Hi Guys,

No doubt this topic has been done to death before.

I have just fitted a straight port head to my 3.4. I Took the opportunity to decoke the head and lap in all the valves. Compression is great @ between 155 & 160 per cylinder.
Used the same cams that came with the head.
All shims adjusted and clearances perfect at 4 thou. on the inlet side which is the problem area, somewhere near inlet valves 1 & 2.

There is a distinct tapping or knocking noise which is different from the usual valve chatter and I'm dammed if I know what the problems is. For some reason, the noise is not so prominent if the timing chain for the cams is not fully tensioned, but that only results in timing chain noise.

Any ideas would be gratefully received!.

PS The noise is occurs when the engine is accelerated more so when just idling, but overall there is no distinct pattern.

 

Depending on who did the last valve grind, if the seats were ground too deep and a thinner then normal custom shim had to be used to obtain the correct clearance, this may be your problem.
Because the shim is thinner, the top of the collar is now coming in contact with the underside of the lifter (the sound you're probably hearing).

If this in fact is what's happening, each time the cam opens the valve, the collar is essentially coming away from the "keepers" before the lifter comes in contact with the shim (this can also make noise).

If this is the situation, this must be corrected immediately, there is potential here that the valve stem keepers can come loose, allowing the valve to drop into the engine while it's running.

You don't have to remove the head to fix this.

Remove the cam shafts and follow the procedure as if you were adjusting the valve clearances so the time chain tensioners don't pop out.

Remove each lifter and look at the collar of each valve, they should be even or protruding above each shim.
Note that there is some leeway here, as inside the lifter, the part that comes in contact with the shim does have a slight shoulder on it.

However even with this, if the shim is too thin, the lifter may come in contact with the valve retaining collar before the shim.

The collar has to be removed and material must be ground off the collar to provide clearance.
One must be carful not to grind of too much, so as not to allow the adjustment shim not to be held in place.

There is a special tool to compress the valve, so the keepers and collars can be removed.
Compressed air is usually used to hold the valve(s) in place.

Personally I just turn the engine so the piston is at TDC on each respective cylinder and let the valves simply rest on the piston.
Great care must be used here not to turn the engine over while this procedure is being done.

I'm also assuming that you used the correct Jaguar tool to time properly align the cam shafts.

You also mentioned that the clearances are at 4 thou, the exhaust is at 6 thou. ??? The exhaust should be at 6 thou.

 

Hi Jeff,

Thanks for this very useful information.

Firstly, I should confess I did the valve grind. Probably should have left this to an expert, being a novice with the XK engine. But yes I used the correct timing "plate" to align the shafts. Set the exhausts @ 6 thou. and there seems to be no problems at all on the exhaust side.

I have since removed the inlet camshaft (must now be about the millionth time) and I now notice that there seems to be a gap between the top of the valve stems on cylinders 1 & 2 and the shim selected to get the 4 thou clearance.
I discovered this by putting a dob of paint on the underside of a brand new shim and replacing it in each collar - result, no paint on top of the valve stem. The remaining valves 3 to 6 indicate the shim is touching the top of the stem using the same test.

I realise now the shim MUST be in contact with the valve stem, otherwise the clearance measured will be totally false.

Your advice that the head does not have to come off is music to my ears. I will try your method of TD centering the pistons on cylinders 1 & 2, remove the collars and attempt to correct the faults.

Many thanks, I should sleep more peacefully tonite!

 

Don't drive it any more until this problem is corrected, there is a potential that an intake valve could drop into the combustion chamber.

Take caution when removing the collars and springs. Do each valve, one at a time on a given cylinder _ don't remove both _ finish correcting the problem on one and then move onto the other.
Remove all the spark plugs and after rotating the engine at TDC, block up the rear wheels so there is no chance the car can move forward or back.
The car should be in gear so the engine can't accidently rotate.

Here is what the tool likes like.

http://www.carid.com/images/lisle/au...ls/ls16550.jpg

USE LOTS OF RAGS SO THE KEEPERS DON'T ACCIDENTLY FALL DOWN INTO THE ENGINE

EDIT:
You're not going to like this, but you may have to remove the head, I don't think that spring compression tool will fit.
I don't think there is enough room to get it in place.

I suppose you could use a Dremel tool to grind away the necessary material off the collar _ one would have to be careful not to allow Dremel shaving to get all over _ lots of rags...

Just thinking, if the underside of the lifter is hitting the edge of the valve collar to obtain the correct clearance of 4 thou, then simply adding the correct shim to the top of the collar should correct the problem.

Another mistake people make is grinding the tip of the valve stem to obtain the correct clearance.
While you can do this, one mustn't grind too much off.
Grinding to much off will result in no contact of the stem to the shim.
If this is the case, the collar will have to be removed, put on a lathe and have material removed so the end of the valve stem protrudes above the collar.
The proper way to correct this is to get a new valve and or install a new seat.

You could probably could make something like this to compress the spring.
A "cut out" deep socket of the correct size could be used.

http://forums.vwvortex.com/showthrea...1#post64496383

 

Well, after a few anxious moments I managed to grind the inside of the valve spring collars just enough to restore contact between the shims and valves stems on intake vales #1 & #2 (the only culprits).

It took some doing. The collars are obviously made of very hard material (sintered steel?). Hopefully using the necessary precautions (rags stuffed down every orifice) no metal of grindstone material has entered the engine!

I used bearing blue to check contact btw. shims & valve stems. Upon reassembly after the usual repetitive shim selection process, I am happy to report the knocking noise has gone & valve train (after the obligatory chain tensioning) is nice & quiet.

Thanks to Jeff for his wise words of wisdom.

 

That is great- congratulations!

 

Well I'm glad you didn't have to remove the head and everything is working as it should !
Many years ago now, I had the valves done at a professional machine and they made the same mistake.
Luckily I checked it before it went back in.
The owner of the machine shop had this kid do it and he obviously didn't know what he was doing.

 

just to add an option, you could have also used a top hat shim, these are often used on MK2 race engines that the guy that machined my 3.4 engine builds. Saves a bunch of work if the seats are too deep.