A rider ...

[Ricks]

Pete,  remove the rings from the piston. Then take the cylinder and piston and put them in the oven.  Heat until 300, then check clearance, increase in 25 degree increments until the piston seizes or 400 degrees, which ever comes first.  I have done this on 3 different motors, and have found that at 400 I have .003" clearance. This seems to be enough.

FYI, I have found that the cylinder is always tighter at the bottom then the top.

Keep after it Pete, you will get there.

[pd]

Rick ,

What ratio of oil mix do you use ?

And ,  according to your previous post , the piston grew .004" @ 400° , plus the .003" clearance at that time , equals .007" . That should be the cold piston clearance for 'safe' operation , assuming adequate lubrication .
Correct ?

Pete .

[Ricks]

Pete, piston grew .004 at 425, that is the hottest I ever tested one. 

At 400, I see around .002-.003 growth.  IMO, the cold clearance isn't important, it is the hot clearance that you need to be concerned with. 

I run 40-1, or thereabouts. Same mixture I run in my weed eater and blower.  I know Tom and some of the other guys like to run closer to 20-1.  Don't lean out the carburetor too much or you will lose cooling and lubrication.

[pd]

Too lean may be my main problem . The piston is seizing on the exhaust skirt . That means too lean . I'm running Opti2 at their recommended mix . I think that may be close to 50>1 . The carb is set at about 1 1/2 + turns out for both .  I'll double check that in the morning .

Pete .

[pd]

When tearing down my motor for seizure repair , I noticed the new rings on my new piston had seemingly drifted from the 120° position I had them set at when I put the motor together to only about 10° - 12° apart . That and the ends were directly in line with the transfer ports . Not good .
They were in the same position when I tore the motor down from the first seizure .

What might cause that ?

I'm thinking I better pin the rings while I have the motor apart .

Pete .

[pd]

Having to pin the piston rings in order to keep the ends from drifting over a port , I bought a couple of compression pins . Also called roll pins or slotted spring pins , some even call them dowel pins .

Anyway , can anyone think of a good reason not to use them in this application ?

TIA .

Pete .

[Ricks]

I don't see a problem with that, maybe a little loc-tite also?

[pd]

That or maybe a needle punch in the landing , on either side of the pin , once installed

I'm not really sold on either 'added' measure as the pin will be locked into the hole by the overlapping ring ends . And , the pin hole will be blind , as far as I can tell .  There seems to be enough material behind the landings to allow that . But , I haven't measured to be sure .

Pete .

[pd]

In the cool of this morning , I pinned the piston , using 1/4" long x 3/32" wide compression pins .

I drilled the landings above the wrist pin , but toward the rear , to a depth of about 5/32" . The pins had to be driven in , so it's unlikely that much , if any, outward drift will happen . I squared the outer end of the pins and called them 'good for service' .

Then the ring ends needed relieving to fit the pins . I used a jewelers square file to reach that 'end' .

All things considered , I think the project turned out nicely .



Now to ready the piston and cylinder for assembly . Hopefully , for the last time .

Pete .

[Ricks]

Looks good, I will be watching this test.

[pd]

Thanks , Rick .

I see it as my not having any choice but to pin the rings . Both times I took the piston out of the cylinder , the ring ends were directly in line with the transfer ports . No way could I live with that .

The only question in my mind is : will the compression pins hold up as well as solid pins .

I guess I'll find out .

Pete .

[pd]

Dang good thing this is a hobby . If it isn't one thing , it's another ...

I put the motor together and tried to start it . Spun real nice , but not fire . I pulled the plug and it's dry ; spark seems a bit weak .

I pulled the carb apart and cleaned that . Tried to start it and got a few intermediate pops .
I'll have to pull the flywheel to check what is not copacetic under there . I'm thinking that maybe the key is partially sheared due to the seizure

Pete .

[oil-lamp]

Be sure to do one thing. Shoot a little oil into the cylinder to keep it lube until it runs. That and it helps with compression in the beginning and the extra oil burns out when it runs.

[pd]

Hi Reese ,

I generally shoot a bit of WD40 into a freshly honed cylinder . It penetrates the rings/landings and does a light initial lube . It also helps the rings to seat a bit quicker , being as it is so light weight .

Pete .

[pd]

I finally had the motor running , again . But , I could not get it to accelerate and it had very little power . It wouldn't stay running for very long without constant feathering . And , once it got hot after the last test ride , it acted like it was starting to seize , again .

I honed the cylinder until there was .008" piston clearance , just prior to this last fiasco .

I pulled the compression plate and found a nice puddle of very dark fuel/oil mix in the bottom of the crankcase .
That has been true each time I removed the compression plate since before the 'Wayne bore' .

That begs the question : how can I have a flooding problem , with the piston skirts and inside soaked in fuel/oil mix , and simultaneously have seizures ?

The float needle is not doing it's job . There are times I can see fuel dripping out of the air filter housing . And , the carb adjustment settings have to be set much leaner than any that have been suggested here . A bit over half a turn on the idle screw and about a full turn on the needle valve screw . Those lean settings and a flooding go hand in hand and likely why the motor doesn't accelerate .

I took a cylinder compression reading : right at 100 pounds .

The ring pinning has held nicely , so far . But , there isn't more than an hour run time involved .