New Pk80j 66cc Teardown

[210061741]

Well i got the new motor on tuesday.
I promised i'd take it apart and i did.
I found many things that put big smiles on my face.
Got some good pics, i will try to keep it short and sweet.

If this should be a photo album or some other kinda post please let me know.

 

[210061741]

The Top End

8 MM Head Studs either Stainless or Crome Plated.

The piston wrist pin is drilled out a little larger than iv'e seen before and the hole is actually in the center of the pin.

Standard Needle bearing at the wrist pin, The main bearings have a manufacturer identification mark so i should be able to find out the quality of the bearings easily enough. Chineese / Japaneese
I'm positive they would use only one bearing supplier so we will assume all the bearings in the motor came from the same place.

The piston rings are coated with something.... ( I don't know what )

The piston itself has a Dome shape head which gives higher compression and more surface area for pulling heat out of the motor.

The piston even has oil holes drilled in the bosses where the wristpin goes.

It is also marked on the top with a 5 at the exhaust side and an arrow pointing which direction to install it. ( points from intake toward Exhaust )

Put the piston in wrong and you could land the Ring ends and Pins in a port which would sooner or later break a ring.

Also the ring locating pins are at the intake side of the motor which helps with the problem of loosing a pin caused by a large exhaust port.

The jug is very well engineered. A little of casting flash was in there but other than that it is looking good.

The exhaust port is up high and the transfer ports sit a little lower than the top of the exhaust port.
It is also shaped very nicely not just an oval going just about straight through the jug.

The intake port is quite low and very nicely angled toward the top of the piston. It is also clear of the piston skirt at TDC.

Both ports taper from large outside to smaller toward the cylinder. "PERFECT"

All of the ports are very large and have some very distinctive angles going into the cylinder.

I really like the porting in this jug. Seems to lead me to believe this will be a top performer.

Even the transfer ports have a nice widened port at the cylinder walls.

Hard to get good pictures inside there... too much glare from the crome plating. I think it's crome.

The slant head itself will need a little working over.
Several small scratches and nicks in the sealing surface.
I planned on milling it on the Glass / Sandpaper anyway and that'll all clean up.

Also there were 2 head gaskets installed.

If anyone wants a picture of a particular part that isn't shown clearly enough let me know before i put it back together. ( Soon )

 

[Dilly Bar Rob]

Good to see that this engine indeed looks half decent on the inside (have never had either of mine apart yet-knock on wood).

I thought that the PK/zoombicycles engines were of the "bottom of the barrel" variety (based on a report from Don Grube about the factory where they are assembled...), I guess you can't believe everything you read.

So it has a needle bearing on the wrist pin? I thought that all PK engines had a bushing (at least I was kinda' hoping that mine did-they seem to be more reliable in the long run)...

Looks like all PK80's come with the 2 headgaskets installed.

 

[210061741]

The Bottom End

The ****ershat bearings are 6202 - 2RS. (sprocket shaft)
Shielded and Sealed on both sides = no lube required.
I'll still pack grease in the clutch post hole.

Antother very nice feature, i noticed a thrust washer behind the sprocket and a thick heavy duty rubber seal behind it.
No more dirty chain from the engine. That bearing is sealed on both sides + an extra seal in front.

The transfers in the crankcase are nice and smoothe.
No big step like others i have seen.
Actually ground my last motor just like it.

It also has the extra wide 40 mm front mount for large downtubes.
(no drilling)

The crankshaft and connecting rod look like the usual but i found out looks are very decieving.

The only thing i didnt like here is there are no oil holes drilled in the con rod small end. (easy enough to fix)

Ther rest is allmost unbelievable.

Standard 5 pc crank with the rough machined flwwheels.

Until i looked at the big end.

The crank pin is drilled out hollow
(helps reduce that extra weight from the heavy 66cc piston assy)

Now for the grand finally.

I was checking out the conn rod big end to look for oil holes.
First i noticed "Hey this thing has thrust washers at the needle bearing"
I spun the rod around to expose the slit in the con rod for oil.
To my astonishment this baby dosen't have a caged needle bearing on the big end.

It has Crowded needle rollers. (Awsem) there the best !!!

Now if they were at the piston wrist pin that would be even better.
But even at the crank thats a bonus.
Much less slop in the con rod vs my other motor.
And thoose needles should never fail.
Wear yes Fail Completly NEVER.
No more K16x21x10 roller bearings for me.

The thing about crouded needle bearings is there very hard to assemble.
Theres no cage to keep the needles from going all over.
I think thats why most use the caged bearing.
I've heard assembling a crowded roller is enough to make a grown man cry.

Also in one of Fabian's post there is a writeup about the better crowded needle bearings. ( that they are the correct ones to use )

Supposedly only found in old generation StarFire Engines.
Guess not no more my engine has a production date of 6 / 2009

Yippie
I absolutly could not be happier.

 

[210061741]

Dilly Bar Rob

I believe there are several categories of engines out there.
Allthough they might all be PK engines. (variation depends on production date)

Maybe some vendors gets a substancial price break on a Blemished Engine.

I guess it would depend on there source.

This one came from Pirate Cycles.

It is a PK80J Limited Edition Slant Head.

It reminds me of Grubee famous GT4 Go Sickem.

As far as Don advertisement. " apparently he was worried for a reason "
Anyway there were apparent hammer marks in my 6202 bearings of my Grubee

I didnt see any marks on this PK.

I would reccoment anyone with the know how to dissassemble ther engine and clean it up before you ever run it.

There was alot of metal particales all throughout and some sharp enges.

Other than that this motor is the cream of the crop.

I hope i can get me a few more.

 

[iron_monkey]

What other motors have you observed? Is this the only motor you seen with the special crowded bottom end bearing?

 

[210061741]

Iron_Monkey

I have a Grubee GT-2B 48cc with about 2000 miles on it.
Hard miles 6000 / 8000 rpm all day.
It has taken my abuse very well.
I bought it cause they were supposed to be the best.

I have worked on engines alot of my life.
I have a Mechanical Engineering Degree and a un-buyable 12 years of machining experience.

Any way i have another thread around here "1500 mile teardown"
If you wnat to see the pics.

I have spent countless hours studying every aspect of the HT Motors.
It is easy for me to see that his PK will run circles around my Grubee.

Actually i pulled the Jug off the Grubee today cause i decided to use the PK needle bearing at the piston wristpin.

I orderd a few Sthil chainsaw bearings to replace the standard HT bearings so i figured i'd get some use out of it.

When i pulled the needle out of the Grubee it fell apart.
4 needles came loose from the cage.

It was when i tried to put the PK bearing in the Grubee piston that i realized the Grubee bearing was 10MM wide and the PK was 13mm.

Obviously i'd prefer the 13mm wide bearing.

It was a little too big so i filed down the bosses inside the piston to give enough clearence. Put it back together and well see how it runs tommorow.

I can say one thing for sure.
I like the quality of the components in the PK much better than the Grubee.
But thats my opinion.

Most of the HT's ive heard have K16X21X10 for the crank bearing.
Thats what the grubee has.

The crowdede rollers are much better.
So is this PK

 

[210061741]

Mann guys i figured you would really like to know what the difference between motors really is.

Not too much response on this one.

I put much time and effort into bringing post like this here.

Sometimes it feels like i wasted my time.

It would be nice to see you guys add what you have found in your engines.

Maybe some other opinions would help also.

I'm not perfect as hard as i try to be.

So a little help is much appreciated.

 

[sportscarpat]

Teardown

210061741,
I have just introduced myself to this forum so I could reply to your thread. I read every bit of your post and have looked at some of your other posts as well. You are not wasting your time with your efforts around here. I am looking into a second build and want to find the best and most powerful 2 stroke I can get my hands on without going to the custom tear down rebuild guys. I can do that myself. I have also spent years working on and around engines and feel I know what I am doing. You look to have a great deal of experience, as well. I saw that you were looking at the new Grube "GoSickem" on another thread you started, but now see you went with the PK80. Was this because of availability? I may go with the Grube and buy all the parts and assemble myself as you said in your other post that you could not buy the complete engine in the states due to the EPA. So, in your opinion (which I value), which engine will have more power? Does this PK80 have the wider intake and exhaust ports? By the way, I ported the intake and exhaust on my Grube 80cc and it made the engine much smoother. I also threw on the performance CNS carb and it ran smoother still, a little slower at the bottom end, but smoother and nicer running.
Thanks for your efforts to keep us informed.

 

[professor]

I never knew that the needle brgs. that lacked a cage were called "crowded".
I am looking at the HTs even though they are not legal here- fascinating design.
Thanks for the post.