No Compression in #2

[Rickrod3]

Could not get #2 cylinder to run had spark and gas since plug had gas on it.
Tested compression , the lowest reading on the gauge is 25 psi and it did not move. on the #2 cylinder #1 had 140, #3 had 152 #4 had 155.

I pulled the valve cover.
I put the cylinder to TDC pumped in air with a hand pump about 30 psi
the cylinder seemed to hold it and could not hear any leaks.
with the lack of compression I expected the leak to be apparent.
thought maybe a stuck valve did another compression test.
Same lack of compression.

checked valve clearances.
79F intake .006-.008 in Ex.008-.010 in
1,3,and 4 were in spec.

#2 had .005 intake and .032 exhaust.

could the .001 of an inch be causing a my compression loss?
Does the .032 large gap indicate a bent valve. If so why would just one valve bend?
Not that I'm hoping it is.

Thanks in advance
Rick

[petejw]

Hi Rick,
What you could do to check if the intake valve is leaking,
remove the carbs and intake manifold for the no2 carb.
with the crank on tdc and valves closed pour some petrol into the intake
port if its leaking it wont hold.
Did the cam timing all line up.

I had a similar problem as you but i burnt a valve.

[Larrym]

The Cold Equations...

Rickrod3,

checked valve clearances.
79F intake .006-.008 in Ex.008-.010 in
1,3,and 4 were in spec.

#2 had .005 intake and .032 exhaust.

From the Clymers Repair Manual page 44:

"Measure the valve clearance with a metric feeler gauge as it will be easier to calculate pad replacement described later in this section."

I just had to bust you for that one. I know that one can use an "American" feeler gauge set to do the measurements but then ya gotta go through all that "conversion" crap. Each time one performs a mechanical operation or a mathematical operation (conversion...) there is the possibility of human error.

Does the .032 large gap indicate a bent valve.

I'd say that yes, the larger clearance on #2 along with the lack of compression is a tell-tale for the bent or (???) valve.

If so why would just one valve bend?

How they can get bent is that they impact something ...anything while in the open position. This includes turning the camshafts (opening/closing valves) while on the bench where the valve can hit a hard surface. On the engine while the head/camshafts are installed and some of the valves are in the open position yet the pistons aren't exactly where it should be. Makes it a real challenge to work with an overhead valve train, don't it??



If the #2 valve is bent, I'd look at the precise details of the sequence, position, and arrangement of the pistons, camshafts, camchain, and valves during the reassembly process. If it got bent during the installation then you're seriously gonna have to have a sit-down/face-to-face talk with your assembly tech. Somewhere along the way he missed something. (7 outta 8 done right ain't bad though..)

Don't get mad at him or threaten to fire the guy. He prob'ly will feel bad enough already. Try to educate him so he won't make the same mistake twice. I'd rather work with a guy who bent a valve and learned how to prevent it from happening again rather than some ham-handed dude who was convinced that "it would never happen to me."

[Geezer]

I second the bent valve.

Geezer

[tw1980]

Yeah no compression is a bad thing.Pull the head and look.Hopefully it's a bent valve. If not I think I still have a couple of stock pistons. Terry

[Rickrod3]

Vowing to never let it happen again. or never say never

Don't get mad at him or threaten to fire the guy. He probably will feel bad enough already. Try to educate him so he won't make the same mistake twice. I'd rather work with a guy who bent a valve and learned how to prevent it from happening again rather than some ham-handed dude who was convinced that "it would never happen to me."
__________________

Removed a few parts to get ready to remove the head this weekend or sooner if possible.

I have been spinning the engine studying its sequence of operation.
I'm having a difficult time understanding how just one valve can be out of time. I don't claim to be an expert or doubt I make a mistake. I just think if the timing was wrong more than one valve would be damaged.
If there is a possible way please enlighten me.

I do recall a misshape while shimming them on the bench. I shimmed one side and due to inexperience left the cam shaft on and proceeded to shim the other side. I do recall a valve collision. Due to wish full thinking and inexperience I didn't think it caused any damage.
Maybe yes maybe no
For that to be the case I would have had to make a second mistake in the shimming process. Unless I shimmed the exhaust valves first and damaged it with the intake. Its possible.
I would appreciate your thoughts.

Maybe all of you already know this but I realized some thing when checking valve clearance. I lined up the dots on the cams and noted the cams position. The intake seemed to be pointing @ 11 o'clock and the exhaust @ 1 O'clock. I would think that would be the most accurate spot for checking valve clearance. The manual says the lobe opposite the shim. 11 and 1 o'clock sounds more precise (to me anyway). I have read threads where the cam lobe position was in question.
PS. I was a little sad taking her apart again

Rick

[bikerphil]

I do recall a misshape while shimming them on the bench. I shimmed one side and due to inexperience left the cam shaft on and proceeded to shim the other side. I do recall a valve collision.

Yep, it doesn't take much. On the dead cylinder, if you have an unusually large valve clearance, she's probably most definitely bent.

[Larrym]

Great Mechanical Expectations

Rickrod3,

Your gettin' it: Hands are what we use to manipulate tools but the mind is what we use to manipulate the hands.

I just think if the timing was wrong more than one valve would be damaged.
If there is a possible way please enlighten me.

The correct mechanical timing between the crank(pistons) and the valve cams(valves) serves to let them "all get along" with each other. I mean that physically the pistons and the valves get real close/cozy when at TDC and the valves open expecting the pistons to be outta the way. ( Or depending on the way you look at it, the piston does his own thing expecting the valve to have left a space just for him to occupy.)

Your right: if the timing was off between these two playmates (Crank/valve cams) it would apply to all pistons and all the valves. It's called a "shared fate" scenario and bending one valve would be followed by the next (Fat-dumb-happy) valve and piston in the firing order meeting each other unexpectedly. (Kiss.Kiss) The next revolution would repeat the process.

But that's when the starter button is pushed or something like that. When re-assembling the motor and turning things by hand all rules are off. Full revolution, partial revolution, forwards, backwards, correctly timed, incorrectly timed, crank/cams separate or in unison, anything can happen.

That's why it's vital to have the cams/crank precisely where they need to be then connecting them with the cam chain. Bumping either of them a few degrees can cause one piston/valve to meet up in whichever cylinder is in the right (WRONG!!) part of the "suck-squeeze-bang-blow" cycle where the valve is extended.

Dont'cha just wish someone would post a video of what could be seen by one of those "mini-cameras" inserted through the spark plug hole?? We'd all get to see just how close everything comes to hitting each other even when the mechanical timing is dead on.

The more an internal combustion engine is designed to achieve the best performance possible, the closer it gets to destroying itself when the slightest thing get's outta wack.

[Rickrod3]

Bend Exhaust valve confirmed

http://s910.photobucket.com/albums/a...nt2ExValve.jpg


Non of the others seem to have any damage so I guess I bent it on the bench.

Well get it right this time around.

Rick

[Larrym]

Bent or otherwise: Valve Afterlife

Drat!!

I had my fingers crossed hoping that it was just an imperfection in the sealing surfaces between the valve and valve surfaces. That another "dedicated lapping session" would fix it for ya.

Are valves like Dogs?? I mean bent or not, when they die do they go to heaven?

[clcorbin]

http://s910.photobucket.com/albums/a...nt2ExValve.jpg


Non of the others seem to have any damage so I guess I bent it on the bench.

Well get it right this time around.

Rick

Don't feel too bad Rick. I did the exact same thing to an exhaust valve while replacing a pair of valves bent from a broken timing chain. I had the bright idea to set the lash on the bench and then followed that idea up with the STUPID idea of bolting BOTH cams down at the same time...

Sure enough, I pushed an intake valve into the side of an exhaust valve. Thankfully, I had a few spares AND it only bent the exhaust valve.

[Rickrod3]

May be allittle low but: I got compression.

I received the valve yesterday and put it in.
After the installation I got the proper valve clearance of .008in.
I know I'll start using the metric side of the feeler.
Engine has not been started in a few weeks, I took the compression cold carbs and exhaust still have not been put back.
I was a little disappointed to only have 105 psi.
As I understand it will be higher with the engine warm.
Its probably high enough for the cylinder to fire.

Rick

[Rickrod3]

May be a little low but: I got compression.

I received the valve yesterday and put it in.
After the installation I got the proper valve clearance of .008in.
I know I'll start using the metric side of the feeler.
Engine has not been started in a few weeks, I took the compression cold carbs and exhaust still have not been put back.
I was a little disappointed to only have 105 psi.
As I understand it will be higher with the engine warm.
Its probably high enough for the cylinder to fire.

Rick

[randy]

Rick, did you lap the valve in?

[Rickrod3]

Rick, did you lap the valve in?

Yes I did.
I'm going to reshim the intake it was .005 Spec. is .006

Rick