Pattern piston kit install - advice needed

[DaveyCrockett]

It is possible the rod is bent, did the piston slide up and down freely with no rings? Does it slide easily with rings? Does it only get tight when bolted down? Does the cylinder rock from side to side if the bolts are loosened up and the flywheel is pulled over gently?

 

What brand is the kit? I would only trust one brand of aftermarket kit 100%!

 

The piston slides without rings. Bolting down makes no difference and it seems to heave evenly on all the bolts loosened two turns with rings fitted.

 

The name on the kit is WAR TECH, supplied by Garden Hire Spares (GHS).

 

I tried measuring ring gap. The first ring fitted at the base of the cylinder had zero ring gap, so I think this is the trouble.

 

Would 12 thou be a good target?

 

Thanks for the good advice.

[spudulike]

Try 5 -7 thou min and it should be fine, sounds like this is your trouble though. It is just the risk you get on cheaper kits and need a bit more care in checking and fitting.

[DaveyCrockett]

Thanks for the help Spud and all who replied.

[peatff]

I'd put a bit of a radius on the port edges as well, I found they sometimes come not very well finished.

[openspaceman]

It's a new cylinder - part of a kit.

 

Sorry I misread your original post.

 

I have seldom had to scrap a OEM nikasil cylinder, they normally survive seizures and only become U/S when gouged by a broken ring or other foreign object

[spudulike]

One last bit of advice, make sure the ring ends fit under the retaining pin well and the ring end can be pushed just past the centre of the pin so the ring ends are a snug fit with the pin.

Often the ring ends are poorly formed and there is bruised metal or swarf around the retaining pin. All these faults will do you no favours!

[spudulike]

I'd put a bit of a radius on the port edges as well, I found they sometimes come not very well finished.

 

And that is good advice, had to do it on OEM parts before now!

[DaveyCrockett]

I'm not sure I have all the tools to smooth off ports. I don't think they spent much time finishing off the casting in China. It's especially horrid around the impulse port. I've had a little go with needle files. I have got a die grinder in the cupboard but have never really used it. I'm guessing I would need to buy some burrs. I've got a few mounted points but not sure that's the thing to use. I've never done any work on engine internals, just fitted parts together, so please forgive my high level of ignorance.

 

The pot is on now, but I'm waiting for more parts from my very slow local Stihl dealer, so might be prepared to have a go.

[DaveyCrockett]

Openspaceman, If I'd known I would have just got a piston, but I read that Stihl don't sell them alone, so thought I had to buy a kit, and price drove me East.

 

My OEM cylinder doesn't seem too bad.

 

Tried giving it a scrape with some brass, but that wasn't too effective, so tried Plusgas and 600 grade wet and dry which was a bit better.

 

What is the right way to clean it up? I'm just trying random stuff here!

Edited May 28, 2016 by DaveyCrockett

[spudulike]

You can use acid or alkaline solutions or 180 grit lowering to 400 grit if the transfer is minimal. You will still need to use abrasive paper if chemicals are used but it is easier on the plating.