Cuyuna 440 rebuild.

[stingerss427]

Hi all, I'm thinking I am going to have to rebuild the 440 in my TKX and I have a few questions.

 Are the cylinders chromed or iron sleeved?

 I've heard that the lower ends have had issues of not sealing between the halves. Is this a real issue that I will need to be concerned with?

 Any hints on getting some more power out of it. Porting? Plane the heads? Exhaust? Carb/carbs? Intake (loose the air box)?

 I'm new to the Scorpions and was hoping some of the people more familiar with making these things really run good would be willing to give a few hints. I was really impressed with the way these things can go. At Princeton this summer there was one that was really kicking butt in the grass drags, led me to pick this TKX up. I have liked the looks, but seeing how they run really pushed me to this sled.

 Thanks, Tim

[obj1]

Hey Tim, yes these little engines run well. A "first time" re-build will challenge you. Us guys on here will help anyway we can, however there is a lot of cuyuna discussion on this site and the V.S site. Look through all the related posts and you will gain tons of knowledge. Then, ask alot of questions and enjoy some german engineering!

[weverat]

If you can put it back together bone stock, to where it makes the original HP as designed, and do a good job of clutching, you will have a winner.

If you mod the porting or anything, it will need a different pipe etc.

You can certainly do some port matching, and trim the gaskets as needed so everything flows real good. Play with different thickness base and head gaskets to get the compression you want, little things like that, and they run strong. But to win, it is all about the clutch!

One of my best race engines has never been apart, it is a factory assembled engine, but it does have a comet 102, somewhat dialed in for grass drags.

Yes, I agree with OBJ, the Cuyunas are not all that user friendly to assemble, seems to take me all day every time. And that is after cleaning parts, chasing threads, replacing studs etc.


You have to re-torque everything every other day for about two weeks, as the little 8mm studs sticking out of the cylinder both ways will only handle 17 ft pounds, and then they stretch. So leave the motor mount plate off, till case half studs have been re-torqued several times.

Keep us posted, and enjoy!

[stingerss427]

Good thing to know on the lower end. The snowmobile engines are new to me. I've been rebuilding small and big block Chevys for years so I'm familiar with wrenching. Reading and trying to grasp the the two stroke idea with port sizes and port timing. It doesn't appear to be to difficult of a concept, but there is more to it than the basic air/fuel in, fire, exhaust out idea.
Thanks for the help, feel free to keep the suggestions coming.

[stingerss427]

Went to Waconis swap. I got lucky and found a 79 Cuyuna 440 from a TKX. It was complete with the clutch and manifolds, missing the rewind and the carb and needs a rebuild. Moves freely. For the money I thought it would be a good place to start. Ordered up a couple gasket and seal kits today. What have you guys run for pistons? I have not been hearing much good about the Wiseco pistons, but no one really throwing out much for praise on any others. Also, how expensive is it to replace the center crank seal? Doesn't appear to be an easy thing.

[stingerss427]

I see that another post here recently is speaking OK of SPI. Any others that anyone has good luck with?

[weverat]

SPI and Parts unlimited pistons are good. Sometimes you have to grind the inside of the piston a bit in order to make the wrist pin bearing and thrust washers fit. Kind of typical with all aftermarket parts now days, nothing seams to be exactly right, but close enough to make it work.

Yes, the center seal is a lot of work as you have to split the crank, and the seal is hard to find. Seams to me there is a thread on here where Kube1 found a seal that works.

I have never replaced one, ben lucky to have cranks with good center seals. It certainly helps to start with the latest model Cuyuna you can find. Some of that old stuff is 45 years old, and bound to have bad center seals.

scorpionsleds.proboards.com/thread/852/whip-resurrection?page=1

Here is a thread concerning center seal repair, I do not know where to get the original seal.

[junkman]

Feb 1, 2016 13:51:21 GMT -5 stingerss427 said:

Went to Waconis swap. I got lucky and found a 79 Cuyuna 440 from a TKX. It was complete with the clutch and manifolds, missing the rewind and the carb and needs a rebuild. Moves freely. For the money I thought it would be a good place to start. Ordered up a couple gasket and seal kits today. What have you guys run for pistons? I have not been hearing much good about the Wiseco pistons, but no one really throwing out much for praise on any others. Also, how expensive is it to replace the center crank seal? Doesn't appear to be an easy thing.

Huh, I sold a motor just like that at waconia...............Small world. 

[stingerss427]

Junk an, are you the guy with all the ElTigre hoods?

[junkman]

Feb 2, 2016 20:57:18 GMT -5 stingerss427 said:

Junk an, are you the guy with all the ElTigre hoods?

Yes, that was me. 

[stingerss427]

I'm the guy who bought the Cuyuna from you.

[junkman]

Feb 3, 2016 0:07:15 GMT -5 stingerss427 said:

I'm the guy who bought the Cuyuna from you.

Thats what I figured. Like I said, it was a strong running motor till the piston went. It should run good with the rebuild. 

[stingerss427]

Well I finally got to it and tore into the 440. I took it all apart. Hot tanked the case halves, jugs, and heads, taped off the mating surfaces and blasted with aluminum oxide, then hot tanked again. Then I did some intake and exhaust gasket matched porting. Trued up the head mating surface. Trued up the case halves, removing the absolute least amount of material. Ported the area between the cooling fins on the mag side head. New Pistons, rings, gaskets, and seals.

Now the issue I'm having is the timing. I reinstalled the mag and flywheel. Set the points at .014. Used my dial indicator to find top dead center. I put a piece of spark plug box in between the opposite set of points so I wouldn't get residual power to the light. While holding the advance open I turned the flywheel counter clockwise waiting for the timing light ( made from a 6 volt camping flashlight ) to dim. I have turned it way past the manuals .082-.102 before tdc before it dims. I have the stator plate turned as far as I can clockwise. I have tried positioning the plate in several different areas and it doesn't seem to get any better. I am really confused at this point. Any help would be appreciated.

[obj1]

Very tough to explain procedure. I can say this. Take out piece of plug box from points. Put stator back to middle of slot. And...I dont care about point gap. Its when they open/close that makes me smile.

[kerry]

Gonna keep an eye on this thread too!

[stingerss427]

I opened the gap and moved the plate to the mid point. It was definitely better. I'll puts with it more tomorrow and see if I get lucky. It'll have to be luck, because obviously it won't be my smarts.

Thanks Tom!

Also the midpoint in regard to the bolt and slot are not even.

Attachments:

[weverat]

Turn the flywheel counter clockwise far enough to close the points and then clockwise until the points just crack open. I like to use a multi meter set on buzz.

You can adjust the timing by moving the stator plate for one side, for the other you will change the point gap. I know you are at .014 now, but you can be .012 to .016

I hold it in the advance position with my finger. Almost all my stator plates wind up with the slot very close to as far retarded as you can get. But i run my timing on the low side of the spec.

[stingerss427]

Ok, now I'm starting to confuse myself even more. I have been checking the net for the timing numbers as in the piston height before tdc. I have seen several specs so who do I believe? I have seen .082-.102, .082-.112., .102-.112, and .110-.125. So far with my messing around the .110-.125 is the closest range I have gotten too. Where have you guys been? With the plate at a total clockwise, not holding the timing advance, the light reaches full brightness at the point the flywheel mark lines up with the casting mark "run". Then when I push the advance lever the light goes out.

[kerry]

Under the reference material of this website there is a section called books manuals  documentation etc. It has a cuyuna timing procedure page there.I just read it and it is clearer on how to do the timing.I understand the order which to do it now.Thought I would pass this along.
Kerry

[stingerss427]

That is the same one as I have. I see in the notes there is a .104-.124 measurement. I went with the full .124 and I turned the plate to full retard, point gap at .017 , and with a pin in the advance I am at the max. I sure hope that isn't too far advanced. I suppose at this point the same only other thing is to add a thousandth or two to the points.