Did my timing chain come off?

p5200 · February 23

2000 honda trx300ex. It's been sounding like it's been cranking too fast and not hitting at all. I took the 2 valve adjustment caps off and while cranking, the valves don't move at all. Getting good spark and fuel. Surely, there should be movement with the valves opening and closing. Am I correct on this assumption? Thanks folks!

p5200 · February 23

Or maybe broken?

**Mech** · February 23

Yup.. Sure sounds like it.

Once you take the valve/cam cover off you will see if the chain's off or broken.

p5200 · February 23

Yeah, I got all the bolts out just stubborn gasket holding it on now. It is cloudy and dark here and I could see good fire from the plug shooting down in there. Is that a pretty big job to replace the chain?

**Gwbarm** · February 24

Not too bad, you have to pull the head to be able to fish the broken chain out of the crankcase

p5200 · February 24

Do you have to pull the clutch and oil pump?

**Gwbarm** · February 24

I just assumed from your last post about replacing the chain it was off, I would say if the valves aren't moving when you roll over the engine it is either off or broken, did you pull the inspection cover to see if it was there.

**Mech** · February 24

To just change the chain alone I think you'll be able to take the cam cover off, cam out, and the side cover and stator flywheel etc off, then by rotating the chain when looking from above, that is, swing the front throw of chain out away from the bike, so it'll swing around the end of the crank, and then haul it upwards. If you need to change the timing chain and slipper I think it may be necessary to take the head off.

p5200 · February 24

I pulled the two small covers to expose the valves and I could see they weren't moving while cranking the engine. I removed all the bolts from the head. It seems like the gasket has a good grip on it. Then, it started to rain so I had to quit and put a tarp over it.

Not quite sure where the cam cover is?

**Mech** · February 24

The cam cover is that top piece of/on the head assembly, it has the valve covers bolted to it. They might call it a head cover or something..

There are a couple of dowels locating the cam cover, they will be tight probably and hindering the cover lifting off. You might have to find somewhere to lever the cover up a little..

**Gwbarm** · February 24

If you are having trouble getting the head off maybe the chain just jumped off the cam gear.

p5200 · February 24

Ok Thanks, I'll get out there in the morning and see if I can get it off and see what I've got.

2 minutes ago, Gwbarm said:

If you are having trouble getting the head off maybe the chain just jumped off the cam gear.

Yeah, that's probably my luck lol!

**Mech** · February 24

You need to check the valves aren't leaking after you get the cam out.. They can get bent when a chain comes off.. on some vehicles.

Neither the cam nor the chain will be holding the cam/head cover on.. It will just be the dowels and the sealant.. if you are sure you got all the bolts out..

p5200 · February 24

I thought about using a block of 2x4 and a hammer tapping around the head. I'm not quite sure how to test for leaking valves compression check maybe? or will that just test 2 of them?

**Gwbarm** · February 24

Did you take the top cover off where you can see the cam gear chain and valves or is that what's stuck.

p5200 · February 24

I got it off and, the chain came off on the bottom gear. Is it possible to put the chain back on and maybe, use the adjuster and tighten it? I thought maybe if I lined up the bottom gear to TDC, I could then line up the cam gear marks where they go with the chain still on the bottom gear or, is that possible?

**Mech** · February 24

Tapping around the edges of the cam cover might help get it free, but I'd just find somewhere to lever it up. Sometimes there's a small overhang somewhere on the outside where you can get a screwdriver tip under to lever them up, or else poke a screwdriver into where the valves are and lever in there. Be careful not to damage any sealing faces, or clean them up with a mill file if they do get damaged.

You'll probably be able to hear the valves leaking as you turn the motor over, or feel a lack of compression and vacuum.. A compression test won't work because the inlet valves won't open to let air in, but if you turn it by hand there will be resistance of some sort, either as vacuum develops or compression develops. You could also check the valve clearances before pulling the cam cover off. . Bent valves hold the valve open and they have too much valve clearance.

If you can't decide whether the valves are bent or not, you could either put the chain and cover back on and then do a compression test, or, just pull the head off and invert it and fill the combustion chamber with fuel.. it shouldn't leak out of the inlet or exhaust..

**Mech** · February 24

For the chain to jump off it has to be really worn, or the guides and tensioners to be really worn, or the tensioner mechanism to be defective.. It's meant to be self adjusting on that I think.

To get the chain on you have to undo and remove the tensioning device on the back of the cylinder, take the cam sprocket off the cam, drop it down a little to slip the chain on, then lift it back up and onto the cam..

Edited February 24 by Mech

p5200 · February 24

Is it possible, to put a new chain on using the procedure you spoke of? According to the service manual it says it takes a special tool to adjust the tensioner.

**Mech** · February 24

I thin it's possible to get a new chain on, I've always been able to get them off with the heads on. You let the chain dangle down by the crank, then bend/fold a bit at the bottom forwards, swing that short leg out and around the end of the crank and on over it.

The special tool... I've never used one on anything.. I don't know that I've seen that particular type of tensioner but most can be reset somehow using pliers or screwdriver or a bit of wire.. Have a play with it.. It gets retracted to fit it, then once it's released there should be a spring that pushes the plunger out, and a ratchet to prevent it going back in. Check the ratchet mechanism very carefully for wear. It might have slipped and caused the problem, and the wear might only be in one place, the place it was sitting with the old chain and slippers in there. A new chain might have it sitting in a better place, but you don't want it to slip again later after the chains stretched a little .

p5200 · February 24

If I take the head off, would I also have to take the right side crank case cover off?

**Mech** · February 24

No.

p5200 · February 24

Good deal Thanks!

**Mech** · February 24

You should figure out why the chain jumped though. The chains normally last for a set of rings at least, and often longer.

If the chain or tensioner or slippers are worn they need replacing, and to do the slippers you have to pull the head. If you pull the head it's possible the cylinder base gasket might start weeping a bit of oil.. nothing much but messy and annoying.. If you are having to change the chain because of wear, and take the head off, then you might as well take the cylinder off and slip a set of rings or rings and piston in there at the same time, give the valves a quick lap in and it will probably be good for years.

**Gwbarm** · February 24

Just reading all the posts since you found the chain, no a whole lot to add except also curious why it came off , is the tensioner in tact. From what I remember you can get the chain back on like mech said by taking the gear off getting it back on the gear and manipulating it into place, hoping you have enough fingers to hold it in place hold the bolt, start the bolt at the same time, I would probably do that first just to see what's going on . I think to put a new chain on that engine you have to pull the clutch and the oil pump to get it on the crank.