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I took on a project for a friend of a friend. This quad was supposedly rebuilt shortly before the owner bought it, likely story. Owner rode for probably 5 hours. It got to where the electric start wouldn’t start it so they would push start it and it ran fine. Then it died and wouldn’t restart. They pulled the valve cover off and found the cam sprocket bolts were loose. Put new ones in it and figured the time was of so called me.
I fixed the decompressor, the weight arm, spring, and washer was laying down inside the head. Reset timing and adjusted valves, they were all way out of spec. .017/.018” exhaust and .011/ .012” intake. Exhaust are now .010/.011” and intakes .006/.007”. Torqued everything per manual and put it back together. It will crank and crank then occasionally backfire out the exhaust.
My first thought is somehow I have the timing off so I checked it. I’ve never worked on a unicam so I thought it was weird to time off the punch mark on the drive gear and not the flywheel. When the crank punch mark is aligned with the arrow, the cam lobes are pointing towards the rear, the T mark on the flywheel is no where in sight. A lot of the videos I have watched checked the flywheel timing and it seemed to almost always line up when the crank gear was aligned. I pulled the flywheel to see if the key was sheared and it is not.
So now I am stumped. Any help would be appreciated
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Assuming you've got good fuel and a good spark plug, you might be 180* off. Cam lobes angled up and to the rear. These motors fire twice per revolution, but only the TDC spark gets fuel, the other spark is wasted, I think I'm explaining that right. So you might be 180* off. Did you remove the cam gear from the chain? Is the chain stretched? Timing needs to be set at TDC, but your marks look right, so check your at TDC with this alignment, if not rotate motor till at TDC then set your timing marks. This is why I ask if the cam gear and chain have been separated.
 

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If you set the valve lash with the timing off, you'll need to re-adjust valve lash at TDC and timed correctly. If you were 180* off the valve lash should be close but check it to be sure.
 

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It shouldn't keep it from starting, but your cam gear teeth looked rounded out, don't want to fix her up then jump time pinned in 2nd....Might compare teeth with a new gear. Rounded teeth and stretched chain would make it next to impossible to time correctly, and dangerous and expensive. My 2 cents
 

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I took on a project for a friend of a friend. This quad was supposedly rebuilt shortly before the owner bought it, likely story. Owner rode for probably 5 hours. It got to where the electric start wouldn’t start it so they would push start it and it ran fine. Then it died and wouldn’t restart. They pulled the valve cover off and found the cam sprocket bolts were loose. Put new ones in it and figured the time was of so called me.
I fixed the decompressor, the weight arm, spring, and washer was laying down inside the head. Reset timing and adjusted valves, they were all way out of spec. .017/.018” exhaust and .011/ .012” intake. Exhaust are now .010/.011” and intakes .006/.007”. Torqued everything per manual and put it back together. It will crank and crank then occasionally backfire out the exhaust.
My first thought is somehow I have the timing off so I checked it. I’ve never worked on a unicam so I thought it was weird to time off the punch mark on the drive gear and not the flywheel. When the crank punch mark is aligned with the arrow, the cam lobes are pointing towards the rear, the T mark on the flywheel is no where in sight. A lot of the videos I have watched checked the flywheel timing and it seemed to almost always line up when the crank gear was aligned. I pulled the flywheel to see if the key was sheared and it is not.
So now I am stumped. Any help would be appreciated View attachment 151765 View attachment 151766
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If you set the valve lash with the timing off, you'll need to re-adjust valve lash at TDC and timed correctly. If you were 180* off the valve lash should be close but check it to be sure.
Thanks for the response. Yes, it was brought to me separated. Cam lobes are currently facing back and slightly up when the crank gear mark is aligned. So in my mind it shouldn’t matter whether the piston was at TDC compression or exhaust when I timed it. If the cam is oriented correctly and the gear is in line with the arrow mark, it should run. Only thing I don’t get is how far off the T mark on the flywheel is.
 

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Thanks for the response. Yes, it was brought to me separated. Cam lobes are currently facing back and slightly up when the crank gear mark is aligned. So in my mind it shouldn’t matter whether the piston was at TDC compression or exhaust when I timed it. If the cam is oriented correctly and the gear is in line with the arrow mark, it should run. Only thing I don’t get is how far off the T mark on the flywheel is.
I think it will matter if you want the T mark to line up with everything. I say this because, I've never seen white paint on the bottom cam gear screw. All the motors I've seen that paint on, when aligned correctly, the paint is always on the top screw. That T mark on the flywheel is going to go around twice per stroke.
 

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Thanks Jeremy for taking the time to respond to his question!

However, I do want to clear up a few things that may just sound a little bit wrong or are a little bit incorrect.

These are wasted spark engines, so it doesn’t matter if you are 180° off, if you’re at top dead center, you’re at top dead center. The timing doesn’t have anything to do with fuel. Fuel will only be sucked into the motor by the piston creating suction, no correlation with timing.

Also, it doesn’t matter if your timing is off when adjusting valve lash. Of course I can only say that if the cam lobe‘s are pointing up as the OP said that they were. Many guys will adjust valve lash with the head on the bench and no timing chain even on it.

And, the T Mark will technically only go around 1/2 a rotation per stroke. In a four stroke engine the crank will spin two full revolutions to accomplish all four strokes.
 

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So my main question. Why aren’t the crank mark and T mark lining up together like everybody says they should?
 

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I had an 07 apart earlier this year, and when I tried to line up the clutch side timing lines, they did not correspond to the flywheel being at TDC. Those hash marks are for the balance shaft to be in time.

My recommendation is to time it off the flywheel, the line in front of T indicates TDC. You could also verify this by taking out the spark plug, and carefully placing a screwdriver on top of the piston, and slowly rotate the engine. This will give you a visual verification that you are at TDC. Then the cam hash marks should be horizontal with the lobes facing up and towards the intake.

Also, as stated before, re verify your valve clearances. What is your decompression set at? Was it set with a compression tester? And lastly, what year is it? You said 05, but then also said it had electric start, so I was a little confused.

Sent from my SAMSUNG-SM-G935A using Tapatalk
 

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Sorry, it is a 2006. I did the screw driver TDC method and the flywheel T mark was almost exactly aligned, but the crank gear was off. But again, the service manual said go off the crank gear......Lash was .006” on intake, .010/.011” on exhaust. Decompressor was .022”. I haven’t checked compression like that. I think I read 65psi with the decompressor?

Since lash was set with it timed to the crank gear, it probably isn’t right now.
 

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Is this Grant S? If so, I sent you some further info through e-mail. (I've been corresponding with a guy through e-mail with a similar issue).

For valve lash - as long as you set the lash with the cam so the base circles were on the intake buckets/exhaust roller - it should be good. You just have to make sure the lobes aren't attempting to open the valves and the valves are fully seated.

For timing and 180* out - hoser is 100% correct. Wasted spark engines can't technically be 180* out. Even if you're able to install the cam/carrier at TDC on the overlap stroke (which is very difficult to do), the engine will still run and be timed appropriately. More info on that here if you want the full scoop: Hott Boys Racing - TRX450R Cam Timing

Other things I would check:
- Flywheel key present, not sheared, and in decent shape?
- Are you timing w/ the flywheel off of the "T" and not the "F" ?
- Are you ensuring you are looking at the cam sprocket mark and cam carrier arrow "level" ?
- Cam chain in good shape?
- Cam chain tensioner functions?
- Crank gear oriented and installed properly on the crank spline and timed appropriately to the counter-balancer?
- Did the cam flange spin?
- Compression test - did some bad top-end related stuff happen when those cam bolts back out ?
 

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Aright, she’s alive! New timing chain and adjusted the valves again. Set the decompressor at .020” and it wouldn’t start. I checked compression and it was zero. I adjusted the decompressor out until I got 60psi. There is at least a .100” gap now....

So it starts up and runs but it will not idle. As soon as I take my thumb of the throttle it dies. The throttle adjusted is turned all the way in so I’m not sure what’s going on. I pulled the plastic cover off the throttle and found the accelerator pump roller was bent back so it wouldn’t open. I bent it back in place and now it won’t start. I’m pulling my hair out over here.
 

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Is this Grant S? If so, I sent you some further info through e-mail. (I've been corresponding with a guy through e-mail with a similar issue).

For valve lash - as long as you set the lash with the cam so the base circles were on the intake buckets/exhaust roller - it should be good. You just have to make sure the lobes aren't attempting to open the valves and the valves are fully seated.

For timing and 180* out - hoser is 100% correct. Wasted spark engines can't technically be 180* out. Even if you're able to install the cam/carrier at TDC on the overlap stroke (which is very difficult to do), the engine will still run and be timed appropriately. More info on that here if you want the full scoop: Hott Boys Racing - TRX450R Cam Timing

Other things I would check:
- Flywheel key present, not sheared, and in decent shape?
- Are you timing w/ the flywheel off of the "T" and not the "F" ?
- Are you ensuring you are looking at the cam sprocket mark and cam carrier arrow "level" ?
- Cam chain in good shape?
- Cam chain tensioner functions?
- Crank gear oriented and installed properly on the crank spline and timed appropriately to the counter-balancer?
- Did the cam flange spin?
- Compression test - did some bad top-end related stuff happen when those cam bolts back out ?
It runs! But won’t idle. The idle adjuster is turned all the way in and still won’t idle. Fuel needle is NGP R (or P) set at the 3rd from the bottom.
 

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Discussion Starter #19
I’ve been through the carb. Everything is clear. Starting to lean towards the cam flange has spun. Visually the lobes are pointing back, not slightly upwards.
 
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