3,5 MK4-ticking noise only when engine is hot and over 1400 rpm

(Helmut) #1

Some month ago I bought a wonderful MK IV Saloon- 1948 with 3,5 litre engine. The car is in very good condition but has a Problem - when becomes hot (75-80 C) after 15min. beginns a “ticking” noise starting at 1400 rpm. More rpm faster “ticking”. It sounds like the valve clearance is too big but this is correct. Also the engine does not like to run too Long in slow traffic when the weather ist hot. The engine starts hot and cold very good and has much power. The engine was rebuilt some years ago but I do not know Details.
Is this “ticking” noise dangerous or normal - has somebody else had such Problems? Oil is 20/60 in the engine.
I hope you can understand my English but schooldays are Long ago.
greetings Helmut

(Peter Scott) #2

Helmut, Your English is excellent.

So the ticking follows engine revs. Can you say whether the noise becomes louder when put the engine under load. For example when running in top gear is it significantly louder when you accelerate?

Another little test might be to use an insulated screwdriver to short out the sparking plugs one at a time to determine whether any one cylinder shorted reduces the noise more than the others.

You could also use a long screwdriver as a stethoscope. Hold it firmly against the cylinder head and place your ear against the other end. Try this at various places and you might be able to determine whether the noise is louder at the front or the back or where ever.

If the noise is nearer the front then try running without the fan belt for a short test.


(Helmut) #3

Thank you for answer ! The noise becomes not louder when the engine is under load. It is the same noise starting at 1400 rpm and only when the engine is hot. When the engine is cold (first 15min.) the Sound ist like a new Mercedes perfect. I will try to put the sparking plugs short out.

(Peter Scott) #4

Try to assess where the noise is loudest. Back, front, left side, right side?


(Rob Reilly) #5

The screwdriver in the ear trick works great for finding the location of a noise, or you could invest in a mechanic’s stethoscope.

$13.88 at Walmart
My guess is if it is not bad valve clearances, it is a broken timing chain tensioner or a bad link in the chain.

(Graham Jordan) #6

Sounds like a valve guide that becomes loose when the engine is warm and hits the valve. If the engine was rebuilt it may have had K-liners fitted. This would make a definite ‘ticking’ noise.
Hope you find the issue.
Regards, Graham.

(Ed Nantes) #7

I’ve. Had a btacho cable make noise like that. Exasperated to ,isolate. Personally, I’d try isolating the easy stuff first
Is oil getting down all the pushrods? Were the rockers done?

(Helmut) #8

Thank you for so much Information. I ordered a mechanics and a electric stethoscope now and then I will try to find the place from where the noise Comes. The engine runs very good and there is no smoke and also the spark plugs look good. How does the Timing chain tensioner work ? Is the part where your finger is the spring which is important for the chain ? The pieces under the spring have no function like a spring - only that the chain slides comfortabel ?

(Ed Nantes) #9

Yes, you agre correct about The tensioner bronze fingers.
Could the noise be a cam follower. Do you know what, if anything, was done to them?

(Roger McWilliams) #10

All good ideas above. If tick is proportional to car speed but independent of what transmission gear is used, then tick source is somewhere along driveline at transmission output shaft or later, prop shaft, rear end, wheels and bearings, …, not in engine.

If tick is proportional to engine rpm regardless of transmission gear in use or in neutral, then tick source is in engine or item attached which rotates proportional to engine speed. External bits include generator, water pump, tach drive elements, clutch (including pedal linkage), distributor. Internal bits include rod and main bearings (which may sound more like a tap than a tick) and everything mentioned by others above. The engine can be run with the rocker cover off to observe the oil flow to all necessary bits, not too messy at low rpm.

A good starting point is to measure the cold valve clearances, put the rocker cover back on and warm up the engine, take the cover off again and watch the oil flow to all needed places. And what is the oil pressure at 40 mph (~ 60 kph) when engine is warm or very warm? If any rocker arms need clearance adjustment, be aware this is delicate on the adjusting screw and nut.

(Robin O'Connor) #11

Just make sure when using the non electronic stethoscope that you do not hit anything with the end, those things REALLY magnify the sound!

(Ed Nantes) #12

Yes , there should be a steady flow of oil running down the pushrods

(Helmut) #13

I am still waiting for my Stethoskop. In the meantime I looked at my rockershaft. I think there are different Systems with springs between the Rockers (=MY CAR) and other seen in the manuel with distance pieces between the Rockers. I see numbers on my Rockers C437 and C438. Everything Looks very clean and there is valve clearance but I heave not measured it exactly. In my Manual stand WARM tapped 0,12 inlet and 0,15 outlet. I do not see any Picture in the manuel from the Pushrod and from the tappet block. Is it easy to remove ?? Has somebody Pictures from the tappet block and the pushroads. I also see that there are different pushrod maybe in the cars - with a spring and a collar for the spring and without a spring ??? Is this possible ?
How does the pushrod fit in the tappet block ?
Maybe my Problem is in this parts.
Greetings from Austria

(Peter Scott) #14

If the valve guides are moving you don’t need a stethoscope. You will be able to see this with the rocker cover off.


(Graham Jordan) #15

Please Include some photos of your rocker shaft assembly. Forum members can then see if they see anything incorrect in the assembly.
Regards, Graham.

(jclucas@topspin.com.au) #16

Gents. I had a similar ticking sound in my 3.5l engine. It sounded very much like tappets and it wasn’t very loud, but it was at twice the frequency of the normal tappet tick. Adjusting tappets made no difference. I had a 3000 mile trip coming up so I pulled much of the engine apart and found the small end bush in one conrod was breaking up. I was getting one tick as the piston went up and a second tick on the way down. Replaced that bush, the noise disappeared and the car has done another 5000 miles tickless. Got to it just in time I reckon. I just hope Helmut’s tick has a simpler solution. Cheers, John Clucas

(Rob Reilly) #17

Perhaps this pic of my '38 2.5 with springs on the rockers is of interest.

My Mark V does not have these rocker springs.

Here is a tappet block in my Mark V.

You should get the parts catalogue if you are suspecting you have incorrect parts.

(Helmut) #18

Hallo Rob_Reilly!
This are very interessant Pictures - the Rockers are total different to mine. Your Rockers look like a “T” and have “spacers” . I think this is for reduce the noise of the rockers. My Rockers are like a “I” and look like in the Manual I have.
I also have a parts catalogue but there are no Pictures from the tappet blocks and also not from the push rods and springs…

(Helmut) #19

Now we had different tests with stethoscop and found that the noise is only from the rocker shaft. We put the rocker shaft off and hope that we found the Problem. One adjustable Ball-Pin in one Rocker is different to all other. This ball-pin is about 1 mm smaller than the others and has not a flat head - it does not fit good in the end of the push rod. The other ball-Pins fit very well and have no space. In my Manual I see that the push Rod in the 3,5 Litre has a spring with a collar on the end. My push rods do not have this spring. I can put all push rods out of the engine without a Problem. Is this normal ?? Does other owners of a 3,5 litre have also such a Version without springs?
Now I need new Ball-Pins with nuts. My push rods look good. Where can I buy this parts ? Is it possible to Change only the ball-pins without also Change the push rods ?

(Roger McWilliams) #20

Glad to hear you have identified a noise source.

Later engines had push rods which could be pulled out of engine. I’m not sure when that simplification happened, but it seems “T” and “Z” engines were this way and maybe “S” engines were not. Is there a mechanical reason to leave the earlier style collars in? Maybe others know.

For the parts need, once you get the ball pin removed, please identify which part of rocker assembly is bad. Each individual rocker assembly is comprised of rocker, felt wick, solder and pin, bronze bushings, ball pin, and nut. The ball pin, nut, and rocker threads for ball pin each could be damaged while rest of rocker assembly is okay. You may need another rocker in addition to the ball pin, and maybe also another nut. If you need another rocker, please specify which one is needed since there are two types on the engine.

Check the push rod for wear at place where wrong ball pin was working. If the push rod is identical to others (and look carefully inside pushrod cup) with correct ball pin, then no need to replace push rod.