Topic: Do I need To Bore These Cylinders?

[liPPy]

Block is from a stuck motor that had a piston rusted in place.

I've honed each cylinder and had the bores measured.

Everything is in spec, including the pistons, but there is still a residual amount of surface pitting which I hope is evident from the pictures. They are very, very shallow but i can feel them beneath the tip of my finger.

My instinct says they probably need to be bored but I'm no expert and would rather avoid the cost of the bore + new pistons if I can.

The other two cylinders are perfect by the way.

Opinions please and thank you in advance.

   

[dave500]

if you can feel it id bore them,are you keeping this bike?

[wrenchmuch]

They need a bore . New rings will wear out quickly if there are any pits left in the cylinder walls .

[liPPy]

Thanks peeps.

Yes, I'm keeping the bike.

Any recommendations on a machinist in Chicago's West Suburbs???

[Frostyboy]

It's pretty hard to tell from a photo. Are those actually pit marks? Is there a ridge at the top of the bore. I'd probably run a hone through them before boring just to see if they cleaned up.

[Skunk Stripe]

I would assume a ball hone is best? How much material will that actually remove?

[wrenchmuch]

How much is removed depends on how long you hone . You should generally hone until the ridge left by the top compression ring at the top of the cylinder is gone . I think the 3 arm stone type hone is better for this ( just my preference ). If the cylinder is beyond the wear limit , or your pits are still there after honing you should bore . From what I can see in the photos you need to bore .

[liPPy]

To confirm, cylinders have already been honed.

The honing improved the cylinders considerably but as the pictures show there are still some pits that remain.

And yes, they are actually pit marks. They are smooth with no sharp edges but they are pretty easy to feel with a bare finger.

As a reference this is how they looked before clean up & hone:

 

The general consensus so far seems to be that an overbore is required...

[Tim.]

I'd find another set of stock cylinders if you're looking to save money and avoid buying larger pistons.  There are a bazillion sets of cylinders out there.

[liPPy]

I'm considering this route and have already perused eBay.

Main issue is actually trusting that I am going to get a decent set of cylinders that doesn't require an overbore.

However, to be clear, am I correct in my understanding that K1-K6 & K7/K8 cylinder blocks are interchangable?

I have a K8...

[Lostboy Steve]

When I was 13 or 14 I used to Pickup Puch mopeds for free all the time. Most of them were left out in the elements for years. Many of them had cylinders that looked like yours. I would tear them down and hone the crap out of them. (Using no measuring tools at all). Then I would order new rings from some company in Holland. Long story short they would run but who knows what type of power was lost. Its hard to tell on a 2hp 2-stroke moped. You gotta remember those could be HARD spots in the metal now. So the ring will wear strange. I would definitely bore. And I might invest in some nice pistons while I'm at it.

[Tim.]

Can't help you with the interchangeability of the blocks - I'd bet they're the same.

[lucky]

Run a dinglebery (ball)  hone through them and wash them and degrease them.
Then measure them.

When you hone them move the ball hone up and down through the cylinder rapidly with the hone going a medium speed. You want a crosshatch pattern that is about 60º=70º angle .

After they are very clean and hone THEN measure them. But most mechanics do not own the proper tools to measure cylinders. Either buy the tools (expensive), or take them to a machine shop to measure them. Take the written  specs with you.

Don't forget to look at the ring lands of the pistons.

How many miles were on the bike?