So if you look at the valve stems, is one slightly higher than the others? If so that points to a sunk seat. That carries the risk of the seat coming loose from the head, which will mean you'll be pulling the engine to put it right. It can still be fuel tight and sunk.

I found a sunk inlet on No 1 cylinder on my T4 engine when I pulled it - quoted £150 to have the head cleaned and a new seat installed but I was happier getting a new head.

Personally I'd fix it asap.

 

if the seat is loose , it will raise the port wall bellow it. best thing is it may just have been re cut deeply.

 

When I was cleaning up the head and lapping the valve in I did think it looked a bit odd, but under the seat there was no gap or any evidence that the seat had pounded its way into the head. Am a bit confused now haha.

Have just run the engine and it sounds very tappety on the left side, like the sound a Type 4 head makes with a dodgy hydraulic tappet? Have triple checked the clearances and that the rocker gear is affixed tightly.

This all makes no sense to me - I took it apart as the left head was being noisy, now with new valves and a good clean out its even noisier?

 

On the up side I've taken it down the road and it runs like a beaut! any more tips on the tapping problem would be great though

 

I don't really want to take it out and strip it down again

I guess it's that ^^^^ ....... or this vvvv.

 

Type IV valve seats are notorious for falling out. Type I seats are not so bad.

First of all, are you sure you had all the same valves? Worth checking. An engine fitted with incorrect valves sometimes can still run! They just don't sit right, and don't last long.

If one is deeper in then the rest, then perhaps it was a past repair. Valve seats are simple to make and can just be made on a lathe, providing you can get the correct material stock. That's how unleaded conversions to iron engines (not VWs, as they are unleaded friendly anyway) and valve seat changes happened in the olden days apparently.

It is therefore possible that perhaps that head dropped a seat and then was fitted with a non-factory seat.

The other thing which was far more common was valve seat re-surfacing. If a valve failed and damaged the seat, they would just use special tool which looked like specially shaped abrasive grinder bit to basically re-cut the surface deeper into the existing valve seat, in situ. This is not like lapping, which removes tiny amounts of material, but is much cruder, and capable of removing whole mm of material.

If this kind of repair is carried out to only one seat, it will indeed make the valve sit deeper.

Or perhaps it was just an oddity. Maybe the seat-making machine at the factory had a malfunction and cut it too short, and nobody noticed and it went on to the pressing machine, and was pressed into your head and carried on without being noticed. Or the machine that cut the bores for the seats into the head cut too deep. Or something. Thats uncommon with VW, but not un heard of. No production line that makes millions of items is ever 100% perfect.

 

thanks Moby :lol:
Thanks for the info Adi - Both the heads on the engine are VW Mexico branded - i've been informed as this is correct for the engine as its a fairly late '78 engine - apprarently the heads for these were fabriacted in Mexico and shipped to Germany for assembly - I suppose the factory in Mexico, being a bit less quality focussed, could have put in a lower seat by accident?

All I really know albout this problem is:
- that it was there before and after I rebuilt the top end, but is now worse,
- is only on the left side when facing the engine bay
- noise seems to be 1/2 the frequency of the engine speed, so must be cam related
- Is the same when the engine is cold and hot, so cant be clearance
- is bloody annoying! " Tak, tak, tak, tak, tak"! - thing sounds like an old diesel!

 

it might be possible to get the seat out and use some of this liquid metal putty to re-seat it. I don't know if this will work but its pretty strong my only doubt is whether it would take the temperature. so if you do this its at your own risk.

 

Noooooo. Using chemical-metal on a valve seat will definitely NOT work!

Besides, valve seats are interference-fit. They are cut slightly larger then their bore and are pressed in using a many-ton hydraulic press. They don't just sort of sit there!

The usual thing with Type IV engines is that the interference fit is too slack, meaning the seats have a tendency to fall out, and the usual cure for this is to pull the old ones out and find/make some very slightly wider ones, and press them in.

With that head, if it really got to that point and someone decided to repair it, if the bore for the seat was too deep, you would cut a correct-depth slightly wider bore (resulting in a step between them) and then use an oversize seat and press it down to the step. But nobody really does that anymore, apart from on hand-build performance engines, since unless you have a machine shop its easier/cheaper to buy a new head.

Also I just thought of something. If a valve sits deeper then it should, wouldn't that mess up rocker geometry? Maybe that's whats causing all the clatter?

 

just a thought Adi as i wondered whether it would stand up to the temperatures its prob new head time for him then

 

If the 'low' seat looks to be solid and not loose it could as others have said either have been like that from the factory or have been re-cut at one time. If it were mine I'd get the other seats in that head re-cut by a local engineering firm until the valve drops were the same and all the valve stems were even height (assuming all the valves are the same length).

The tapping noise could be a worn cam or cam follower.

 

Agree with Adi - if the valve is sitting lower then the geometry is out compared to the rest of the valves. The valve guide could be wearing away and you can't see that unless you pull the head.

When my T4 had a valve guide that wore prematurely, the valvetrain became pretty noisy. Didn't affect performance much - the only tell tale sign was the sudden increase in oil consumption (and the noise ).

 

I already know what you guys are going to say in response to this - but to improve the valve to rocker geometry could I nip off a mm or two off the top of the valve stem? Would'nt want the collet to ping off though!

Im going to run up the engine tonight and use an engineering stethoscope to figure out where the noise is coming from.

Would it be possible to remove the plugs, left hand rocker gear and left hand pushrods and turn the engine over on the starter to see if it is the valve train on the left hand side?

 

Its up to you how you do it, all I can suggest is what I would personally do, which is to take the engine out and take the head off. It will take about a day max, and when it comes to top end troubles, its definitely a case of better safe then sorry. Remember, its possible for a dropped valve to destroy the whole engine.

The area where the collets sit is usually under considerable pressure, and it is therefore not so advisable to take any material from the valve stem top. It is however possible to change the length of pushrod, as is done on modified engines. The push rod is just a tube with two ends pressed into it, you can remove the ends if you are very careful and either cut the tube, or get a longer one and cut it to size, and then press the ends back in.

I remember seeing in a very old VW factory/service center manual that there is such a thing as a push-on repair cap that you fit to the tops of worn valve stems in order to extend their service life, to bring them back to acceptable height.

While you have the opposite, you need LESS valve stem height rather then more, it does however suggest that it is indeed possible for a valve to maintain function once a little material has been removed from the top of the stem. However I think this practice has long since died out, probably because new valves are cheap and top end failure is very expensive, and I have never done it or seen it done, so I do not know how long-lasting it is.

However, this would be a case of masking one problem with another problem.

Changing valve seats is not hard and does not take long as long as you have the correct equipment, and if a valve seat does not sit tight it does NOT have to mean a new head, since you can just make a valve seat that's a little bigger, and is of the correct size to sit in the head.

It is amazing how quick just a little sideways thrust can eat a valve guide. The valves are hardened steel, and the guides are bush-bronze. As soon as you upset the rocker geometry by even a fraction of a degree, that means the thrust on the valve is no longer straight vertical, and there is now a horizontal component to that thrust, and with this the hardened steel valve will eat the guide at an alarming rate, and will eventually probably mis-seat or overheat and drop the valve and make a big mess.

 

Wow Adi nice reply, thanks
I didn't have time last night but before I go ahead daking the darned thing apart again i've got to pinpoint exactly where in the engine the sound is coming from, if it is indeed the cylinder head then its not that much of a problem, as I have a spare one donated by a friend. If its a small end thats gone its a bit more work but do-able. If its a bottom end issue though I am really not going to be at all happy!

I was thinking of getting the old head re-seated, but to be honest you can still pick up 1200 heads for peanuts, so i'm not so worried

Will re-post when I know more.

 

Hi all, thanks for all the advice the problem is now fixed! (whoop whoop)
I took the rocker gear off the right head, there was a rubber O ring on the right stud but not the left. This caused the rocker to be canted slightly on the head. This meant that when the valves were set on the bench before fitting of the engine, the inlet and outlet for Cyl 2 were completely out, about 2 or 3 mm clearance!
When sorted though all sounds fine. There is still the issue of the sunken seat on Cyl 1 exhaust, but thats a job for another day