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HOWTO - Valve Adjustment UT400


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Since I've seen some questions on this I took some pictures and will provide instructions on a valve adjustment for the UT400. This should be the same for the 550's and other various Coleman/Hisun single cylinder models with the cylinder slanted aft.

I have seen several people ask of it is really necessary, and read several reports of valves being out of adjustment from the factory. My valves were .004" intake, and .010" exhaust with about 5 hrs on the machine.  I've seen different numbers thrown around for factory spec, but I decided to go with 0.005".

This is called valve lash. What is is is a gap between the rocker arm and the valve then the camshaft isnt opening the valve. Why does it matter? If it's too large the valve doesn't open all the way, if it's too small the valve dosent close. This can cause valve damage (overheating) as well as loss of engine power (burned fuel is going out exhaust rather than pushing the piston dow).

Tools required : 5MM Allen wrench, 10MM box wrench, needle nose pliers, flat feeler gauge set, rags

First you need to remove the fan cover on the passenger side. There is a cooling vent hose on the back side, remove the hose clamp and slide it off. From there there are 4x 10mm bolts holding the cover. The forward ones can be accessed from under the seat.20220715_150009.thumb.jpg.da237d013656056e3bd11ebdcea207bb.jpg

Next remove the spark plug from the drivers side. Carefully wiggle the spark plug wire off. Grip it as low as possible and give it a little twisting motion as you pull it off to help free it. Its a tight fit for a socket, but there is a sheet metal wrench in the toolkit that fits it. Unscrew the plug and set it aside. This allows you to spin the motor over freely with no compression to fight. When you reassemble this is a good opportunity to switch to an NGK iridium plug for better performance/less fouling DR8EIX)

Next you need to remove the intake and exhaust valve covers. The intake us the forward one. There are 3x 5MM Allen screws to remove. The Exhaust is the rear with 2x 5MM Allen bolts. Both covers have O-Rings instead of gaskets and are reusable. When you remove the rear be careful and use your rags as there will be oil that drips out.

Next up we need to spin the motor over to top dead center. Grab each rocker arm and give em a little wiggle up and down. Spin the engine over by grabbing the fan with your other hand. Spin the engine over until both rockers have some wiggle and are loose.

20220715_144812.thumb.jpg.638463ab7bc08d1af3be1294d33ad14b.jpg

Once both rockers are loose slide the feeler gauge in like shown above. Try different feelers as needed to determine your starting spec. You should feel some drag but still be able to move the feeler without too much force.

If you need to adjust, use the 10MM wrench to slightly loosen the locknut, then with the correct feeler gauge in place, tighten the top square nut while wiggling the feeler in and out. Once you have it right you need to tighten the 10mm lock nut without moving the square head bolt. Once the lock nut is tight recheck the clearance.

That's it, button everything back up and make sure you have it all reassembled before running it again.

If you find this helpful give me a thumbs up or comment. If you have any questions or need more help let me know. If there's interest maybe I'll do some more of these

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  • 3 weeks later...
  • 1 year later...

My UTV400 has trouble starting when cold but starts with no problem at all when warmed up. Another UTV owner had the same problem that was resolved by adjusting the valves, but I was wondering if this could also possibly be a choke problem. Is there any way to check that our before I go through adjusting the valves?

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  • 3 months later...
On 11/19/2023 at 9:17 PM, Rainman said:

My UTV400 has trouble starting when cold but starts with no problem at all when warmed up. Another UTV owner had the same problem that was resolved by adjusting the valves, but I was wondering if this could also possibly be a choke problem. Is there any way to check that our before I go through adjusting the valves?

There's no choke on the newer hisun/coleman UTV's. They are fuel injected. The older ones were carberauted, not sure what year they switched maybe 2015-2017ish?. The older coleman branded manual incorrectly shows a choke lever on the dash, as well as some other antiquated info.

Cold start issues could be a bunch of things, I would start with valves and plug (they're right there together), move on to fuel, fuel filter, and injector, and if still having issues I would check the ECT sensor. I have heard of some failing. If the ECU thinks the engine is warm it will not inject the extra fuel required for a cold start. In the downloads section of this site there is a fairly comprehensive factory service manual for these available.

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23 hours ago, aefron88 said:

There's no choke on the newer hisun/coleman UTV's. They are fuel injected. The older ones were carberauted, not sure what year they switched maybe 2015-2017ish?. The older coleman branded manual incorrectly shows a choke lever on the dash, as well as some other antiquated info.

Cold start issues could be a bunch of things, I would start with valves and plug (they're right there together), move on to fuel, fuel filter, and injector, and if still having issues I would check the ECT sensor. I have heard of some failing. If the ECU thinks the engine is warm it will not inject the extra fuel required for a cold start. In the downloads section of this site there is a fairly comprehensive factory service manual for these available.

All my starting and running issues funneled down to water in the gas tank. Got that all cleaned out and so far, all is well and running real good.

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  • 4 weeks later...
On 7/18/2022 at 8:01 AM, aefron88 said:

Since I've seen some questions on this I took some pictures and will provide instructions on a valve adjustment for the UT400. This should be the same for the 550's and other various Coleman/Hisun single cylinder models with the cylinder slanted aft.

I have seen several people ask of it is really necessary, and read several reports of valves being out of adjustment from the factory. My valves were .004" intake, and .010" exhaust with about 5 hrs on the machine.  I've seen different numbers thrown around for factory spec, but I decided to go with 0.005".

This is called valve lash. What is is is a gap between the rocker arm and the valve then the camshaft isnt opening the valve. Why does it matter? If it's too large the valve doesn't open all the way, if it's too small the valve dosent close. This can cause valve damage (overheating) as well as loss of engine power (burned fuel is going out exhaust rather than pushing the piston dow).

Tools required : 5MM Allen wrench, 10MM box wrench, needle nose pliers, flat feeler gauge set, rags

First you need to remove the fan cover on the passenger side. There is a cooling vent hose on the back side, remove the hose clamp and slide it off. From there there are 4x 10mm bolts holding the cover. The forward ones can be accessed from under the seat.20220715_150009.thumb.jpg.da237d013656056e3bd11ebdcea207bb.jpg

Next remove the spark plug from the drivers side. Carefully wiggle the spark plug wire off. Grip it as low as possible and give it a little twisting motion as you pull it off to help free it. Its a tight fit for a socket, but there is a sheet metal wrench in the toolkit that fits it. Unscrew the plug and set it aside. This allows you to spin the motor over freely with no compression to fight. When you reassemble this is a good opportunity to switch to an NGK iridium plug for better performance/less fouling DR8EIX)

Next you need to remove the intake and exhaust valve covers. The intake us the forward one. There are 3x 5MM Allen screws to remove. The Exhaust is the rear with 2x 5MM Allen bolts. Both covers have O-Rings instead of gaskets and are reusable. When you remove the rear be careful and use your rags as there will be oil that drips out.

Next up we need to spin the motor over to top dead center. Grab each rocker arm and give em a little wiggle up and down. Spin the engine over by grabbing the fan with your other hand. Spin the engine over until both rockers have some wiggle and are loose.

20220715_144812.thumb.jpg.638463ab7bc08d1af3be1294d33ad14b.jpg

Once both rockers are loose slide the feeler gauge in like shown above. Try different feelers as needed to determine your starting spec. You should feel some drag but still be able to move the feeler without too much force.

If you need to adjust, use the 10MM wrench to slightly loosen the locknut, then with the correct feeler gauge in place, tighten the top square nut while wiggling the feeler in and out. Once you have it right you need to tighten the 10mm lock nut without moving the square head bolt. Once the lock nut is tight recheck the clearance.

That's it, button everything back up and make sure you have it all reassembled before running it again.

If you find this helpful give me a thumbs up or comment. If you have any questions or need more help let me know. If there's interest maybe I'll do some more of these

 

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They both need to be fully off their respective cam lobes. You can either look at the cam or pull the spark plug and look through the hole with a flashlight. It's much easier to spin the engine over by hand with the plug pulled since you're not fighting the compression.

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