Blew out a cam plug !!! Help!

[GLoweVA]

This is my first post, so, i'll try to be as descriptive as I can.
My ride is a daily drive to work every day, 30 miles oneway almost all interstate. It all started when i would lose a couple of cylinders in the rain. I thought it was just water issues with the fuel and/or the electrical. It wasn't until it started doing it on dry days that I found the problem. After searching this site, I decided to check the pick up wires. Sure enough, I had an open. Here's where I think I screwed up. I might have rotated the crank the wrong direction while messing with the vac advance. I noticed that it was a little sticky and was trying to figure out how it comes off, and rotated the crank.
So, I fixed the wires, went to go restart the bike to see if it runs better and it wouldn't catch. I thought it was flooded, so I went wide open on the throttle and full choke, then crank, crank, crank, bam! one backfire! WHOA!
Okay I let it sit for a while, again thinking it was flooded. Tried it again, this time boom, the forward(Exhaust) cam plug blew out and hit the side of the house. Freaked me out. The bike ran (barely) and there was some gasses escaping from the plug hole. Back to the forum and a whole lot of reading on the cam timing issues.
So, this is where I'm at now. My thought is that I might have slipped a tooth on the cam. I plan on taking the valve cover off, checking the timing marks, checking the valve clearances, setting the tensioner, doing a compression test, lubing the vac advance, then trying a carb sync.
Anything like this happen to any of you guys?
Did I miss anything else I can check?

Thanks, this forum is great for all of us XS owners to share our experiences and expertise.

[James England]

Why do you think you slipped a tooth on the cam?

From what you've said, your bike was running intermittently rough in the wet and then started doing it in the dry intermittently but not going BANG. You found the cause.. one of the pickup wires had a break or partial break, and you removed the pickup plate to fix the wire, right? Then you put the plate back on, started the bike and kaboom!, weird things start happening. It's not coincidence.

I think your timing is way out and that you've had a load of fuel/air mixture in a cylinder which has been given a spark at the wrong time, whilst one of the valves is open. Although not compressed, the fuel/air has gone bang on this cylinder (the one with the valve open) and blasted out the camshaft plug.

IMO you've put the pickup plate back on incorrectly or, if you renewed both pickup wires, you've got them soldered on the wrong way round. The block connector that the pickup wires go into can't be plugged together the wrong way round but the individual wires can be mixed up if you've had them both off for renewal. That or you've connected them correctly but put the timing plate back on wrong (ie rotated too far clockwise or anti-clockwise).

I had a similar situation with a 'donor' XS1100 I bought earlier this year. It was too far gone to restore but I couldn't resist trying to start it. When it did fire up, it blew back through the carb, split the airbox and then the airbox caught fire! A very hairy moment. I found out the timing was totally out and I bet that's why the bike was just abandoned for 10 years.

[CatatonicBug]

Hard to tell, but rotating the engine backwards by hand should not be an issue, as long as the Cam Chain Tensioner (CCT) was still in place. Doing that is actually part of adjusting the valves, so it's not going to hurt anything.

You can check for TDC via the plug holes, but since you will need to remove the valve cover to replace the cam plug anyway, make sure you do a valve adjustment while you're in there too.

Remember that, when starting, you don't want to turn the throttle more than just a touch. If everything is right, you shouldn't need to touch the throttle when starting.

[DGXSER]

As stated, if your cam chain tensioner is in place and holding well, you should not have caused any issues by turning the motor backwards.

I agree with James, your timing is off somewhere. If you think your cam chain is off, then certainly pull the valve cover and verify that when the timing mark is on T your dots are lined up, just because you cna never be to sure on that one. If that is all good, then recheck the wiring work you did and the assmebly of that plate. It is possible to get the plate on 180 degrees out IIRC. That could easily give you alot of grief!

[BA80]

If you took off the timing plate it's possible that you didn't get the rotor for the pick up coils back in there where it belongs.

There is a pin that aligns it the crankshaft and the rotor/centifugal advance that likes to fall out and intercourse everything up.

[GLoweVA]

I left out that I never took the vac advance off, just tried to, The bolt was really tight and I didn't feel like messing with it since I fixed the broken wire. It was just one wire, so I didn't disconnect anything, just cut and spliced the break.
Maybe it was just flooded and when it did spark, it might have been just before the exhaust valve closed and that's when boom, the plug blew out.
I thought about the cam chain, because I haven't adjusted the cam tensioner in a couple of years.
I'll look at the timing/cam dots when I get the valve cover off.

Thanks

[SFerinTEXAS]

In a wasted spark system, the spark plugs fire in pairs even though one is on its compression stroke and one is on its exhaust stroke.

Anytime raw fuel is present (like an extended cranking attempt) there is a great likelihood of a backfire on the exhaust stroke.. How enough pressure entered the crankcase to blow that cam plug out is where I'm puzzling. Valve stem seems the only path available.Might also look at the possibility of fuel in the oil. Make sure the crankcase vent is clear as well.

[GLoweVA]

I didn't think about the wasted spark thing. That could definitely explain a few things. An oil change is planned soon after all the rest of the mainenance checks listed on my initial post are done.

[planedick]

Backwards

I disagree, turning the crank backwards at all is usually disastrous. The cam chain is loose on the front and only taken up by a springy guide. You better check the timing marks and pray you didn't bend a valve...

[cywelchjr]

Yet the valve shimming process in the FSM has you moving it back and forth both directions, albeit just a small amount. I would think that at least the FSM would have a warning about rotating the engine backwards if it were that dangerous. I mean, I understand, I'm not sure how much I trust the stock cam chain adjuster, but if it don't slip I think think that springy think is going to allow the chain to skip a tooth, otherwise they would do it on rapid deceleration all the time.

[planedick]

Rapid deceleration?

The engine does not run backwards on rapid deceleration!!!!! I don't recall anything about turning it backwards in the shimming process..

[CatatonicBug]

The engine does not run backwards on rapid deceleration!!!!! I don't recall anything about turning it backwards in the shimming process..

No, the engine doesn't RUN backwards, but the force applied by the rear wheel, up the shaft, through the tranny, using ENGINE BRAKING to slow the bike, puts backward force on the engine. The CCT is NOT a "springy guide" unless you don't tighten it down. It should have plenty of tension on the chain to prevent it from jumping a tooth, especially when turning the engine by hand. Part of the shimming process requires you to turn the engine backward to avoid the tool used to hold the buckets off the lobes. You have to turn the engine backward multiple times in the process.

[3Phase]

The engine does not run backwards on rapid deceleration!!!!! I don't recall anything about turning it backwards in the shimming process..

I use the Yamaha tool to check/change the valve shims and, depending on which camshaft and valve you're working on, you have to turn the engine backwards to engage or remove the tool.

I just set up SoccerMike's XJ and his engine is fi... you know, I haven't actually heard from him since he started to put the valve cover and fairing back on this morning, I should check in and see what happened!

[GLoweVA]

Update on Cam Plug blowout

I just got done taking the bike apart. Got the seat, tank, fairing, airbox and carbs out. Saw some gunk in the carbs, so I'm setting those aside for a good cleaning. Pulled the valve cover off and checked the cam alignment. Put the timing mork on "T" and the dots lined up! WHEW! I went thru the cam chain adjustment procedure, but didn't notice any different tension in the chain. Got my feeler gages out and started measuring the valve clearances, Oh boy! Here's what I got. (1,2,3,4) Intake: .11, .10, .14, .14 Exhaust: .18, .19, .16, .14
I know these are all low out of spec. (Intake .16-.20, exhuast .21-.25)
I don't have the shim removal tool, so I haven't pulled the shims out to see what sizes I need.
My question is: Do I really need to change these out right now? Can I get away with doing it say in a month or two? I doubt these have ever been done. I've had the bike for over 7 years and the PO (ex-father-in-law) had if for about 5 years before that.
Another question: I saw some discussion on gaskets for the valve cover. Any ideas? I was thinking of just using some gasket sealer/rtv.
Thanks again for all of you guys that weigh in with your 2 cents. Every bit of information helps me make better descisions.
-george

[CatatonicBug]

My question is: Do I really need to change these out right now? Can I get away with doing it say in a month or two?

You'd be fine with waiting that long. What's another month? It just means taking all that stuff apart again.

I saw some discussion on gaskets for the valve cover. Any ideas? I was thinking of just using some gasket sealer/rtv.

The RTV in a can called "The Right Stuff" gets my vote. The only gaskets you really need are the head gasket, float bowl gasket, and the exhaust gaskets. All the rest can be replaced with RTV.