Cylinder clearance

[Noobi06]

I am sending in my cylinder for replating. Since I am riding on roads, they adviced me to have my cylinder 0.1mm larger than the piston. Usually, you have about 0.05mm. This is to prevent the rings/piston from catching the wall (heat pinch). It happens sometimes on the road when you switch gears and a lot of people have gotten it when driving up hills etc.
What do you guys think about it? He says it is good and I understand his reasoning, however I am scared that I will loose power.
How much horsepower do you think I will loose? I have about 39 and I do not want to loose too much.
However It will be safer for riding. Can it give other consequences?
Thanks guuys

 

[Darkside]

I'll admit, I have never heard of that. what would road riding have any difference to dirt riding in terms of the engine? personally, I would stick with the factory recommended clearances.

 

[Anders]

Road riding will in many cases mean longer periods with wide open throttle, hence higher mean temperature.

A125cc ridden by a youngster on the roads is usually ridden harder than you would do off road.

Sent fra min YAL-L21 via Tapatalk

 

[SS109]

I have never seen nor felt the need to increase piston to cylinder clearance for running a 2T dirt bike on the road. Lots of my club members dual sport and/or have their 250/300's street plated here in Arizona. We've done highway miles and fast dirt roads and I've never seen any bike seize up running stock clearances and on some bikes running as little as 60:1 fuel/oil ratios. The key is in your jetting. Always be on the rich side if you plan on dual sporting your 2T.

 

[Noobi06]

Do you guys think I should do what he adviced? 0.1mm clearance. This would decrease the risk off heat pinch. According to him, many with the same gasgas ec 125 have driven like 60kmh and from nowhere gotten a pinch so I assume it would be a great idea.
I just dont want to "throw away power". At the same time, its for the better

 

[SS109]

For a 125, maybe it is a good idea. I might increase it a bit but what they're recommending just seems excessive to me. I would think .07 or .08 and those are some big clearances IMO/IME. I guess, however, I would defer to them if they have actual real world experience with the Gasser 125's.

 

[Noobi06]

Thanks for the answer. Ill got in the middle at about 0.075

 

[Darkside]

with more clearance you might get more piston slap. especially as it wears. might need to replace the rings more often

 

[Noobi06]

Yeah I was thinking that aswell

 

[Noobi06]

Okey so apparently the cylinder has a cast iron lining which is really bad. We are going to replate it either way and I am going to run a forged piston inside. Bore is going to be 54.5 and piston is going to be 53.5 or 54, something like that.
Now what I wonder is how bad this cast iron lining is? Its an old way of doing this that some owner had done.
How much will it affect the lifetime of my cylinder/pistons?

 

[(F5)]

All bores used to be iron. But cast over in manufacture. The old school repair was to bore out and fit a liner once the iron bore was too worn for reboring.

Even shrunk in the interface is not as good for heat transfer. But, hey, it kinda works and you are stuck with it if you cant get a new barrel.

Plating works well on ally. But needs special techniques to stick properly to iron. I guess many platers will have learnt these by now. Basically mask ally, acid etch the iron, and plate with far more current than you would with ally.

If they have done many barrels like this successfully (ask) then I'd take his recommendation to the letter.

 

[Noobi06]

Okey will do. Im just afraid that
1. Its going to run very hot and possibly heat pinch.
2. Im afraid that its going to decrease the lifetime of my pistons, and giving me large risk for seizing. He told me theres a chance the pistons might only last 50h, but with forged pistons it might be regular lifetime.

 

[SS109]

Wow, now that recommended large clearance makes sense to me. Personally, I would try to find another cylinder but I know those are tough to find. Go by what they're recommending and, like F5 said, follow everything to the letter!

 

[Zman]

The GG125 has a plated cylinder.

 

[(F5)]

Yes. He said that it has been sleeved by a previous owner.

 

[Noobi06]

Ok, so it was cheaper to sleeve the cylinder, so thats what some dumb owner did. On top of the sleeve, they put nikasil replating.
So I am going to replate that but of course the replating affects the temperature and lifetimes of the pistons.
I am going to run a clearance on 0.1 instead of 0.05 since these bikes are really common to heat pinch/seize when running even throttle on roads. A lot of people have driven 50kmh in traffic and from no where the bike stops.