oil pump chain cn250

[rv. chuck]

i have a roketa gk13 torn down for a blowed had gasket i also found a damaged piston and one timing chain guide was warped pretty bad.

i discovered the oil pump is chain driven and then i noticed the chain has alot of slack in it. i it normal or does the chain need to be replaced? the cog is good i didnt notice any damage to it what i considered normal wear around the teeth no broken or missing teeth in fact the engine looks new on the inside except for the mentioned parts. the chain doesnt look stretched i didnt find any missing pins either.


id like to order some parts but this is holding me back.

[sargentargent]

The oil pump chain looks very loose to me. I have a GK-06. Some slack is ok but that chain seems to be stretched out quite a bit. I'd replace it, the oil pump and check the water pump components for binding. Something is putting a big load on that chain. I would replace the crankshaft and piston as well since you are tearing the motor down anyway. If you have an old variator, clutch and belt I'd replace those as well. Also check for binding in the transmission with the cart lifted off the ground and the clutch off. Try turning the shaft by hand to see if anything is locking up. Make sure your flywheel overrunning clutch (attached to Flywheel with 3 Allen Screws and is installed into the large starter gear) is working properly (gear should only move in one direction and lock up in the other direction) and check for metal in the crankcase as the piston is damaged. Clean it out as best as you can. After you replace the crankshaft and piston and gaskets make sure you set the timing properly. On my GK-06 there is a line next to the 'T' stamped into the Flywheel. Make sure the piston is at Top Dead Center and that the line on the Flywheel is in the middle of the cylinder body (the woodruff key that fits into the front of the crankshaft must be installed for this step) and install the camshaft with the hole in the camshaft sprocket at the top and the lines scribed into it parallel to the cylinder head. Then Install the rear cam bearing holder. Tighten all the cap nuts with the copper washers (the ones that go on the studs) in place in an alternating pattern. Don't forget to put the lower cylinder body bolts (if applicable) back in and tighten them. After this you can install the valve cover (I assume your rocker arms are in the valve cover...right?) and loosen the bolts that hold the moveable retainers in place. Move them away from one another until you feel a little resistance and back them off 1 notch or graduation and retighten the bolts. Do not move the crankshaft until you have properly set the rocker arms. You will have to have the chain tensioner removed to perform these steps as well as the Flywheel (check woodruff key) until you are ready to set the timing. Do not forget to install the timing chain guides. If your engine has a black pin and spring that is pushed into the crankshaft on the front (Flywheel side) make sure you reinstall it and make sure there is a roll pin in the hole in the crankshaft for it to be inserted into. This pin is responsible for proper oiling of the crankshaft and cannot be omitted. This is a simple process for anyone who is mechanically inclined or has built automotive engines. If you have any doubts search for the manual for your particular engine. Looks like a CN250 from what I can see. Make sure you reinstall everything exactly the way it came out and make sure there is no binding when you turn the crankshaft by hand. Put oil on the piston and into the cylinder body and make sure you install the piston rings correctly. The narrow rings go on the bottom sandwiching the squiggly oil ring and the wider rings go in the second and first grooves. The piston should have an 'IN' or other marking on it. This must face the front of the engine. The top 2 piston rings should also have a marking and the marking must face up. Since your piston is damaged I would also replace the cylinder as well. The timing chain must be placed through the cylinder body and cylinder head (you can use a plastic tie to make it a little easier). If you are not confident about your ability to perform these steps I would consider purchasing a complete engine and installing it. There is no guarantee that the engine will perform properly after the rebuild as there may be other problems we have not discussed. Do not start the engine until you have put in fresh oil and listen for ANY unusual sounds. If you hear any unusual sounds stop the engine immediately and recheck your work. One more thing...The Crankshaft goes into the left side crankcase (the longer one) First and then you can put the center crankcase on and tighten the bolts on the longer crankcase side. Make sure the 2 crankcase halves are completely seated before tightening the bolts. Don't forget to reinstall the large starter gear and the smaller compound gear in that order before reinstalling the woodruff key and the Flywheel. The torque for the flywheel nut is about 75lbs/ft according to CFMOTO. Check your cylinder head and valves for damage. There is also a small 3 pronged metal retainer on my engine that holds the larger starter clutch gear in place and attaches to the crankcase with a bolt. Don't forget about it. The information I have provided is for my specific engine. Your engine may differ in some ways which is why I suggest you locate and study the manual before you do anything. The Oil Pipe must be installed after you reinstall the front cover and you must have the water pump cover off so you can align it with the oil pump pin. Also do not forget the shaft that holds in the compound gear that connects the starter to the starter clutch gear. The oil pipe uses 3 bolts with copper washers. The black one goes on top with 2 round copper washers into the valve cover, the silver one goes in the center of the engine just above the front cover and has one unusually shaped copper washer that goes against the crankcase and one round copper washer. The last bolt goes on the bottom front of the engine and uses 2 copper washers as well. All these copper washers go on both sides of the round hole in the oil pipe. I take no responsibility for any breakage or other malfunction you may encounter as a result of following these guidelines. Good luck.

[sargentargent]

Valve Adjustment:
Remove the left crankcase cover (page 8-3).
Rotate the drive pulley counterclockwise and align the "T"
mark on the camshaft with the index mark on the cylinder head
cover to bring the piston to TDC Dead Center) on the
compression stroke.
Loosen the valve adjuster lock bolts, which are located on the
left side of the cylinder head.
Move the intake and exhaust adjusters outward (away from
each other fully until resistance is felt.
Then move them inward (toward each other) one graduation.
Tighten the lock bolts.
NOTE
• One graduation on the adjusters equals 0.10 mm (0.004
in), which is the specified valve clearance.
Install the removed parts in the reverse order of removal.

This information came straight out of the manual.

[sargentargent]

Thought I should mention that I purchased a new oil pump chain in the box and in a sealed plastic bag. This chain is about as loose as yours. The original chain was much tighter. Think they made them longer to make it easier to get the sprocket on the oil pump. Anyway it works fine. Your engine is probably newer than mine. My buggy is over 7 years old. Just finished my rebuild. So far everything is going well. Hope it stays that way.