This Combat Wombat engine was sent to me dis-assembled a few weeks ago from Phil LaChapelle. Phil has had this bike for a while and decided it was time to get it going again.
Measured the piston rod side clearance and found it to be excessive at greater than .020 inch. The crank pin was worn and the outside edges of the rod bore was worn excessively on both outside edges due to the excessive rod side clearance.
The right crank bearing flange was broken off and the bore was cracked. Had to sort through my spare parts and find a usable set of cases.
Cylinder head was incorrect and from a Wombat so had to search my spare parts. Came up with a Super Combat head that will work for this build. Pictured is the Wombat head.
Shift cover parts were worn excessively.
After finding usable parts, cleaning and coating this is were I ended up at today.
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dcooke007 - 03/15/12 at 9:38pm
Got a little more accomplished today.
Polished combustion chamber on replacement head to shed carbon.
Started working on the clutch cage and attempted to true up the splines that engage the clutch steels. This is usually appropriate but too much wear has occurred. In the last picture you can see the excess clearence as well as just small point contact between the steel and spline....hard to show well in the photo. Any way time for a new clutch cage.
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dcooke007- 04/01/12 at 12:59am
Started assembling and adjusting the shift cover today. After all the discussion about shifter springs I wanted a visual of the parts assembled / adjusted and the pictures below demonstrate my methods.
I decided it would be preferable to assemble the shift control shaft, o ring, springs and ball receiver to the counter shaft now so I could function check for proper operation and make sure there was no binding of the assembled parts.
Worn shifter parts replaced, coated and ready for assembly.
To observe the shifter operation...install the counter shaft assembly, countershaft spacer, sprocket collar, countershaft sprocket and nut in the left center case and tighten firmly. Install the assembled shift cover and inner shield. Now you can see how things work and verify your shifter arm adjustment.
To check and adjust the shifter guide side clearence you will have to bolt the center cases together with a few screws and bolt on the shift cover. There should be no side pressure between the control shaft and shifter sliding pin. This adjustment is made by selecting the proper spacer / shim.
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thirdstone - 04/01/12 at 6:54am
Danny Not sure why you need to bolt the center cases together ?
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dcooke007 - 04/01/12 at 1:20pm
Kev, The countershaft can move when only supported by one bearing. The shaft doesnt move length wise but if you grab the right end of the countershaft it will move side to side allowing the shifter sliding pin to move in and out of the control shaft groove. You just cannot tell how the control shaft and shifter sliding pin fit that way. The countershaft has to be supported on both ends for this check. There must be some clearance between the two parts so there is no side pressure on the control shaft.
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warhatchet - 04/01/12 at 3:17pm
Hello Danny, I appreciate you sharing the CW engine information. On one of the other threads you showed drilling holes through the older clutch covers using the later model as a guide. I did not know there was a difference till then. I bought a later model cover and drilled a couple of covers and it worked out perfect! Thanks! I going to do everything I can to make these clutches last longer. Ok...I see a hole drilled through the top of the shifter cover. I am guessing this is for a vent fitting? Richard
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dcooke007 - 04/01/12 at 3:26pm
Hello Richard, The hole is drilled and threaded....it was that way when received from the owner. He has a fitting that will be installed and a vent hose attached. I have never used a vent before and not sure about it usefulness. Maybe some one can shed some light on this modification and its intended purpose. I would assume it is to allow air flow and would help to prevent moisture build up in the cover...but this is only a guess.
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junker2k - 04/03/12 at 1:52am
The thought back then, was that a very high RPM motor (flat tracker) could build up pressure in the cases and blow the gaskets out. This could oil down the track and send you to the pits. This could really only happen if the original breather was some what plugged. I will bet very few people have ever checked the vent. The best way I found to vent the cases was to pull out the original breather (under the carb) and drill a hole straight down down in it. Put it back in then hook a hose to it and run it up under the tank.
Jack K
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Bullfrog - 04/03/12 at 2:06am
Jack, I think you are talking about a different vent than the question was about. Installing a vent for the shift cover (magneto area) was done to make sure that pressure changes in that volume didn't suck water through the seam between the shift cover and the center case.
It was always difficult to fully seal the magneto volume what with the requirement to seal the aluminum shift cover to the steel inner cover AND seal the steel inner cover to the center case. So even if you were successful at sealing things up . . . when the engine came up to full temp, the air in there got hot and tried to "blow its way out" -- usually successfully at some point in time. And then, you'd come to a long creek crossing and the cold water would cool down the shifter case (and the air inside) which lowers the pressure inside the case at the exact time that the full perimeter of the seal is covered with water . . . so water and grunge gets sucked into the case. Sooner or later, moisture or grunge would cause problems with the points.
A vent allows that hot or cold air to move thru a vent tube which was usually routed up over the lower backbone tube under the tank, with the end pointed down -- and with a light "breathable plug" of oiled air cleaner foam inserted in the end of the tubing.
-Ed
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dcooke007 - 04/08/12 at 10:21pm
I hope every one had a happy Easter. After church and family activities I was able to complete some more work today.
Assembled and trued the crank...used one of Paul's rod kits and found it to be first class in every way.
Be sure to clean out and chase all the threaded holes...I never seem to be able to get all the blasting debris and gunk out any other way. After chasing flush out with spray automotive brake cleaner.
This is the product I use to seal the center cases. It is made to seal close fitting machined surfaces. This product is resistant to fuel, oil and only the portion trapped between the cases cures. Tomorrow I will dampen a cloth with spray carb cleaner and clean off the excess. This product can usually be purchased at most auto parts stores. this product seperates the same as any other case sealer. I have used it alot in my full time job as an auto mechanic. During my time at Chrysler Corp dealers this product was developed to seal transmission cases with machined flanges. Last year I had to repair my 120 hp, four cylinder two stroke outboard engine and this is the specified sealer for those engine cases. As for clean up...the sealer leaves a thin film that I remove with spray carb cleaner and a new razor blade held at 90 degrees to the sealed surface. The carb cleaner loosens the bond and the razor held at 90 degrees acts as an effective scraper. Although the Permatex tube looks like blue loctite it is not the same product. This is Permatex Anaerobic Gasket Maker. Blue loctite is a medium strength fastener locking compound and would not work as a case sealant.
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dcooke007 - 04/09/12 at 10:47pm
A little further along after work today. Received a new clutch kit and cage from Paul so assembly of the clutch can be completed.
I see too many clutches not properly safety wired. The arrows by the screw ends indicate direction of tightening. The safety wiring is to be done in such a way as to pull the screw in a tightening direction
Also I have seen where the tag end of the safety wire is attempted in the middle of two screws...this would not be proper also. Best to terminate the safety wiring at a screw as demonstrated. There are also some self locking nuts that can be used rather than the safety wire. I like safety wire myself.
Before installing the spiral pin I prick punch the hole to displace a little metal to tighten the fit and assure it does not come out.
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dcooke007 - 04/10/12 at 11:56pm
This was my day off so I spent some more time on the engine. Phil had the cylinder bored .030 before sending it to me except the ports had not been chamfered. I used a sharp three sided scraper for this task. Piston crown was polished to shed carbon. Piston pin was a firm thumb push fit to the piston pin bore so no fitting was required. The surface rust in the bore is from the cleaning and coating process as no oil can be on the parts during refinishing.
Knife edged the intake bridge and matched the intake port and intake manifold opening.
Semi polished the exhaust port to improve flow and also to shed carbon. No changes were made to the port timing or shape.
Squared up the piston ring in the bore with the piston and checked ring end gap. End gap should be checked in the range that it travels the bore...that would be from the top of the cylinder to just past the bottom of the exhaust port.
Cylinder installed after prep work and light hone.
Phil is using Paul's electronic ignition. I could not proceed any further today since I left my dial indicator at work and it is required to locate the ignition rotor and time the engine. I also still have to pressure test the engine. Carb will have to come off at that time...could not resist attaching it.
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timcc001 - 04/16/12 at 10:22pm
Hi Danny,
Tremendous attention to detail. I wish this build thread appeared two years ago when we were working on our "E" engine Dirt Squirt.
Would you be so kind as to explain the purpose of chamfering the port edges ?
Thank you,
Tim
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dcooke007 - 04/16/12 at 11:03pm
Hello Tim,
The tops and bottoms of the ports are chamfered to keep the piston ring from catching on an other wise sharp port edge / opening. The chamfer guides the ring across the port edge with out causing damage to the ring.
Danny Cooke
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dcooke007 - 04/17/12 at 11:02pm
Ok Kev here are some photos of my home made pressure tester and process.
My pressure tester consists of a compact bicycle tire pump, surgical tubing, 0-15 pressure gage with 1/4 npt thread, female 1/4 npt thread brass pipe tee, two 1/4 brass tube fittings with 1/4 npt thread, check valve and modified high pressure truck tire valve stem. The two block off plates are made of 1/4 inch thick Lexan and a thin sheet of rubber is glued to both. Lexan is not the best material to make the block off plates from and will be re-made later in aluminum. Lexan is not very resistant to most shop chemicals and is not stiff enough to provide a good seal. A small bead of rtv sealant has to be applied between the plate and the port to achieve a good seal when testing. The fitting screwed in the lexan intake plate is 1/4 brass tube fitting with 1/8 npt thread.
This is the modified high pressure tire valve. The valve stem core has been removed and the rubber part of the valve stem has been removed leaving the brass tube that works well with the bicycle pump and surgical tubing.
This is the check valve is to maintain pressure in the cylinder ...this and all the brass fittings and high pressure valve stem were purchased at my local auto parts store.
With 6-8 psi pressure I noted the gage would not hold stable pressure. Using a mixture of dish washing liquid and water the leak was found. Removed the head, lapped reinstalled and no more leaks
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dirty_rat - 04/19/12 at 12:14am
Instead of a bike pump and check valve, I got one of the squeeze bulbs from a blood pressure cuff. It has a built in check valve and it is easy to regulate the pressure ( so as not to overpressurize ). You can also release the pressure by turning the knob on the end of the squeeze bulb. Just another idea from those out there wanting to make a pressure checker. I found my squeeze bulb on e-bay, under blood pressure testers. It was about $5, with shipping. I agree, on a leaky engine, a foot pump would be handy
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dcooke007 - 04/19/12 at 11:02am
The squeeze bulb does work also. I had no trouble controlling the pressure with the tire pump. In hind sight I would consider a foot controlled tire pump. That way if I had a very leaky engine I could continue to operate the pump while looking for the leak at the same time.
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thirdstone - 04/19/12 at 6:22pm
Thanks for the posting, There are some good idea's for pressure delivery here. I am using just a normal compressor Tyre pump and you are right in that you need to be very careful not to over pressurize with it.I did buy a leak down tester that has a regulator on it but i found it was not sensitive enough for very small leaks,say 2psi and under a min. What it is good for is big leaks because it supplies constant pressure allowing you time to find the leak but having said that a big leak is pretty easy to find. The foot pump would be ideal. A tip I have followed from my bearing shop was to put a thin layer of gasket goo on the outside of the case seals , they still come out easy enough.
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dcooke007 - 04/20/12 at 9:18pm
Installed the ignition rotor, timed the engine and completed assembly. Only have to run the engine and then ship to owner.
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MWL - 04/21/12 at 6:54pm
Danny
What size (dia) safety wire do you use on the clutch ?
Mike
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dcooke007 - 04/21/12 at 10:36pm
Mike, I bought my safety wire some time ago and it is .032 inch diameter. It came in a one pound plastic can.
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dcooke007 - 04/24/12 at 9:45pm
No pictures to post today but installed the engine in a roller frame and started. Started 2cd kick and did not want to idle quite right. Would idle ok with the air screw turned all the way in. Removed the carb and checked the pilot jet which was a #25. No blockage noted, sprayed carb cleaner through passages in case there was something I did not see. Re-installed carb and same thing..would not idle properly unless air screw turned all the way in. Removed carb and installed #30 pilot jet and now idlled properly with air screw turned out 3/4 turn.
Started the engine and allowed to come up to operating temp and allowed to cool. Did that a couple of times. After that decided I should check compression and got a surprise. Compression was 190 to 200 psi....TOO MUCH COMPRESSION. So it seems the Super Combat head should not be used with a Combat Wombat cylinder unless you want that kind of pressure. For this engine and the way the owner will be using it that is too much pressure. Found a Combat Wombat head in my attic so I will have to refinish it and install.
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dcooke007 - 04/27/12 at 12:01am
Well if you read my last post you know the cranking pressure the engine produced was more than desired. So today I decided to prep another head and take some measurements. Although initially Phil's head did not appear to be a Combat Wombat, a second look confirmed it was. There were some pock marks in the combustion chamber from a broken ring, failed bearing, etc.. I smoothed the pock marks, polished the combustion chamber and lapped the head gasket surface. Refinishing still needs to be performed.
I decided to cc the Super Combat head and the Combat Wombat head. The Super Combat measured 11 cc's and the Combat Wombat measured 14 cc's. So, with these two heads, this particular Combat Wombat head has a larger volume of 3 cc's which will lower the cranking pressure / compression. The picture shows the Combat Wombat head with spark plug installed, plexi glass plate with hole in center and a thin layer of grease used to seal the plexi glass. A burette is used to fill the cylinder head and measure volume. I used plain water to fill the combustion chamber. Some food color could be added to see the liquid better but I used what I had on hand at the time. Alcohol, not the drinking kind,
with food color would be a good liquid to use also.
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Forum Admin - 04/27/12 at 8:59am
Danny as always a great job explaining things with great photos to back it up.Your input and thoughts are very welcomed!
I had thought the CC's for the Super Combat head were 11.2 I know this is splitting hairs but IF someone plays with modifying their head this might be helpful. I do not mean to correct you but rather just put this out for discussion.
Great talking to you the other day !
Thank you
Paul
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thirdstone - 04/27/12 at 9:04am
Hi Danny, how have you reduced the compression?
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Forum Admin - 04/27/12 at 10:06am
Kev by adding more cc's to the combustion chamber.
Paul
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Bullfrog - 04/27/12 at 10:32am
Or, more simply stated - by removing the wrong head and installing the correct head.
Ed
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thirdstone - 04/27/12 at 7:06pm
The way I read Dannys post was at first he thought he had the wrong head but then confirmed by cc'ing that he did have the correct wombat head. So I was wondering how he corrected the compression that's all. The only way I know is to add a thicker head gasket or get the dome machined.
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Bullfrog - 04/27/12 at 8:07pm
The post on Apr 24 @9:45 makes it pretty clear that a Super Combat head was installed on the CW engine . . . and the result was wayeeee too much compression.
Ed
(there was problem identifying exactly which head was supplied with the engine for the re-build . . . but it turned out it was the correct CW head)
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dcooke007 - 04/27/12 at 9:04pm
Kev, Ed and Paul are correct in their comments. Even if sometimes things do not turn out as expected, as in the cylinder head issue, I like to post the information discovered so others can learn also.
I was really surprised to see how much pressure the Super Combat head produced when combined with a Combat Wombat cylinder. 3 cc's is not a lot.
Paul, I wonder if .2 cc's would make much difference. My burette is only graduated in one cc increments. Good information to know though and I also enjoyed talking with you.
Danny Cooke
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dcooke007 - 05/02/12 at 11:11pm
Re-finished the Combat Wombat head today, installed and pressure checked engine again with no leaks....will install in roller frame and check cranking pressure. Will report results when completed.
The PVL electronic ignition instructions listed several warnings to make sure the engine was properly grounded. Failure to do so could result in failure of the system. This is an expensive ignition system and it would be short sighted not to heed their warnings. I took some ohm meter readings and found out the engine coating I use is an insulator and will not conduct electricity. Before installing the new ignition stator I scraped the coating from the mounting points. Also I know that sometimes engine mount bolts loosen and that would result in poor / intermitant grounds. With that in mind I decided to make and install a seperate 10 gage ground wire. The ignition stator bolts to the left inner engine case so I supplied the ground to the left inner case as pictured. The ground screw location is back far enough that it does not pierce the magneto area. The other end of the wire is attached to a hole drilled in the engine mount after all paint is removed. Paul also supplies a seperate ground that goes to the cylinder head and that will be installed on the Combat head. The thinking behind all this is to supply as direct a ground as possible.
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thirdstone - 05/03/12 at 12:20am
Thanks for posting Danny. Just thinking that you could have bolted that lead to a hole drilled in a head fin and do away with the clip-on lead at the same time.
Kev
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dcooke007 - 05/03/12 at 11:03pm
Kev, I really wanted to eliminate any concern with the engine ground and that is why I decided to ground the engine, frame and ignition as I have. Left engine case to frame, cylinder head to frame and ignition components to frame. Pictures attached.
Installed the engine in my roller frame, started engine and ran until operating temp was reached. Removed the spark plug and with the Combat Wombat head I ended up with 160 psi cranking pressure which is more in line with what I was aiming for. At this point the engine will be removed, cleaned and shipped back to Phil.
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Forum Admin - 05/04/12 at 7:34am
Danny great information. I need to ask though when you checked compression was the engine cold ?? This would make a big difference also if the rings had not been seated by the bike running for about 30 minutes did you spray a shot of WD-40 or something else in the spark plug hole?
Thank you
Paul
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dcooke007 - 05/04/12 at 10:41am
Paul, the engine compression was checked when it was at operating temperature. Also the engine has gone through several heat and cool down cycles. The engine has been operated for at least an hour and I am sure the rings have seated by now. I use a small container to supply fuel to the engine.
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Ron - 05/04/12 at 10:46am
Danny,
Did you use a stock thickness copper head gasket?
Thanks, Ron
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dcooke007 - 05/04/12 at 10:53am
Ron, I used the stock aluminum head gasket. Phil had purchased a gasket set and shipped it with the engine.
Danny
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dcooke007 - 05/13/12 at 10:34pm
Phil installed the engine, replaced the brake shoes and test rode the bike today. Below are some pictures for you.
Danny Cooke
Ps, this bike has been sitting for a number of years...nice to see it mobile again.
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dcooke007 - 06/25/12 at 12:57am
Phill sent some helmet cam video of his Combat Wombat and they are really cool. Links below, enjoy.
Danny Cooke
https://www.dropbox.com/s/6ta8yyezlu3uaqi/GOPR0086.MP4
https://www.dropbox.com/s/lrk4jbabr8n0xl1/GOPR0087.MP4
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JimKlaas - 06/29/12 at 12:18am
Danny,
Great information. You should teach a class! I am about to "try" and rebuild a Road Toad Engine. I suspect they come apart a lot easier than they go together. I am going to go slowly and keep referring back to your posts. What process do you use to blast your cases etc?
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dcooke007 - 06/29/12 at 4:11am
Jim, after degreasing the parts I abrasive blast them with 120 grit aluminum oxide. That is the recommended process for the Gunkote finish I apply. Let me know if you need any help with your build...always glad to help out.
Danny
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END OF THREAD