dead cylinder

In your earlier post you talked about swapping boots and wires. But not the plugs. Are you sure you swapped the plugs. Have you seen the plug sparking? Got another to try just to be sure?

Independently my 1st test would have been to pull the plug out and plug back into HT cap and then spin engine over and look for sparks,,

If sparks are good, then remove injector and watch spray pattern compared to other injector...

Then if alls well, remove rocker cover and check valve clearances and test compressions........... Your looking for tight or non clearance at tappets.......

Here's something, I just pulled plugs and put on a compression gauge.  The right side gives a 0 PSI reading.  The left side is at 170 PSI.  Tried a couple times.  0 PSI on right cylinder.  Both sides put out good puffs of air when cranking without spark plugs.  

So I pulled head cover and looked at rockers.  They seem to be doing their thing.

Well it's obviously got a huge problem. Time to whip the head off and take a look.

jg213 wrote:

Here's something, I just pulled plugs and put on a compression gauge.  The right side gives a 0 PSI reading.  The left side is at 170 PSI.  Tried a couple times.  0 PSI on right cylinder.  Both sides put out good puffs of air when cranking without spark plugs.  

So I pulled head cover and looked at rockers.  They seem to be doing their thing.

OK... Take off the inlet rubber and the exhaust header, replace spark plug and get someone to turn the engine over with a socket wrench while you listen, down both holes, (small hose inside your ear and other end into head port) to identify if its inlet or exhaust valve thats letting by (hope piston and rings are ok)..

Have you check valve clearances???

Sounds like it's dropped a valve for some reason. No point in fannying about. Just pull the head, it's half an hours work.

Tends to make a bit of a mess if it drops a valve.

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Christ (with respect) if he didnt hear that coming, theres no helping him!

Nah. You'd be surprised.

Usual reason for these motors to drop a valve is a buggered guide. Why do the guides suddenly wear? Who knows? Could be any number of reasons. It's not common but signs things are going west aren't really 'In your face'. One member here had a valve drop, might even have been the one in the pic, I'm not sure. Anyway he rode it until it stopped and said he hadn't really noticed anything! It has to be said though that the gent in question has the mechanical sympathy of a house brick.

Charlie's Audace which we have in at the moment had a rooted guide. No evidence as to why but it was the valve adjacent to the SAS port. Relevant? Who knows?

And before the garment rending starts in thirteen years I've seen two or at most three dropped valves. It's not a common failure.

You could drop a bore scope down the plug hole, and have a look.

When it was running did it show a marked reluctance to rev above 5,500-6,000 rpm?

Pete Roper wrote:

Tends to make a bit of a mess if it drops a valve.

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Oh my the horror. Is that a hole in the cylinder?!

The cylinder is the bit the piston goes up and down in. The bit with the valve head stuck in it is the piston. As it goes up and down at even low crank speed the lost valve head does a lot of damage to the head and the piston and bore.

Even at idle speed he piston is flashing up and down twenty times a second. It doesn't take long for stuff to go pear shaped........

Yeah sorry I was talking to a friend while typing that. I meant piston.

I imagine that dropping a valve like that would be sooo loud. Surely OP would have heard it.
Could a bad clearance leading to a never fully closed valve be an explanation to the absence of compression?
What is the clearance between valves and pistons in the 8V? Would an open valve with normal gap at TDC lead to a collision between the piston and the valve?

Damn - this issue took a nasty turn!
I was hoping this would be an easy fix for you, but it's not looking good.
you're certainly at the right place for troubleshooting.
keep us posted

Rather than be a "Debbie Downer", I'm going to suggest it MIGHT be something as simple as a bit of carbon holding a valve open.

Thanks all for input.  Much appreciated.  This is definitely a little over my experience level, but I'm thinking I'll ride it out a bit.  I did download a 1200 8V service manual and it looks like pulling the head is no big deal.  Also found a tip on Google about putting some oil in cylinder and checking for bad ring.  Well I did that and still get 0 PSI.  So looking like will pull off head tomorrow and doing a visual on valves and piston top.

Before you pull the head off set the piston at TDC compression. Turn the crank clockwise as viewed from the front with a 24mm socket on the nut on the front of the crank. Use a thin screwdriver or the like to determine TDC as accurately as you can. Then when you remove the bolt that holds the cam sprocket and flinger plate onto the cam take the flinger plate off and check the cam timing. If you were to draw a line between the two bolt holes that hold the breather plate to the head that imaginary line should bisect the cam index pin which locates the sprocket to the cam. If the pin is to one side or another of that imaginary line it means the cam timing was out and that explains your dropped valve, (If indeed that is what the issue is.)

Even before this you can simply remove the exhaust manifold and do a visual check on the exhaust valves. It is usually an exhaust valve that fails as these run much hotter than the inlets. If it's shed the head it will be obvious and the port and likely the header pipe will be full of shrapnel.

If this does turn out to be the problem it would probably be cheaper to source a decent, (Rollerised!) motor second hand and slip that in rather than trying to repair the current motor. You'll need a barrel, piston kit and a head and early type heads are NLA. I might have what you need in my stash of second hand bits but I'm really not sure, I'd have to look.

I recommend doing as Pete advises. He knows this stuff.

Me - I wouldn't be able to resist a first step of dropping the headers and having a look at the exhaust valve.

Pull spark plug and dipstick. Blow air into sparkplug hole and listen at dipstick hole. If you hear air escaping, you have a holed piston.

Over reacting to symptoms can cause a lot of grief. Been there......

Been looking into checking valve clearance.  Will pull off header, find TDC, take a look at exhaust valves, check clearances.  You know, bike was running fine until it wasn't.  I was running up and down my lane just burning off fuel, then was going to put in some 0 ethanol for winterizing.  It started running rough, so I parked it thinking I was about to run out of fuel.  Put in some fuel and rode into town next day to get inspection done and some 0 ethanol, and it ran like crap, that's when I noticed the cool exhaust header.  I would say engine had been running pretty quiet as far as tapping noises or anything (up until it wasn't).

Will go out shortly and start in.  Nasty out this morning, 35 degrees F and raining.



Well, looked at exhaust area, the lower valve has a tan residue up top around valve guide area. tried checking clearance but my gauge is too thick

Then looking at intake valves one of them has come loose (dropped?). The spring is loose and valve is sitting down a ways

Guess it's time to pull off the cylinder head

Strange for a compression failure to happen quietly.

Something normally tells you -
like when i chased an LC250, two up on a BSAB50ss - the exhaust valve head came off in 3rd lol -
and i didn't catch him

Pete Roper wrote:

Before you pull the head off set the piston at TDC compression. Turn the crank clockwise as viewed from the front with a 24mm socket on the nut on the front of the crank. Use a thin screwdriver or the like to determine TDC as accurately as you can. Then when you remove the bolt that holds the cam sprocket and flinger plate onto the cam take the flinger plate off and check the cam timing. If you were to draw a line between the two bolt holes that hold the breather plate to the head that imaginary line should bisect the cam index pin which locates the sprocket to the cam. If the pin is to one side or another of that imaginary line it means the cam timing was out and that explains your dropped valve, (If indeed that is what the issue is.)

Even before this you can simply remove the exhaust manifold and do a visual check on the exhaust valves. It is usually an exhaust valve that fails as these run much hotter than the inlets. If it's shed the head it will be obvious and the port and likely the header pipe will be full of shrapnel.

If this does turn out to be the problem it would probably be cheaper to source a decent, (Rollerised!) motor second hand and slip that in rather than trying to repair the current motor. You'll need a barrel, piston kit and a head and early type heads are NLA. I might have what you need in my stash of second hand bits but I'm really not sure, I'd have to look.

Presently getting ready to pull cylinder head.  Have found a dropped intake valve.  Hoping maybe piston is ok?

Will first try and check cam timing.  This index pin, is that like a woodruff key on center shaft?

Solid pin between cam sprocket & cam. Right inside the cap/vent for cam chain sprocket. You'll see it, unless it came out a hole lined up from roller conversion(some wenches did that) that would explain a drop valve.

Stop faffing and pull the head.... Clearances should have been checked a week ago..........and you would have found the problem....