Model 97 - Finally getting started

[matt glascock]

Hi Geary, Based on the 99%/1% usage ratio you stated earlier, I would go for longevity, lower maintenance, and reliability. The closer you get to maximizing output, the harder you have to work to keep it there. More riding + less rebuilding = most fun.

[Bullfrog]

Even without the 99 to 1 useage ratio mentioned earlier, I'd recommend the 03 cylinder. You would be amazed at how well that engine "pulls" with a good pipe on it. (and you don't have to be a clutch fanning master if you get a bit down on the "R's" coming out of a corner.) That 03 cylinder is SWEET for a multi-purpose engine!
Ed
PS: Please don't port an 03 cylinder to become a Super Combat - you can't go back . . . and a great cylinder will have been "used up" in the process. (My 2 cents.)

[viclioce]

Are the SC & the 03 barrels the same length? Are the intake & exhaust ports the same distance up from the bottom? I would guess they they would not be if the 03 and 97 pistons can’t be used on the other’s rod? Are there differences in the piston domes?

I’d stick with the 97 cylinder if you can. No sense in throwing anything difficult into the mix if that possibility is there. Victor

[gearyoliver]

Ed, I had a blast riding the 03 I rebuilt last spring. Been a long time since I rode a 125 and I was surprised by how it pulled me around. I am hoping to save the 03 cylinder for a CW project down the road. Since I've never ridden a SC and don't know what to expect, I want to figure what if any mods are likely to make it even more fun to ride.

Vic, It's always possible and usually probable for me to make things more difficult . And I have most or all the parts to do so. LOL!

[Bullfrog]

Vic, the 03 cylinder will "bolt on" any Hodaka 125. You could remove the head and cylinder from a Super Combat and replace it with the 03 cylinder and head - using the exact same piston if the two cylinders were the same bore size (std, 010" over, etc.)

The exhaust ports ARE different heights (usually measured from the head gasket deck). That difference in exhaust port height is precisely why the two cylinders have different hp/torque curves.

As for the intake ports (comparing SC to 03) -- it sort of, kind of doesn't matter how they may differ because both are reed induction. So "intake port timing" is not really important. This is because the reed valve is in control. When the air pressure below the piston rings is lower than ambient air pressure at the carb -- air/fuel mix WILL flow into the engine. When the air pressure below the piston rings is higher than the ambient air pressure at the carb -- air/fuel mix will NOT flow into the engine AND due to the reeds being closed, air/fuel mix will NOT flow backwards toward the carb. Nifty!

Ed

[viclioce]

Well! That’s interesting that you can swap out cylinders but not pistons! Can you use the SC piston with the 03 cylinder, or do you have to change to an 03 piston? Some of this stuff about what will swap out & what will not is quite confusing to me still! If one has a different rod than the other, it made me think the pistons won’t line up with the ports correctly or that the top of the piston with a SC piston wouldn’t reach high enough to give correct compression, with an 03 cylinder. Why isn’t that true? I appreciate the explanations for the education! Just curious. Victor

[Bullfrog]

Re-read the previous message. Then oll the SC into the middle of the shop. Remove the cylinder and head. Now install the 03 cylinder and 03 head on the SC engine in that bike. It is a bolt on. (we are assuming both cylinders are, let's say, .020" over-size. We are overlooking proper piston to cylinder clearance issues.) But the cylinder AND head swap IS a direct bolt on. The end.

NOTE: I did not mention swapping pistons. They can't be swapped. But it doesn't matter. (See above paragraph.)

Ed

[gearyoliver]

Here's some poor art work to show the difference between 94/95/97 and 03 rods and pistons.
At least as I understand it.

Note: I dont know which has the higher pin height, it's late and cold and I don't want to go outside and look.

Since the stroke is the same the overall piston height is the same. However if you mix up the piston and rod you either have too much overall height or too little. The first might push the piston crown out of the cylinder. The second might not turn over if the piston skirt contacted the crank wheel. Again I don't know without measuring but both are bad...very bad.

[swcaudill]

The piston on the left is the 03. The distance from the top edge of piston to center of wristpin is 35.5 mm.
Sterling

[matt glascock]

Good clarifications (and artwork), fellas.

[viclioce]

Nice drawings! I didn’t know the difference in the rod length was offset by a change in the wrist pin location on the piston! Now it all makes Chrystal Clear sense to me! The drawings were a great idea!!!

I’m still trying to get my 03 cylinder off the cases. Piston is stuck to the cylinder. I sprayed it with PB Blaster and left it to penetrate. I’m hoping with the time it’s had to sit that it will come free with some tapping from a rubber mallet. Once freed, I’ll send it to Terry and see if it can just be honed and a Std piston & rings fitted back in. He at least still has Std Model 03 pistons.

I’ll have Terry send me a Model 03 bottom end rebuild kit and a HD kick shaft retainer bearing, & I’ll rebuild the bottom end while Hodaka Dave cleans up the cylinder.

Once the cylinder is removed, I will take the inner & outer cases, cylinder & head to be vapor blasted. I found a guy about 38 miles south of me who does it. Larry did a wonderful job with my CW vapor blast, but I think I paid more for packing & shipping to Larry than it will cost me to put the parts in a box, drive down and have the blasting done locally. I’ll post before & after pics when I get it done! Victor

[gearyoliver]

Progress.

[Bruce Young]

Ed, is the 03 cases compatible with any other models cases or inside parts. I understand the Cyl., switches over to other models but what about the trans, crank and etc crossing over. Bruce

[dcooke007]

03 engine is a totally different animal. Crank, cases gears MOST parts not inter-changeable with other models. The 03 cylinder head gets very little respect but the combustion chamber shape / lay out is prefered...at least by me.

Danny

[gearyoliver]

Bottom end assembly day!

[gearyoliver]

BTW... In for a penny in for a pound

And no Ed I didn't use my 03 cylinder

[gearyoliver]

The fenders are about the only pieces on the whole bike that are useable with just a little cleaning.

[viclioce]

You can use some wet/dry 1000, 1500 & 2000 grit to make them smoother again. Just use plenty of water. Victor

[gearyoliver]

Closer

[gearyoliver]

Fitted 1990 RM250 air filter and cage. Mounted Honda cdi unit. Test fit engine. Next is finish up clutch and pressure test.

[bobwhitman]

Geary
Is the RM filter & cage switch suitable for a simple Resonator article?
Bob

[gearyoliver]

Bob,
It would be if I was the one with the idea. Credit goes to Kelly and Greg, they put a great write-up in issue 2-24. I used an RM unit cause it was handy.

[gearyoliver]

Pressure test fail. JB Weld to the rescue.

[gearyoliver]

Can't post picture at the moment. Found a pinhole near the stator mount bolt hole. Try again after it dries.

[gearyoliver]

Pinhole