could be a faulty rocker arm or even a worn cam follower

 

could be a faulty rocker arm or even a worn cam follower

And that would only make the tapping sound after engine warms up? And mostly audible from one side of engine?

How do I track that down?

 

It could also be an exhaust leak from the manifold. When it gets warm, it expands, making the leak larger. That would give you the knocking sound.

One way to find out is to suck a can of Seafoam into the intake. Not only will it clean out the inside of your engine, but it will smoke like crazy. This helps pinpoint exhaust leaks, as well as annoy your neighbors.

 

Thanks Skip, seafoam it is. The more it annoys my neighbor across the street the better.

I'm confused about the whole coolant system under pressure thing though. I've called 2 mechanics today and didn't really get an answer to my how/why questions that satisfied me.

The coolant system is under pressure, more so while engine is running. When engine warms up thermostat opens and coolant flows from tank into system. When engine cools coolant flows back into reservoir. What prevents *significant* amounts of coolant form flowing back into the tank? My tank looks like it is very low until I open it up, then it fills as pressure (vacuum?) is released. It didn't do this before, I wish I could pin-point the time it started doing this but I cannot.

 

1. Put a compression gauge on a cylinder
2. Using a socket on the alternator, rotate the motor until peak compression
3. Screw in a fitting that lets you pressurize the cylinder with compressed air
4. Ensure radiator expansion tank is full to the brim (fill with water or water/coolant mix). Leave cap off
5. Pressurize the cylinder (they are designed to take more than 100PSI each stroke so it is OK)
6. If there are bubbles, you have a problem.
7. Repeat
If you find you get a volcano out the tank, you know you have a bad example of a slipped liner.

 

Greg. Are you saying that if air bubbles it could be a headgasket or liner but if lots of air bubbles then a liner issue most likely.

 

Great advice, thanks Greg. Looks like I need to go shopping for a few tools/fittings.

 

you can get a test to see if there is exhaust gasses in the coolant

 

you can get a test to see if there is exhaust gasses in the coolant

We tested my car for that several times and got no result. It did have a slipped liner.

 

Testing for exhaust gases in the coolant is mainly for head gaskets. That is the compression of the cylinder forces the gases into the coolant system. It may not show up a slipped liner.

Not sure how your coolant system is staying pressurised when cold. But probably more of an indicator of a head gasket rather than liner.

Tapping noise from the motor is usually a tappet rather than a liner.

An easy way to track down where a noise is coming from is to simply use a bit of garden hose a couple of feet long. Shove one end to your ear and move the other end around various parts of the motor until the noise is loudest. Also a good way to find exhaust leaks.

 

Either way, you have to take it to bits if the cooling system is pressurized when cold.

If you do my test, you may be able to narrow it down to which cylinder is at fault. This gives two benefits.

1. you know exactly where to look for the leak. If there is no problem with the head gasket in that area it has to be a slipped liner.
2. If the problem is only on one side, you only have to take one head off not two to do the inspection.

Be aware that a slipped liner can stop in the right place and look fine. It may also be out by just 1mm but that is enough. You can feel it with a finger nail in mine.

 

From my experience of a "tapping" engine when warm / hot and occasional water pressure (blown throttle body gasket, leaking heater O ring, and pressure in the reservoir occasionally), It can be a total waste of time and money trying to cure the fault. I stripped and inspected my engine. There "might" have been a very small mark on the Right Side Head Gasket - hard to tell! I replaced both rocker shafts, all rockers and hydraulic tappets and had the heads checked and skimmed to no avail. Still knocked when warm.
The car was in daily use covering 100 miles a day and drove as it should do. Just the loud tapping below 900rpm.

Bit the bullet and fitted a Cosworth engine. That was 9000 miles ago. No tapping, NO water added and 30% increase in economy!

The block was blueprinted to check liner alignment and verified ok. The liner / liners would only move at low rpm when warm and just happened to return to the correct position when I stripped the motor.

Speaking to an engineer at RPi, I was told this was exactly what happens to these engines. No quick fix as the problem is caused by a crack in the water gallery wall between two cylinders due to insufficient thickness AND over temperature.

The most likely cause in my case was a silted up radiator. No over temperature was indicated. I carried out a water capacity check compared to a genuine replacement unit and found that the rad was 30% clogged (IIRC) with reduced flow rate.

Does anyone need heads, or rocker shafts or rockers ..............

Ray

 

So I sucked a can of Seafoam into the intake today. Mucho smoke, however no clear leak in hte exhaust or manifold. I did see a few whiffs of smoke on the LH side of engine, but they seemed to be coming from nowhere.

However I have somewhat localized the mystery sound I think. While I was underneath looking for smoke leaks the wife was revving the engine a little. When the engine is idling and one quickly hits the accelerator there is a loudish sharp SNAP sound, like a small firecracker perhaps, or a whip crack. It is difficult to describe this sound, I made this recording while laying under the vehicle holding my cellphone up towards the LH side manifold, where it seemed to be coming from. It really sounds nothing like it does in real life though.

Now I'm waiting for some new tools to be delivered from harborfreight...