03 Wombat restoration in search of insight

[Ncholas]

I have a 1976 03 Wombat. The street legal model with the orange tank and black painted frame. The top end of the engine was torn down by my great grandfather. When I got the bike just recently it did not come with the top end that he took off I have the entire bottom end on the bike still including the oil reservoir. I am only missing the carb, air filter, piston and cylinder.

When I got the bike I also got a mostly complete motor to a 125 combat wombat. My question is since they are the same size motor would I be able to take the top end off of the combat motor and put it on the bottom end that is on the bike or will I need to switch out the entire motor just to get the bike running? Also any insight on how the separate oil reservoir ties into the motor would be greatly appreciated.

[thrownchain]

First you should verify the frame and motor numbers. Then the plan going forward would be to go thru the motor and check out it's condition. If the top end has been off for an extended period of time, you want to check for rust,and replace the seals and gaskets as well as look for parts that have damage or wear beyond normal limits. It may be a lot of work, but then you'll know the condition of the internals. And you could head off having bigger problems later. What area of the country are you in? Maybe other owners in your area that could help out.

[Bullfrog]

Nicholas,

Get set for one of those "good news, bad news" sorts of stories. First of all it is grand that you have this machine with its deep roots in your family!

. . . however . . . due to the simple passage of time (and the open crankcase too) . . . you really should "split the cases" and replace all the rubber parts which seal the engine. You just can't depend on 40 year old rubber seals to, well, seal.

By happenstance the engine you have (Model 03) has its own unique crankshaft/connecting rod/piston and rings. So while you can indeed use a Combat Wombat cylinder and head on your engine -- and it will accept the Model 03 piston (IF bore size/clearance is good), you can't replace the 03 piston with a Combat Wombat piston. You'll need to check with Hodaka Parts, Inc. about the availability of 03 pistons in various sizes. If you can't come up with the needed size of Model 03 piston/rings which are needed - there is a "plan B" which can be activated.

Plan B - get yourself a rebuildable Road Toad crankshaft assembly and have it rebuilt with a connecting rod for the Model 94/95 engine. This new "hybrid" crankshaft assembly will work in the 03 cases AND will accept the model 94/95/97 pistons . . . and can get you back on the road. NOTE: for those wondering about the "balance" of the engine after such a change - it seemed fine to me back in the 1970s when I ran a Toad crank with 125 rod in one of my ISDT Qualifier Model 03 bikes in order to be able to run a single ring (and lighter) piston.

We'll talk about the oiling system later - this message is already quite long.

Ed

[viclioce]

Looking on the HPI website, Terry does have std bore Model 03 pistons, but not sure about rings for it. Assuming your cylinder doesn’t need more than a mild honing, he would have the piston you need. If your cylinder had been bored at all, or if it’s std but needs a bore to clean it up, then you would have to talk with Terry and see what he has. Other sources might be Rich Gagnon, California Hodaka, or there is a guy I know in British Columbia. Are you missing the cylinder & head still? That is not clear from your post. If you need a cylinder and/or head, if Terry doesn’t have a used one check with Bruce Young at HodakaPartsIdaho.com Victor

[matt glascock]

Great info Captain. Can an M95 piston be drilled to function reasonably well in an 03 jug (as an unlikely Plan C)?

[Bullfrog]

Yes, but a Model 97 piston might be a better choice since it has slightly thicker piston skirts for improved reliability with the reed holes.
Ed

[matt glascock]

Good call. Thanks Captain. I wish I had a case of those. Hey, its a viable option now.

[Ncholas]

So what I have gotten is that I can use the cylinder and head of the cw but not the piston because the designs are different and the wrist pin is in a different orientation the the earlier models is that correct? The piston that is in the cw has been modified with reed holes and is an exact fit for the perspective jug. how would the difference in wrist pin holes affect the performance of the engine if I were to use it. I unless the wrist pin orientation was moved off of the original mark by more than the radius of the wrist pin there shouldn't be any scraping just low clearance for the skirts and rod correct?

[viclioce]

Wait. So IF rebuilding a Model 03 motor, the Model 97 piston is interchangeable??? Please say yes!!!!

Wow only $189 for a piston kit to redo a motor I bought for $80.00!!! Plus, gaskets, bottom end rebuild kit, boring, and I already bought the toaster oven! Victor

[olddogs]

Slow down fellows. The bore of both the 03 Wombat and Combat Wombat are the same at 56mm, but the connecting rod of the 03 is a different length. That's why the pin height is different. I cant remember if using the cw piston will cause it to come up short in its stroke, or hit the head. The difference is great enough that no home modifications are possible. Swapping the rod is the common approach for switching to the more available SC or CW pistons.

[bobwhitman]

And note that the conversion Ed discussed requires using the RT crank as well as the rod. 03 crank, rod & piston are a unique combination; you must use all three or none!
Bob

[dirty_rat]

I have always wondered why you couldn't just replace the 03 rod with a 94/95/97 rod. Is the bearing a different diameter or the rod a different thickness at the lower bearing, or something like that? I know they both had a 50mm stroke so the bottom end pin should be the same distance out. I don't need to do one, just wanted to know for my education.

Thanks

[Bullfrog]

Sorry folks, I don't have time to dig out the dimensions for WHY there is only ONE way to use model 94/95/97 pistons in the model 03 - but that IS the way it is. Please go back up the thread and re-read my post which mentions "Plan B".

- you can NOT run a model 94/95/97 piston on a Model 03 connecting rod
- you can NOT run a model 94/95/97 connecting rod on a Model 03 crankshaft
- you can NOT run a model 94/95/97 crank shaft assembly in the Model 03 engine (crank assembly will not accept primary kick start components)

The Road Toad/painted tank Dirt Squirt (models 99, 01 & 02) crankshaft assembly 1) will accept the primary kick start components and 2) it can be re-built to have the 125cc rod for models 94/95/97 which will then 3) accept the model 94/95/97 pistons . . . and ALL of that can go into a Model 03 engine.
Ed

[viclioce]

Thanks for the great clarification Captain! That laid it out explicitly! Victor