I recently put together this franken-quad from two chinese atv's. One had an excellent frame and suspension but had engine issues, the other had frame and bearing issues, but a sound engine (or so I thought).

After the build, the engine fired up without any problem at all. It seemed to run fine. I took it out this past weekend for a test run. The initial phase of the test run seemed to go ok. Once I reached the end of the trail to head back, it died and refused to start. I could occasionally get a slight pop of ignition, but nothing to really get the engine going.

I was sure something was clogging the carb, as the place I was in was very sandy, and it looked like the boot has slipped off the back of the carb just a bit. A thorough carb clean yielded no results, as did a new plug.

For s's and g's, I placed my finger over the spark plug hole while trying to start. It wasn't even enough compression to generate a lil squeak through my finger. I got the quad back and performed a compression test. Sure enough, this thing barely registered. How could I go from running, to nada compression?

I thought maybe a valve keeper screw backed off, and a valve was either not opening, or was stuck open. I pulled the valve cover off to find that both keepers were intact. I spun then engine over a few rotations to watch the valves work. The intake valve is barely moving at all. I also notice that at times, I can push the push rod down back away from the valve, and get almost a full inch clearance from the rocker to the valve spring. I cannot do this on the exhaust side.

I am about to start tearing this engine down, but I have not run into any of these pushrod chinese engines. What could cause the intake valve to not even open? From what I can tell, its not getting the demand to open like you would traditionally get from a cam lobe. Even though these engines dont have timing chains, Im assuming they would still have to have a cam? How else are the valves to be engaged? Im at a loss here. Ive also looked around the net and have had no luck finding an engine diagram or service manual. This is the "GC200" style engine, vertical air cooled type.

Any insight on the probable cause of this issue would be greatly appreciated.

 

D'oh! Make that a "CG 200" engine style. I have a 250 cc version of the same type sitting in the garage with a blown bottom end. After looking at some of the parts listings, it looks like the 250 cylinder may match up to the 200cc bottom end. Anyone done this?

 

to be honest, i don't have a spec book on that style engine. all i refer to is this website and give these folks a call. they might have a manual..

Cg 200cc Engine Parts - By Engine Size - Cg200 Engine Gaskets Stator Cover Gasket - Clutch Cover

i've never had to franken a motor together. heck if it looks like they'll mate up, why not try it? i do know that roketa has made an expansion kit for their 150cc to make it a 200cc w/obviously more hp at the ground.

 

Luckily I had the spare 250cc engine of the same style, so I could just break it down piece by piece to see how it was laid out before doing anything on the 200cc engine.

This morning I decided to go ahead and pull the head and valve assembly off. And just before I did, I happened to look across the top of the valve springs, and notice that the intake valve was sitting much lower than the exhaust. It somewhat confirmed my suspicion that the intake valve was stuck open somehow, I just didnt know why.

A few bolts removed, popped off the head, and this is what I find...




WTH!? Yeah, that will cause a compression loss! Then it dons on me. When I was removing the carb to better fabricate the air hose, I dropped a carb nut and couldnt find it. I looked all over the place for this nut. I even slid a finger up into the intake to feel for it. I finally assumed it just rolled under the tire of one of the other ATVs, and I just used another nut that fit.

Luckily the nut didnt fall into the cylinder and cause some serious problems. Now I just have to make sure the valve wasnt damaged. I plan do clean off the surface and fill it up with pool of oil to see if any of it seeps through.

Other than that, if my seal test is good, I plan to just put the engine back together and fire it up. Does anyone have torque settings for these head bolts, rocker assembly bolts, etc? Im not sure if I will have to replace these gaskets since I broke the seal, but I planned to get it all together and perform a compression test to see if I'm all good.

 

wow, i wish you the best of luck on this repair. it appears from your pics the valve will be fine, thank goodness the nut is a "cheap/soft" metal. we had a post here while back about the torque settings, but i can't find it. i'll PM you some advice.

 

Much appreciated Jaster. On the subject of the top end conversion from the 200cc to the 250cc top end, Im still a bit unsure. I mic'd the bolt pattern and it matches perfectly. However, something donned on me the other day regarding the stroke of the engine. I was sure the stroke of the 250 would be slightly longer than that of the 200. Sure enough, I mic'd the cylinder length, and found the 250 cylinder to be slightly taller. I dont recall how much taller, but I seem to recall the difference to be in the neighborhood of 2 to 3mm. I am not sure if this is enough to make a difference, but it was clearly taller on the 250.

I can speculate that the shorter stroke on the 200 will cause the 250 top end to have an even larger displacement due to the crank not pushing the piston as far up the cylinder.

Do you (or anyone reading) think I may just be splitting hairs here, and that it should bolt up and work? I still have the carb to the 250, so I would imagine I would need that larger main and pilot jet size to deliver the necessary fuel. The exhaust systems seem almost identical, just a bit more length on the 250.

If I had access to a machine shop, I suppose I could get someone to shave the cylinder down enough to match the 200, then be able to have a nice short stroking 250.

 

I have a redcat 200cc water cooled engine and it's blowing oil out of the case vent tube. I'm suspecting a broken piston and or ring, but I would like to know what the compression psi should be for this engine. thank you.

 

should be > 95 psig.

 

Thank you very much. Do you know a good place to buy parts or a complete engine ?

 

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give them a call to chit chat with them. you might be better off going to the air cooled system rather than the water cooler. just a thought.