engine miss, pushrod too low

[scottyrocks]

I seemed to have developed a miss on cylinder #1. I figured out which cylinder it was by pulling and reattaching spark plug wires, one at a time.

The inside (intake?) rocker on #1 has to be screwed in noticeably further to get .006 clearance than the exhaust rocker or both rockers on cylinder #2. Even then, it is still missing on that cylinder. This tells me that the pushrod is sitting too low in the tube, and that the intake valve is not closing, or moving at all?

I removed the rocker arm assembly, and the push rod under the intake rocker. It looks perfectly okay. Its straight and the ends are domed and smooth.

Why is the pushrod sitting too low? What am I faced with down there?
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[Pruneman99]

When you took the rocker assembly off, were all the valve tips even?

I'm not able to fully picture what you're describing but I'm thinking the intake valve is stuck open.

[scottyrocks]

[calvinater]

Rubber mallet?
_________________
"Albatross"!

[Dougy Dee]

If its stuck a few taps with hammer may persuade it.
BUT,
If the seat has come loose and jammed it open then... time for teardown. Do a leakdown to confirm, confound and confuse.

[ashman40]

With the rocker assembly removed, lay a straight edge across the valve tips. They should all rest at the same height. If one is noticeably higher/lower than the others there is something wrong. Lower could mean that valve may be stuck and not fully seating. Higher, and that valve may have stretched or the valve seat pounded into the head.

As an example, I found this pic from the gallery showing two intake valves that are slightly lower than the outer exhaust valves.

This pic was actually an example of low quality control with new out of the box heads, but you get the idea. The valves should all be resting at the same height.


You say your valve is not closing, but have you taken the above measure to show it is a problem with the valve?


One other thing to look at... pull the pushrod out of the head and roll it on a flat surface. Do you see it wobble? This would indicate the push rod is bent. A bent pushrod would also require the rocker arm adjuster be extended to compensate for the shorter overall length.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Pruneman99]

Thanks for grabbing the pictures Ashman. That was what I was trying to say in my first post.

A few things can cause excessive gap:

Valve stuck open. It may have gauled to the guide, and now it's stuck.
Valve not seating all the way due to mechanical damage. Possibly it became bent, or the seat could have fallen out and is now holding the valve open.
Excessive wear in the litter cup, pushrod, or rocker.
Collapsed hydro lifter (if applies)

[scottyrocks]

I will do the the two checks described above. I have a short level and a steel rule that are perfectly straight. I also have a glass table top that I know is perfectly flat (to roll the pushrod on).
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[scottyrocks]

I pulled off the valve cover and rocker arm assembly, and then laid a steel straight edge across the tops of the valves, as shown in the picture earlier in this thread.

I couldn't really tell if all the valves were touching the straight edge, so I put a small flashlight up there and shined it downwards over each valve stem at the straight edge. No light passed through any of them so I'd say they were all touching.

I also checked the pushrods (on the side in question). They are all straight and the ends are unblemished.

After the battery had been fully charged, I reinstalled the rocker arm assembly, adjusted the valves, changed the oil, and started 'er up.

Re the valve adjustment: I had written here earlier that the intake valve-in-question's adjustment was way off compared to the other ones. On this adjustment everything was normal, as it always had been. A good sign.

So, upon startup it ran on all four, smooth as silk. Gave 'er some gas, revved as clean as could be. I was happy, but not entirely convinced all would remain well. I hopped in, and eased off down the street.

By the time I got to the corner (about 800 ft away), it had begun to break up, and by the time I hit the next corner (another 300 ft), she was back on three cylinders.

I continued around around the block and back into my driveway.

I bought a compression tester (that I wrote about in a compression tester thread here) but, in short, have not been able to use it yet due to the limited space available to attempt to spin the hose into the spark plug hole.

But more to the point, given what happened on that very short test drive, why would an engine run perfectly cleanly for a minute or so after startup, and then lose a cylinder shortly thereafter?
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[61SNRF]

Is the engine recently rebuilt or were the heads rebuilt with new guides?

If a valve, #1 intake on your case, is too tight in the guide it can move freely when cold but seize up and stick open when hot.

This seems to fit your symptom. Somehow since your last post in 2021 the valve closed and you where able to adjust it normally.
After your brief drive it got hot and stuck open.

One thing you might do is check the valve clearance again. If it's not what you set it at before then it could be a stuck valve.

If you find it too loose again as suggested try gently tapping on the valve head to see if it frees up and closes.
That, or with the rockers off see if the valve installed heights are all the same.
Or you can do a compression test, with an intake stuck open that cylinder will be near zero.
If your hose is too long just twist, curve and/or bend until you can get it started in the plug threads.
_________________
-Bruce

An ounce of prevention is worth a pound of cure.

[scottyrocks]

SNRF,

Everything you wrote makes sense. Thank you.

I have had the car since Fall of 2016. I know virtually nothing of its service history.

Eight months have passed since I last finagled with the car so it makes sense that a stuck valve could pop back into place.

Before I attempted anything today I started the car to see what would happen, and it was running on only three cylinders. Assuming I could thread the gauge hose in I was expecting very low-to-no compression on that cylinder.

I will devote time tomorrow to getting the gauge hose to thread in properly. Whether or not I can get the gauge to work, so as to confirm what may indeed be a stuck open valve, I will check the clearance on that valve, as well. If it is huge, it's pretty obvious at this point that the valve is sticking open. To confirm, I will then remove the rocker and apply the straight edge to the tops of the valves, and note if the valve in question is not touching the straight edge. Then tap it with a mallet, re-check with the straight edge, reassemble the rocker, re-adjust the valves, and restart the engine to see if I get all 4 cylinders. If I do get all 4, even for a short time, at least I'll know what the issue is.
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[Pruneman99]

If it's getting stuck when it warms up, it will be pretty obvious. Your looking for a gap between the valve tip and the adjuster of 1/8" or more. I had a lawn tractor do this after sitting.. the valve was held completely open. Like 1".

Unfortunately if the valve guide clearances are on the tight side, old ethanol fuel will tar up enough to stick them. Usually after a bit of warm up..

[scottyrocks]

Well, it ran in the driveway for maybe a minute, and then I eased it down the block less than a thousand feet before it started missing, then another few hundred feet until it was down to three full time. Air temp was in the high 60s. Is that enough time to warm up?

When it got stuck last September I was driving it regularly, as in about 3 times a week, so the gas was never old. Do you think it's worth trying a Techron-type product or something like MMO help to free it up?

I'm getting a strong feeling that the cylinder head will have to come off to make this right.
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[Pruneman99]

[scottyrocks]

[scottyrocks]

Whelp, it seems I won't need to do a compression test.

Intake valves 1 and 2 are below level, and level with their spring collars(?) whereas the exhaust valves are slightly above them, as checked with the straight edge.

Interestingly, before I removed the rockers, I noticed that both valves on #2 had huge amounts of play, and not .006 as I set them 3 days ago. #2 was at TDC when I noticed this.

Attempted to spray some carb cleaner into the valves but the springs prevent any type of extension straw from going in to where I suppose the fluid is most needed. So I just shot it in there as best I could.

Then I placed a wooden dowel on the valve heads and hit them several times with a rawhide mallet. No change. Is this a process that takes a few tries, as with rust penetrants on stuck hardware?

If they do free up and stay freed up I will consider the matter closed, but I am not convinced that is a strong possibility.
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[Pruneman99]

So now you have multiple valves sticking? Well that pretty much confirms the hypothesis that the valve guides are too tight.

Well there is good news and bad news.

Bad news is you need to pull the engine and pull the heads.

Good news is you don't need to buy any parts. You just need to take your heads to get the valve guides reemed, then put it all back together!

[scottyrocks]

Okay, that's cool, kinda. haha

Now I just have to decide if I'm gonna do this myself with a garage full of house project stuff (for the projects I am in the middle of which means another year without driving the car), or bring the whole car to a local VW specialist and have them do it.
_________________
“If you care for a thing long enough, it takes on a life of its own, doesn't it? Mending old things, preserving them, looking after them – on some level there's no rational grounds for it.”
– D. Tartt, 'The Goldfinch'

[scottyrocks]

[MrGoodtunes]