that be causing excess turbulence?

 

[Rich Rohrich]

Originally posted by Moto Squid
About the weird intake pattern, I have the Vforce with the 99 intake manifold like Marcus did but did not match the manifold to the block to get rid of any overhang or mismatching. Could that be causing excess turbulence?

No.

 

[steve125]

Also keep a close eye on head gaskets on the Cr's. As they start to blow, the symptoms will be eratic running, coolant over flow and excessive pressure or a big pop sound when removing the cap after the engine is cooled down. Looks like on the exhaust side front you were getting close Moto Squid. Look for the black gasket coating being burned away and this will lead to a coolant passage. This means a blown head gasket and will surely lead to detonation. It may be why that piston area is so clean(coolant) and appears to be pitted(detonation) as water is entering the cylinder at that point.

 

[Moto Squid]

Now that I took it back apart I think Steve125 is on the right path. Towards the intake side where the piston has that very clean spot I noticed a small little scratch on the jug from the water passage to the cylinder wall..ah ha!! Problem #1, but how do I fix that? I have had small coolant loss issues lately...my simple mind finally just put one and one together. Problem #2 is the burning of the coating on the head gaskets. The pictures show fairly well that half of the coating between the water passage and cylinder is gone. Would 2 gaskets be more prone to this? I've got my old gasket from winter and it shows practically no burning. The exhaust side of the piston does not feel rough at all, in fact it is very smooth. I'll start out with one new head gasket and see what happens.

 

[jmics19067]

noticed a small little scratch on the jug from the water passage to the cylinder wall..ah ha!! Problem #1, but how do I fix that?

You can try a plate of glass setting on your work bench with a sheet of 280 or 320 grit wet and dry sand paper laying flat on the glass. Carefully remove the studs from your cylinder and with a healthy dose of light oil<wd40 or something> lay the cylinder on the wet paper. Without twisting or rocking it move the cylinder in little figure 8 motions across the paper. I repeat do not rock the cylinder and keep adding fresh oil. If you are careful and patient you can true a lot of sealing surfaces this way from minor imperfections.

You can also try a product called "Copper Coat" a spray on gasket adhesive that is mostly copper designed for steel head gaskets. The stuff works real well but it is not as good as a flat sealing surface

 

[Moto Squid]

With some decent track time I found that it will pull a gear higher in a lot of places :yeehaw: I did a compression test and have just over 150 which is tons better than a weak 120 with two gaskets. Time to mess with race gas!! Around what psi does it become mandatory for high octane?