'84 Tecate Crank Stuffing and Rebuild w/ pics

[81Rmachine]

So my Kawi chewed up a crank and when I went to rebuild it I thought I'd try to bring it up to date with some of the newer dirt bike engines I've had apart. Just about everything made since late 80's early 90's has some sort of nylon stuffers in the lightening holes. Honda has the whole counterweights wrapped in sheet metal all in an effort to decrease crankcase volume. I realize this has all been discussed but I hadnt heard of anyone actually trying it so Ill see what this does. In theory a decreased crankcase volume should create a greater vacuum as the piston travels up to pull more air through the reeds. It should also build more pressure as the piston travels down to shove more air through the transfers thus making the engine more powerful and giving it more throttle response.
So... Heres the pics!
Heres the crank fresh outta the engine, as you can see in the 4th pic the one thrust wash was completely shredded.

I started to press it apart with a bearing seperator between the 2 halves but it was taking so much force and no go so in order to prevent distorting my crank webs I cut through the rod and pin, and pushed the pin out of each half.

If you look at each web you can see how the inside of each is hollow and it goes in about 1.5 to 2 inches on each one so before i pressed it back together I took a dremel with a sanding wheel and cleaned out each hole real well and cleaned them out with brake clean and then some soap and water. I heated some JB weld and heated the crank halves and with the epoxy heated it poured like syrup and i filled each hole from the bottom up into the hollow area in the center of each web to take up a decent amount of volume. If you look close at the first pic where the rod pin is in one side you can see the epoxy in the center.

One crank half was slightly bigger dia. then the other so i put that side down and when I was ready to press on the other half i used the press to hold each half square and then used a straight edge and swung the top half side to side until I had the same gap on either side with the straight edge across the counterweights. I got very lucky, I was expecting to do some truing with a brass but when i threw it up on V-blocks I had .0005 runout on the drive side and .0003 on the flywheel side. The Kawi service manual spec is .0011 if you convert it to std so that was plenty good for me as i didnt want to make it worse.
So now that the crank was rebuilt and true the only other thing left to address was the ends of the rod pin and the lightening holes, so I ordered up some nylon round stock, the same thing in OE cranks, and turned it down to a have a .005 press fit in each bore. I pressed them in with red loctite and the gauge on the press read about 1 ton of force so they're not going anywhere. I made each one .050 shorter than each counterweight and put a 45 deg chamfer for adequate rod clearance. You can see how they stick out and while i could've made em shorter I wanted to take up as much volume as possible.
The next question I had before doing this was obviously balance, and I weighed absolutely everything for rotating and reciprocating mass and figured out a bobweight just as if I were balancing a V8 crank and there was a slight difference in weight that I wasnt worried at all about especially seeing as how these singles use a much higher balance factor than the common 50% on a V8. They have very heavy counterweights to cancel more reciprocating mass and reduce up and down vibrations for more front to back. Heres pics of turning and installing...

Questions and comments welcome, sorry if this post got a bit long but atleast there's pics to keep you interested, Ill post my results once its running here shortly!

[El Camexican]

Way cool project. I admire people who are willing to experiment with their engines.

I do have a couple of questions. The first is about what you call “lightening holes”. I was under the impression that those holes are put there to facilitate aligning the crank halves when pressing the rod pin in at the factory more so than as a method of reducing weight or balancing the crank. If you know more about that please share it.

In photo 15 is that the nylon plugs protruding into the space between the two halves and if so how close does the rod come to them? Looks tight. You mention that most engines come with them and while I agree that they seem to be on a lot of engines, yet my 2002 KTM 300 does not have them. I did a little case stuffing on that engine and was considering filling those holes, but didn’t. Now you have me thinking…

So what else to do have planned for that engine?

[81Rmachine]

Thanks El Camexican, What I was referring to as lightening holes I had originally thought were aligning holes too, just as you mentioned. Upon closer inspection i could see they were just rough drilled and they weren't even drilled straight through. One hole in particular measured .785 on one side and .801 on the other. The surface finish in the bore was rough torn steel from a dull drill bit. It wasn't even drilled quite all the way through, there was a lip I had to grind out before I drove in the plugs. The main thing that led me away from believing these were alignment holes was the fact that you could see the edge of the con rod when you looked through them which would require grinding a flat spot in your pin for clearance which would make it loose in the bore and basically obsolete. I actually wanted to turn a pin to make assembly faster before I actually did look at it closely.

"In photo 15 is that the nylon plugs protruding into the space between the two halves and if so how close does the rod come to them? Looks tight."

With the nylon plug pressed flush with the outside of the counterweight, there is .050 clearance to the rod as this is how much shorter I made the plugs, and your right it does look pretty close but nothing to worry about.

"You mention that most engines come with them and while I agree that they seem to be on a lot of engines, yet my 2002 KTM 300 does not have them. I did a little case stuffing on that engine and was considering filling those holes, but didn’t. Now you have me thinking... "

I've never had a KTM apart myself so thats interesting to hear, It may just make a noticeable difference, Im curious to see how much of a difference ill see with the tecate. My main bike is an '03 CR250 which is due for a top end soon, and I've read that bike responds well to crankcase stuffing, but with that bike apparently the extra volume is in the crankcase itself which im guessing is what you had stuffed on your KTM? This Kawi really didn't have any space to fill in the case, everything was tight with room for air to get into the transfers and down for the intake port so really nothing that needed improving.
As far as the engine as a whole, I did some light cleanup porting before I sent it for plating, and I surfaced the head after I fixed the damage in the chamber to get the compression back up. Mainly I wanted to do the crank stuffing as a "Reliable" means to increase power. Increasing plain static compression on a 2-stroke drastically reduces reliability, and I wanted to be able to be on the throttle for a long while riding the ice with this one without detonation. If you haven't already I have a separate thread for this trike called '84 tecate build w/pics, I just wanted this to be a separate topic for discussion.

[El Camexican]

Those holes being rough is a surprize, thanks for the explanation. Here is a link my my attempt if you are interested. It seems to have more snap, but without a dyno or 1/4 slips to compair who knows, still its fun to experiment.
http://www.3wheelerworld.com/showthr...300exc-rebuild

[El Camexican]

Here are the only photos I can find of the crank. Nothing special, just doesn't have plugs in it.

[81Rmachine]

Very Cool thread and very nice work, I didnt realize the KTMs were case reed motors same as my CR. Glad to hear your outcome was good. I kind of wish I would've CC'd the crankcase before and after just as you mentioned especially with all of the epoxy and nylon that went into it lol
I guess we'll just see, there's only one way to find out right? Im really anxious to fire it, just have a bit more grinding on the epoxy i used to patch the previous owners hole in the clutch cover and she should be coming together within a week or two, as soon as I have an ounce of time!

[81Rmachine]

The holes on your crankshaft look like they have a much better surface finish and are much further from the rod than mine were. KTM could have very well used those as alignment holes as well. Theres alot of room there to fill.. not trying to somehow inspire you to tear apart your gorgeous bike, but it makes a guy wonder if it would be for better or for worse. See this is why I wanted to start this thread I was hoping some people who had experience with this would come outta the woodwork so thank you for sharing!

[El Camexican]

There is a guy that works at KTM World (I think Paul Wright is his name) He does stroker engines and case stuffing, etc. If you can get him on the phone for a few minutes you may get some good info. There isn't a lot of usefull information on the Internet about this as I'm sure your are realizing.

Regarding case volume here’s something to consider: My 2002 300 engine shares cases with the 250 and the 380. The only difference between the 3 engines is that the 250 has a smaller bore that the 300 and the 380 has a larger bore and a 5mm longer stroke. The cases are all identical, so when you consider that a 380 and 250 share case volume it makes you wonder how important it is to the power-band.

Please keep posting anything you learn.

PS. Nice shop!

[just ben]

Hmm I just ran across this thread by accident. I can tell you that I have an 84-85 tecate engine that has aluminum slugs in those holes. I can't tell you any difference in performance since I have not run the engine. However it was a national race engine built by JP racing and I have to think they did their homework before putting these engines in the racing circuit.

[81Rmachine]

Ben, thats pretty interesting, I wasn't aware anyone did any stuffing before dirt bikes had it done factory except for old vintage sleds I guess.
Well I just got it running here this past weekend, and I can say it did make a noticeable difference. It didn't seem to make any difference in the lower end, I can lug it and it pulls just as hard as it did before, no worse, no better, but it made a pretty positive difference on the upper end. This engine didn't exactly have a light switch powerband from the factory, It pretty much surged into the powerband like a good powervalve engine does. Now it gets up to the powerband and really hits, I like it alot, It makes it so much more exciting to ride. Its not that its peaky or all top end like alot of engines are with abrupt powerbands, it just gained enough on top that when it does hit the powerband it pulls that much harder and makes it feel more like hitting a switch.
In conclusion, I would definitely recommend it! If you have the time and the ambition go ahead and try it for yourself, I had very good results from it and had fun building the engine, It was a learning experience! I'll have to get some vids of it soon and post them if anyone is interested, Nick.

[Keith Salyer]

On our Cammex motors Calvin used cork plugs with epoxy for strength.

[barnett468]

I wasn't aware anyone did any stuffing before dirt bikes had it done factory except for old vintage sleds I guess.

2 stroke crank stuffing has been around since at least 1976.

"Turbo venting" on crankshafts has also been around that long also. A guy brought a stock crank into the shop I worked at which he had cut angled wedges out of. He was offering the process as a service for high perf builds. We passed.

[barnett468]

Hello 81Rmachine;


There's some photos of works cranks and other parts in the links below. How about a set of magnesium engine cases that weight 5 lbs, or a 1 piece clutch basket that probably weighs 1/3 of a of a production one and a shifter machined made from billet aluminum. Anyone want a hand made titanium ex pipe, Suzuki had one.

http://www.mxworksbike.com/Honda%20works%20parts.htm

http://vintageworksbikes.com/zMiscworksparts.html

[just ben]

My crank has had other work done besides being stuffed. It is also turbo veined liked Barnett mentions and the rod was lightened and polished. I have heard mixed thoughts on the veining. I believe the idea is to move more air/fuel, some say that it starves the bearing of oil.

[barnett468]

All I know about "turbo veining" for sure, is that it increases the volume of the crankcase, and that it was never used in any production or works Kawi.

My guess is, Kawai as well as the other mfg's, knew about this technology a long time ago, and would have done some testing on it if it looked good enough on paper. They may have done this, however, we never would have heard of it if it failed their tests in Japan.

Even if it did cause premature bearing failure, they certainly would have used it on the works bikes if the overall benefits in performance outweighed any potential loss in performance caused by the increased crankcase volume the process creates.

They rebuilt the engines after every weekend anyway, so as long as it lasted that long they could care less.

Kawi, as well as most of the other mfg's have a ton of money, the time and the equipment to make "turbo veined" cranks and test them.

When I was testing the 86 prototype T3 in Japan, I Told them it needed 41mm fork tubes. It had the same tubes as the 85, but with longer travel, nice.

They didn't have such a thing, yet somehow, they made the complete fork assemblies AND tripple trees in around 3 days.

Since they could perform that amazing feat, they easily could have popped out as many turbo veined cranks as fast as they wanted if needed.

Anyway, since Just Ben has one, and his bike still runs, it obviously doesn't kill the bearing off instantly.


The name certainly sounds cool at the very least anyway.