Weird compression/valve problem has happened after cam sprocket bolt came loose??????

[mattb348]

I've spent a LOT of time getting a ytm225dx to finally run right.

I've spent a lot of time outside working on it in 10 degree weather (for hours).

I'm just about at wits end here...

I FINALLY got it to run perfect (ended up having to put a different carb on it, among many other things that I already did).

But as usual now there is another issue.

Here is the deal:

I had the bike running absolutely PERFECT today. It had good compression, started right up, and ran PERFECT in all aspects.

Then later today, I fired it up again, and drove it down the driveway a ways, then it died and would not start. I noticed it didn't have jack for compression now.

I took off the cam chain cover on the side of the head, and instantly found the problem.

I never tightened the big bolt that holds the cam sprocket in place nearly tight enough (oops). It had came loose (but hadn't came out very far yet). However, it loosened up enough so that the sprocket came off of the key, and was turning freely, without even turning the cam (which is why it had crap for compression I'm assuming.... because the valves weren't working right)???

It didn't hurt anything (that I could see) when this happened, other than it messed up the cam gear a little. Luckily I had a spare, which was in perfect shape. So I threw that on, and tightened the CRAP out of the bolt that holds it in place.

I then set the timing again, which came out perfect (I'm very good at doing this because I have done it a hundred times).

Then when everything was put back together, the bike wouldn't start. And guess what? I noticed it still had CRAP for compression; it pulled over WAY WAY too easy.

The decompressor was not on.

I took the cam chain cover off again, and everything was still looking and working perfect, and timing was still just fine.

What on earth is going on NOW? This is getting to be insane!

How could it NOT have compression (or run) now just because the stupid cam sprocket bolt came loose, and the sprocket spun freely for a couple seconds as the bike died???

I'm getting real close to driving this bike off a cliff. I have an EMBARASSING amount of time into this thing, and every time I think I'm finnaly done with it, something else goes wrong (literally).

The last time I checked valve clearance it was fine. But I didn't check it AFTER this incident. However, I don't see how that could have thrown the clearance off.

And I'm pretty sure I didn't blow a head gasket or sieze rings, just because that stupid cam sprocket bolt came loose. I think it is a valve issue. But I can't understand WHY this is the case.

It ran PERFECT before this crap happened.

Anyone have any ideas?

[cr480r]

bent valve

[mattb348]

bent valve

How does the cam chain sprocket coming loose bend a valve?

[cr480r]

the piston bends the valve

[mattb348]

the piston bends the valve

That is what I was afraid of.

So the fact that it jumped timing and everything got out of sync, made the piston come up while the valves were open, and thus hit the valves, bending them?

Does this ruin the compression because they no longer seal properly?

[cr480r]

That is what I was afraid of.

So the fact that it jumped timing and everything got out of sync, made the piston come up while the valves were open, and thus hit the valves, bending them?

Does this ruin the compression because they no longer seal properly?

yep. the bent valve wont seat, thus wont hold cylinder pressure.

[mattb348]

Thanks a ton guys.

I just bought brand new valves on ebay for $30 with shipping. Not too bad I guess.

[Dirtcrasher]

Just bend the seat to the new angle of the valve

Yep, you don't decide what position the cam is in when it lets loose. Being keyed, WTH were you thinking!!!!!!! especially being so cold outside. It could have come loose and still been fine but once it was "free-wheelin", that was it. That was a bolt for "Blue Loctite" anyhow, you would have remembered then.......

I'd pull the head and inspect for damage to any and all valves/seats and guides.

Hope nothing else got damaged. So close yet so far, thats a bummer................

GL!

[mattb348]

Yup, both valves were bent. However, nothing else was hurt, valve seats are fine, etc.

I'll have it running again soon. new valves should arrive by monday probably. No biggy.

Gonna be darn sure to tighten that bolt real good this time, and I'm putting blue lock tight on the bolt too