A rider ...

[pd]

I just popped the crank bearings out and after they landed on the bench , I looked at that suspect crack . It showed up as very dark and a lot closer to crack looking . I'll have it tigged .

Something I hadn't noticed the last time I had those bearings out was tool marks . Like someone had tried to remove the bearings with the case cold . They aren't real bad and they are located along the outer edges of the intake channel .

Pete .

[carryall]

 TIG welding on an Aluminium engine case can sometimes be quite the challenge.  I've done it on a couple occasions and remember on one occasion I had to drill small holes at the ends to stop "chasing" the crack, and needing to "V" it out for both decent penetration and in order to clean the oil contaminants from the pores of the casting.  Usually the preheating of the area will suffice tho.  That would be nice if that ends up being the problem.  Fingers crossed for your success!

[pd]

Spent a little time cleaning / smoothing passages in the case and the cylinder . Evened the exhaust ports as close as I could get them . The intake ports aren't nearly as far different like the exhaust were . If I had extended grinding 'bits' I would straighten the intakes . But , being as they are pretty close , I'll leave them alone , for now .

Tomorrow I'll see if I can find someone that can tig the 'crack' .

Pete .

[pd]

Time for new crank bearings . I left the case in the 'oven' too long and the bearings turned blue .

One bearing just fell out , like normal , but the other must have gotten a smidgen cockeyed and I had to 'help' it escape .

Always something . Can only blame myself .
I hate when that happens .

Pete .

[pd]

Opinions Please :

Advantages or Disadvantages of having sealed bearings on the crankshaft , both main and right side bearings .

It seems that there would be a little less bottom end volume if the bearings were to be left sealed .
I don't think having sealed bearings would change intake much , but maybe a bit more vacuum

I'd still run the crank seal if that bearing were to be sealed . Maybe that would increase the overall sealing 'properties' at that end of the crank .

Pete .

[pd]

More than a month has passed and not a single response to my request . And , a very simple request at that .

At the risk of being the fool , I'll post another request :

How far below the bottom of the exhaust port does your front piston skirt rest at the top of the stroke ?

Does anyone know what that measurement should be ?

TIA .

Pete .

[Ricks]

Opinions Please :

Advantages or Disadvantages of having sealed bearings on the crankshaft , both main and right side bearings .

It seems that there would be a little less bottom end volume if the bearings were to be left sealed .
I don't think having sealed bearings would change intake much , but maybe a bit more vacuum

I'd still run the crank seal if that bearing were to be sealed . Maybe that would increase the overall sealing 'properties' at that end of the crank .

Pete .

I don't think it would make any noticeable difference.

[Ricks]

More than a month has passed and not a single response to my request . And , a very simple request at that .

At the risk of being the fool , I'll post another request :

How far below the bottom of the exhaust port does your front piston skirt rest at the top of the stroke ?

Does anyone know what that measurement should be ?

TIA .

Pete .

I have not the slightest idea! Not sure why it would matter?

[pd]

Thanks for the response , Rick .

The reason I ask about skirt closure of the exhaust port is :

1st - I know my exhaust ports were drilled 'uneven' . That's poor workmanship and could easily have an effect on the swirl pattern of the gases , both entering and exiting the combustion chamber . How much

2nd - We know that any 'leak' in the bottom end has dire effects on performance .
 
So , why wouldn't a not totally closed exhaust port to the bottom end have an effect , at least on fuel transfer ? As soon as the port opens on the up stroke , any vacuum is gone and any pressure has to be re-established .

I'm thinking that's why I can't get the motor to start with the kicker . It turns too slow and not long enough to build fuel transfer pressure . When I use power to start , the motor has to spin about twice as long as with the kicker before it starts , albeit only with the idle set just below transmission engagement . Much lower and it wants to die and I can't get it to smooth out .

Hopefully all that^ makes some sense .

Pete .

[Ricks]

Pete, as long as it covers the exhaust port, what difference does it make by how much?  Isn't that the question you were asking?

[pd]

Agreed , Rick .

'IF' the skirt covers the port , there should be no or very little pressure loss .

My skirt does not fully cover the exhaust port , on one side .

I'm thinking about making a copper base gasket that would allow the cylinder to sit higher and the port to be closed . I'd have lower compression which may not be good , depending on how much .
That copper would have to be thicker than the paper I'm using now , in order to do any good .

Pete .

[Ricks]

Pete, I admit that I have never even thought to check for that.  Next time I build a motor I will try to remember to check.  I have used a longer rod in 2 motors without issue though.  I would think if this was a problem, it would show up then.  This was with Wayne's piston also.

[pd]

I don't normally check that either , Rick .
And , I didn't specifically check it this time . I was checking the top of the ports to be sure they were close enough to even with the top edge of the piston . While running the piston through it's full stroke , I noticed the 'gap' below the skirt .
Maybe I am just lucky enough to have gotten a Monday morning or late Friday afternoon cylinder .

The longer rods are .030" longer , if I recall correctly . That's .76 mm . The 'gap' I'm dealing with is a couple of mm , maybe a bit more ? I don't have a good way to measure . Blade type feeler gauges just won't work .

The fact that a longer rod can be used and still perform correctly tells me that the skirt must overlap the bottom of the exhaust port by a bit more than .030" in order to 'seal' .

Anyway , I'll be adding that check to my list of checks on 2 stroke motors .

Pete .

[pd]

This morning , I wrapped my piston with waxed paper and inserted it into the cylinder . A couple of thicknesses of waxed paper makes for a real tight fit .

Then I applied a couple of decent sized 'dabs' of JB Weld to the lower portions of the exhaust ports . I'd prepped the ports for this yesterday by cleaning and scoring any surface that would have JB Weld applied .

After letting the JB set up to a state not fully cured , I worked it down to were the ports would be totally closed when the piston is dead stopped at the top of the cylinder . That will insure enough skirt coverage for a decent seal of the ports at the top of a normal stroke , by at least .030" .
I'd trued the base gasket surfaces previously , so the extra coverage by the JB should be adequate .

I'll leave the JB alone for a day to get a full cure before a light hone and re-assembly of the motor .

Pete .

[Ricks]

You are braver than I am. I would not be that confident that the JB weld will hold up to the heat cycles and could break off with disastrous results.  I hope I am wrong.  Good luck!