028 AV Super project

[flatsfisher]

finished putting a KS NOS top end kit in my new to me 036 Super a few weeks ago. decided I needed another project LOL. picked this up an hour ago from FB marketplace about 30 minutes from home. when I pull the starter, it is hard to pull and feels sticky, but the piston goes up and down. gotta be from a near seize or bad crank bearings? can't wait to pull this apart. bar and chain are brand new, maybe 1 use.

 

[flatsfisher]

looking in the exhaust port it looks like the ring is stuck in the piston. still got 150psi though. odd. by the serial number looks like a 1984 model give or take.

 

[flatsfisher]

installed block plates and did a good cleaning. was pretty grimey, which a good 38 year old saw should be.

 

[flatsfisher]

def trashed the exhaust side. intake side looks good. the crank, crank bearings and rod are in fantastic condition. there is a very small amount of aluminum deposit on the cylinder wall and only on the exhaust side. no gouges. no damage to the head, just some carbon deposit as expected.

does this look like a lean seize or a straight gas seize to you guys?

 

[flatsfisher]

 

[Maintenance supervisor]

Staight gas, especially if it has good seals, maybe lean if there's a hole in the impulse line or fuel line.
Great saw, one of the best all around saws made. Bottom end looks pretty dry too.

 

[Jasonrkba]

You sure got that rascal clean.

 

[Mad Professor]

What does ex port look like? There is a fair amount of dark material around top of piston and between the rings.

May not be cause but carbon scoring may have played a role.

 

[Brushswamper523]

Man I just did one of this that the crank seals and bearings were bad. I got it done literally this week. I love the saw it was my first bottom end rebuild. I hope your rebuild will be as fun as mine was.
Here is the finished product.

 

[flatsfisher]

wow, that looks new. what differences are there between the wood boss and the AV Super?

 

[flatsfisher]

What does ex port look like? There is a fair amount of dark material around top of piston and between the rings.

May not be cause but carbon scoring may have played a role.

will post a photo this evening. will be out riding all day today.

 

[flatsfisher]

What does ex port look like? There is a fair amount of dark material around top of piston and between the rings.

May not be cause but carbon scoring may have played a role.

sorry, I was out all day with my 40hp 125cc 2 stroke.



here is the exhaust port. I think you may be right. there is a lot of carbon build up in that port.

 

[Mad Professor]

sorry, I was out all day with my 40hp 125cc 2 stroke.
View attachment 1003668


here is the exhaust port. I think you may be right. there is a lot of carbon build up in that port.
View attachment 1003667

Good chance it's carbon scores. Was running too rich, or wrong oil (like outboard or for water cooled), and the carbon flakes off.

Did it pass press/vac tests?

 

[flatsfisher]

I should have done those tests before I took it apart but with the damage, I didn't think the tests would work. I think I will put it back together and do those tests tomorrow. the base gasket did not tear when I took it apart so should still work for testing, I think.

 

[Maintenance supervisor]

wow, that looks new. what differences are there between the wood boss and the AV Super?

The 028 came in 3 flavors, 42mm ,44mm,and 46mm being the super with a factory pop up piston. Some early models have no chain brake.

 

[Mad Professor]

I should have done those tests before I took it apart but with the damage, I didn't think the tests would work. I think I will put it back together and do those tests tomorrow. the base gasket did not tear when I took it apart so should still work for testing, I think.

Scored piston won't effect a pres/vac test.

I'd do seals anyway as it's a 35 year old saw. BR400 uses same seals, and a gasket set costs less than seals individually. The 028 set is NLA.

 

[flatsfisher]

so, it passed the pressure and vacuum tests with flying colors.

 

[flatsfisher]

I de-carboned the exhaust port.

 

[flatsfisher]

removed the tiny speck of aluminum transfer and scrubbed the bore.

 

[flatsfisher]

so, I think this cylinder is in fine shape. I want to get a NOS piston kit with rings, 10mm wrist pin, and circlips and a new OEM wrist pin bearing and base gasket.

I want to make sure the new piston is the right size for the wear of the bore. I used a snap gauge and micrometer to measure the cylinder bore. just above the exhaust port it measures 45.99mm and below the exhaust port 46.00mm. I cleaned the top of the melted piston, and it is marked "C". is the "C" indicative of the piston diameter? the cylinder is also marked "C".