Low compression

[Tony Wheeler]

Originally Posted by Malcolm Towrie

Oil rings are good. No smoke, and no carbon on plugs or valve/head visible through plug hole. The carrier was running OK last summer and fall in parades and displays. It started and ran OK just before I did the compression test two days ago

Hmmm....motor doesn't blow smoke, doesn't foul plugs, performed OK in parades last year, started and ran OK two days ago. And the problem is....what exactly....?

[Malcolm Towrie]

Tony, the owner likes his equipment to be in good condition, but as I think you are suggesting, he's resigned to running the carrier as-is over the summer.

I'll certainly pull the plugs again and give the accessible valves a "nudge". I was surprised I couldn't hear clearly where the leakage was coming from during the leak-down test, so valves stuck open enough that they don't hiss could be the explanation.

Thanks for the suggestions.

Malcolm

[rob love]

On mine, every valve that was stuck was directly under the spark plug hole.

Again, I think that for any amount of work an a carrier engine, removing the dog house will actually save time. You could build a stool with four legs that sorround the transmission and actually sit down to work as opposed to crouching, twisting like a controtionist, and sticking your head in the dark space. If nothing else, I suspect the quality of work will be better.

[Malcolm Towrie]

It looks like the valve under the plug hole is the exhaust valve so it makes sense that that valve is more likely to stick.

Have you had it apart since? If so, did you find the valve springs weak or varnish build-up on the stems?

And after taking another look, Lynn's right. Those heads are not coming off without removing that angle iron rail, so my thought of simply pulling heads and intake off to do a quick fix isn't going to fly. And from what I have heard and read, doing valve work on this engine isn't that simple anyway.

Malcolm

[RichardT10829]

The valve stems bend so easily on these engines... You will find that they run ok, but the valves won't seat tight into the block.

[Malcolm Towrie]

Update: tapping on the valves with a brass punch on the worst cylinders (with the pistons at TDC firing) had no effect. I measured the height from the head of each valve to the spark plug seat with dial calipers before and after and there was no change. And no change in compression pressure. Oh well, it was worth a try.

It's unusual to bend valves on a engine especially as the usual causes like over-revving or cam timing slipping aren't applicable on a flatty. Why are these engines prone to it?

Malcolm

[rob love]

A valve job in the original form is a big deal. You grind the valve and the seats,, then you grind the stem of the valve to get the right clearance. You can install adjustable valve lifters (I think they originally come from one of the old 8N Ford tractors but don't quote me on that). That will make it a lot easier to do the adjustment, but it requires removal of the cam I think, which is not something you are going to do in-frame.

Can't say I have ever had a problem with bent valve stems on a Ford.

[Tony Wheeler]

Originally Posted by Malcolm Towrie

Tony, the owner likes his equipment to be in good condition, but as I think you are suggesting, he's resigned to running the carrier as-is over the summer.

Yes I was suggesting there's no immediate problem Malcolm. You seem hell bent on removing the heads prematurely.

Originally Posted by Malcolm Towrie

I'll certainly pull the plugs again and give the accessible valves a "nudge".

Actually I'd hoped to save you the trouble by pointing out that the motor is ALREADY running well. That's impossible with stuck valves. Perhaps I should have elaborated as it can be difficult to visualize:

The so called "stuck valve" or "sticky valve" syndrome common to flatheads is caused by corrosion of exposed valve stem on open or partially open valves during long standing - the result being a snug fit in the guide which cannot be overcome by the puny valve spring. Hence while the valve will OPEN fully and freely, it will stop on the way down when the band of rust on the stem hits the guide. Symptoms are ZERO compression, and if it's an intake valve, some audible blowback through the carby when cranking over. Such a motor will definitely not run! The solution as Rob describes is to "tap it down, crank the engine, tap it down again, crank the engine...." Generally after several repetitions accompanied by ample lubrication of the valve stem it will require only a single light tap, whereupon the valve will snap shut under valve spring pressure with a satisfying "plop". Thereafter a few more repetitions will generally see the valve no longer sticking at all.

The point being that stuck valves, once unstuck, cannot become restuck! Once they're dislodged and start moving again the corrosion quickly rubs off and the valve will seat normally - particularly once the motor starts running. The idea that valves might stick partially open is a mechanical impossibility. For example, consider a motor running at 3000 rpm, with the valves hammering up and down 25 times per second. No collar of rust on the valve stem can persist under those conditions.

re: I added oil to #7 and no change, still 30psi. So not rings, at least for that cylinder. I'm thinking, pull the intake manifold and heads and check bores, valves, guides, seats, head gaskets.

You're certainly itching to pull those heads off Malcolm! Can I suggest you restrain yourself long enough to perform wet and dry comp test on ALL FOUR deficient pots. That way you'll be in a position to confirm your "not rings" diagnosis.


re: This carrier is in very nice, restored condition and the engine was supposed to have been rebuilt. Looks like it wasn't.

I'm probably clutching at straws here, but it's just possible the motor WAS rebuilt and the valve clearances were insufficient. It's not unheard of and it can lead to valves not sealing perfectly after running in, because the clearance is further reduced as the new valves and newly ground seats bed in. This would be consistent with compression readings: 90-95 psi indicating rebuilt motor; 30-50 psi indicating zero valve clearance on those pots. It would also explain: "Oil rings are good. No smoke, and no carbon on plugs or valve/head visible through plug hole." That does not sound like a tired old flathead with burnt valves.

In any case the heads should not be removed until this possibility can be excluded. That means removing the intake manifold and checking valve clearances. Yes it may be wishful thinking but you never know your luck sometimes!

[Malcolm Towrie]

Originally Posted by Tony Wheeler

Yes I was suggesting there's no immediate problem Malcolm. You seem hell bent on removing the heads prematurely.

Actually I'd hoped to save you the trouble by pointing out that the motor is ALREADY running well. That's impossible with stuck valves. Perhaps I should have elaborated as it can be difficult to visualize:

The so called "stuck valve" or "sticky valve" syndrome common to flatheads is caused by corrosion of exposed valve stem on open or partially open valves during long standing - the result being a snug fit in the guide which cannot be overcome by the puny valve spring. Hence while the valve will OPEN fully and freely, it will stop on the way down when the band of rust on the stem hits the guide. Symptoms are ZERO compression, and if it's an intake valve, some audible blowback through the carby when cranking over. Such a motor will definitely not run! The solution as Rob describes is to "tap it down, crank the engine, tap it down again, crank the engine...." Generally after several repetitions accompanied by ample lubrication of the valve stem it will require only a single light tap, whereupon the valve will snap shut under valve spring pressure with a satisfying "plop". Thereafter a few more repetitions will generally see the valve no longer sticking at all.

The point being that stuck valves, once unstuck, cannot become restuck! Once they're dislodged and start moving again the corrosion quickly rubs off and the valve will seat normally - particularly once the motor starts running. The idea that valves might stick partially open is a mechanical impossibility. For example, consider a motor running at 3000 rpm, with the valves hammering up and down 25 times per second. No collar of rust on the valve stem can persist under those conditions.

re: I added oil to #7 and no change, still 30psi. So not rings, at least for that cylinder. I'm thinking, pull the intake manifold and heads and check bores, valves, guides, seats, head gaskets.

You're certainly itching to pull those heads off Malcolm! Can I suggest you restrain yourself long enough to perform wet and dry comp test on ALL FOUR deficient pots. That way you'll be in a position to confirm your "not rings" diagnosis.


re: This carrier is in very nice, restored condition and the engine was supposed to have been rebuilt. Looks like it wasn't.

I'm probably clutching at straws here, but it's just possible the motor WAS rebuilt and the valve clearances were insufficient. It's not unheard of and it can lead to valves not sealing perfectly after running in, because the clearance is further reduced as the new valves and newly ground seats bed in. This would be consistent with compression readings: 90-95 psi indicating rebuilt motor; 30-50 psi indicating zero valve clearance on those pots. It would also explain: "Oil rings are good. No smoke, and no carbon on plugs or valve/head visible through plug hole." That does not sound like a tired old flathead with burnt valves.

In any case the heads should not be removed until this possibility can be excluded. That means removing the intake manifold and checking valve clearances. Yes it may be wishful thinking but you never know your luck sometimes!

Your post and its annoyed tone puzzle me, Tony. You say the motor is running well, yet it has 2 cylinders with 30 psi compression. Yes, it starts and drives, but it is not a well-running motor IMO.

I didn't think for a minute that valves stuck open because of long storage was the issue here, for the reasons you explain in such detail, but I suspected the springs on these engines were fairly light, so maybe varnish build-up on the stems or carbon on the seats preventing some valves coming down tight? A long shot, but the tapping the valves idea was suggested and it was easy to do, so why not?

So as a newbie to these engines, with the heads so temptingly accessible, it seemed a simple job to pull both the heads and intake manifold and check for ALL the various top-end related issues that could be causing this, AND fix them in the time we had available. All in one fell swoop.

Of course, now I know it isn't that simple to pull the heads, nor is it that simple to do a valve job on these engines, so we'll just run the old girl as-is until there's a space in her schedule to do the work.

Malcolm

[Tony Wheeler]

Originally Posted by Malcolm Towrie

Your post and its annoyed tone puzzle me, Tony.

I think you've misread me Malcolm. It happens sometimes in this kind of forum. It's probably my lame attempts at humour. I assure you I'm not annoyed!

Originally Posted by Malcolm Towrie

You say the motor is running well, yet it has 2 cylinders with 30 psi compression.

Yes, that's what you reported Malcolm: "The carrier was running OK last summer and fall in parades and displays. It started and ran OK just before I did the compression test two days ago, even with horrible compression on 4 of 8 cylinders."

It's not uncommon to find minimal compression in several pots on these old flatheads. They'll still run happily for many years to come, and if restricted to parades they'll probably outlive the owner. Even in hard use they remain indestructible - my F15A road truck shows 40-70 psi in all pots and rattles alarmingly when cold, but after warm up I never hesitate to wring every last screaming rpm out of it through the gears. I'm sure Jacques if he's reading this will attest to its performance up steep mountain tracks - albeit at 4000 rpm! In practice, apart from a thirst for oil, it's a perfectly serviceable motor, and I enjoy not having to nurse it like a $5000 rebuild.

Of course, being accustomed to modern motors, it can be quite disconcerting to see readings of 30 psi, and the natural response is an overwhelming urge to pull the heads off and investigate. Perhaps that's why most owners avoid performing compression tests! However, we need to remind ourselves that compression tests are purely diagnostic, and pots showing 30-50 psi at cranking speed will still produce plenty of power.

Originally Posted by Malcolm Towrie

Yes, it starts and drives, but it is not a well-running motor IMO.

This seems at odds with your earlier report Malcolm: "The carrier was running OK last summer"....."but it is not a well-running motor IMO." I guess it comes down to one's definition of "motor running well". To my mind, if a motor is firing on all cylinders, and drives the vehicle satisfactorily, it's "running well". It may be down on power, but that's a different question. That's generally tolerable on MVs, thanks to plenty of gears and no need to keep up with traffic. Indeed, lack of power is arguably essential to the MV driving experience!

Of course, I fully understand your earlier point: "the owner likes his equipment to be in good condition". Particularly when: "This carrier is in very nice, restored condition and the engine was supposed to have been rebuilt." I too would be keen to address low compression issue in such a vehicle. I was merely urging forethought and proper diagnosis.

Originally Posted by Malcolm Towrie

the tapping the valves idea was suggested and it was easy to do, so why not?

I suspect there was some misunderstanding / miscommunication here Malcolm. It wasn't immediately clear from your initial post that YOUR motor was already running, and in Ron's discussion of stuck valves it wasn't immediately clear that HIS motor was not running! Again, it's inevitable with this kind of information exchange. As you say, no big deal in this case.

Originally Posted by Malcolm Towrie

So as a newbie to these engines, with the heads so temptingly accessible, it seemed a simple job to pull both the heads and intake manifold and check for ALL the various top-end related issues that could be causing this, AND fix them in the time we had available. All in one fell swoop.

Yes, it's always tempting to whip off those heads, but in practice it achieves very little. Unlike OHV heads you can't send them away for a valve job! Unfortunately the "quick fix" you were hoping for does not exist on flatheads, because the "top end" is actually in the block.

Originally Posted by Malcolm Towrie

Of course, now I know it isn't that simple to pull the heads, nor is it that simple to do a valve job on these engines, so we'll just run the old girl as-is until there's a space in her schedule to do the work.

I think that's basically what we were advocating Malcolm, as the time frame seemed unrealistic, and the diagnosis unconfirmed. As Lynn says: "if the engine has become tired you might end up with a big job on your hands." Another possibility yet to be ruled out is broken rings, which can also occur in a poorly rebuilt motor. If I were you I'd be keen to complete the wet and dry comp test, and if it all points to valves as we suspect, I'd be keen to remove the intake manifold and check clearances.

Anyway good luck with it Malcolm and keep us posted with any developments.

Cheers,
Tony

[Lynn Eades]

I myself am wondering what else can affect the compression of the four centre pots?

[Tony Wheeler]

Yes I noticed that too Lynn, seems rather a coincidence. The mathematical probability is: 4/8 x 3/7 x 2/6 x 1/5 = 1/70. In other words, in a motor with 4 deficient pots, the odds of them all being centre pots is 1 in 70. It's quite suspicious but I can't think what it might indicate, unless perhaps BOTH head gaskets are leaking between adjacent pots, which is quite some distance in this case.

Of course, the effect of this 1 in 70 chance is that all four weak pots fire consecutively, followed by all four strong pots, followed by all four weak pots, etc. In terms of crankshaft acceleration / deceleration it's the worst possible combination.