Cylinder ding + carbon?

Callil Capuozzo /

Hi guys, I've been battling an air leak between carb and intake and what I think is blow-by so I got a bunch of carbon buildup on my piston head. When I disassembled to clean the piston head off, I decided to take a look at the cylinder to make sure everything was ok. Looks like a small ding in the wall, previous owner said it had soft seized before.

How bad is this and what is the best way to take care of this: re-hone, new ring and the works? Will I need a new piston?

see pic

bike deets:

magnum - za50 2 speed

15 bing - 90jet

mlm exhaust

polini kit - well worn (thousand miles maybe?)


Re: Cylinder ding + carbon?

Callil Capuozzo /

ok, well I've done some digging and it seems like a light sanding with very fine sandpaper to smooth out the ding should work, then give it a hone and new piston ring. after, new gasket and gentle break in should do the trick.

let me know if this sounds solid

Re: Cylinder ding + carbon?

Probably Fred /

Yeah that's not good looks like seized from incorrect high timing and it looks like there's scoring on other parts of your cylinder wall too.

I have cylinders that have 5000 miles on it that look perfect. That Cylinder looks horrible for only thousand miles.

You may have more blow by but if it runs run it.

Set your timing low to start like 14degrees btdc to run below 400 degrees f on head temp gauge running full throttle for a few minutes. If you don't back off or you can seize again. Add timing more timing if you run cool.

Re: Cylinder ding + carbon?

Callil Capuozzo /

Thanks Ken, will give that a shot.

I should clean up the cylinder before doing timing stuff right?

Re: Cylinder ding + carbon?

Callil Capuozzo /

I took another look this morn and noticed that the ding in the cylinder might be worse than I thought, seems to be an actual pit through the nikasil plating.

I'll definitely try to get it running but do you think it might be doomed from the start?

better pics attached.


Re: Cylinder ding + carbon?

Probably Fred /

Ya that piston is bad You kinda got ripped

What you need is a new polini kit

I wouldn't waste my time getting a new piston and trying it out in Cylinder. The intake tongue looks bent too.

They sell more and more kits every day because dummies seize them from high timing/ not watching temps.

Re: Cylinder ding + carbon?

That is a chip in the plating. Technically you could say that the cylinder is junk. That said the chip is below the ring, so it wont affect compression. You could run it until it blows up, but you would risk all the trash making a mess of the bottom end. The piston is wrecked also, it looks like it lost a section of the skirt. Since it's a plated kit you cant bore it, and honing will do little to help your situation. You basically need a new kit.

Re: Cylinder ding + carbon?

Callil Capuozzo /

Thanks for the feedback, you guys are da best.

I'm surprised how well it was running with all this damage, definitely low power, but moving fine for a while so I didn't think to check. lesson learned to buy without knowing much about the bike :/ I guess it's near pointless to try to make it workI suppose I have some decisions to make.

I have a pretty nice stock e50 from a friend, I could do a rebuild, new bearings etc. and swap onto the bike and just run stock for a while


buy the kit and do it right with temp gauge, correct timing etc.

Re: Cylinder ding + carbon?

Tyler Jaynes /

Just run it until it blows, Polini kits have a sweet spot as far as reliable blasting goes and once you deviate from that spot the damage to the cylinder tends to end up in the point of no return. Just try and learn a little tuning and such while it stills runs and when you get a new one you'll have a better understanding of whats going on in there and your kit will last longer.

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