Top end tappety type noise

[bobfather]

Boosted LS1 said:

^ This has me a bit confused. Won't there be a few inlet valves open?

If the exhaust valves are open the inlet valves will be closed. If the inlet valves are open the exhaust valves will be closed. There will never be a time when there's an open route from the tail pipe to the air filter

[blaze_away]

I will try that too sounds interesting

[Dominic TVRetto]

Is that not what cam overlap is..?

[Boosted LS1]

Dominic TVRetto said:

Is that not what cam overlap is..?

Yes, hence my confusion with the method.

Edited by Boosted LS1 on Tuesday 26th February 08:54

[blaze_away]

Update

Bottle of Wynns Hydraulic Lifter Treatment added and 10 miles driven. I think its quieter but too early to tell needs more miles

[DickyC]

blaze_away said:

Update

Bottle of Wynns Hydraulic Lifter Treatment added and 10 miles driven. I think its quieter but too early to tell needs more miles

The reviews are mostly good but folk are talking about longish runs or several days of short runs to make a difference. The negative comments are so strident the noise probably wasn't tappets.

[ChimpOnGas]

bobfather said:

Boosted LS1 said:

^ This has me a bit confused. Won't there be a few inlet valves open?

If the exhaust valves are open the inlet valves will be closed. If the inlet valves are open the exhaust valves will be closed. There will never be a time when there's an open route from the tail pipe to the air filter

Not true

Let's study and understand what is really going one here

1. If the exhaust valve is shut your applied pressure up the tailpipe is going nowhere, other than out of any unwanted path to atmosphere (an exhaust leak).

2. If the exhaust valve on a cylinder is open but the inlet valve is shut, the effect will be the same as point 1 but you will also be applying pressure to the combustion chamber on that cylinder. Any loss of pressure could therefore be an exhaust leak in the same way as shown by point 1, but it could also be anything that dictates the sealing of that combustion chamber, examples being inlet valve to seat seal, valve guides, piston rings and bore condition.

3. However, if the exhaust valve is open on a specific cylinder at the same time as it's inlet valve, any reverse pressure applied up the tail pipe will pass the open exhaust valve into the combustion chamber, then straight out past the open inlet valve into the inlet manifold. You may assume the inlet manifold is sealed at the throttle but this is not the case as there is always an air gap between the throttle body and the edge of the throttle butterfly, the inlet manifold is also directly connected to the crankcase with no valve.

The valve timing event where both exhaust and inlet valves are open at the same time is known as valve 'overlap', when you turn the ignition switch off on an 8 cylinder engine the probability of one of those 8 pistons coming to a rest when the valves above it are in the overlap condition is very very high.

With the above understood we can now see the practice of applying a reverse pressure to the tailpipe is strictly speaking an unreliable method for identifying an exhaust leak on all cylinders, even if you rotate the engine as soon as the cylinders on overlap are in a condition where both inlet and exhaust valve are firmly shut you're going to find other cylinders will be on overlap.

As the tail pipes are merged to one single exhaust pipe (between the silencer box and the 'Y' piece), any reverse pressure applied to either tailpipe will be shared across all 8 cylinders, and it's a certainty that some of those 8 cylinders will have valves on overlap proving the reverse pressure method for identifying an exhaust leak is fundamentally flawed and so a completely unreliable diagnostic method.

Feathers taped to pencils wouldn't be my choice either, what you need to do is far simpler and infinitely more reliable than trying to pump up the exhaust system or making a daft little wind detector out of your pet parrot. All you need is a length of fuel or garden hose, with the engine running put one end of it to your ear and pass the other end over areas likely to leak ie any joints but especially the exhaust manifold flanges where they seal at cylinder heads.

Trust me, using this simple listening method will soon have you locating any exhaust leak that may or may not be present at any specific point in the system. A running engine creates huge pressures which is why we often use it to turn a compressor (a turbo), this pressure is way stronger than anything you could ever hope to reverse apply up the tailpipe so it'll soon find it's way out to atmosphere through even the tiniest gap.

[bobfather]

ChimpOnGas said:

Not true

I bow to your greater knowledge sir....but, just to confirm

All eight cylinders have the same suck, squeeze, bang, blow sequence so let's take one cylinder as an example.

You are saying that there is a instance on every cam rotation that cylinder 1 will have both exhaust and inlet valves open. That is a surprise to me

[DickyC]

[phazed]

Unfortunately yes Bob.

That is why especially with a racier cam the overlap is greater and the engine will blow back into the plenum which is confirmed by the 'horrible state in the plenum when you would have thought that it would remain clean by just air whizzing through it.

A good enough reason to have throttle bodies!

[TV8]

I don't mind if they overlap or not but would love to see a pic of someone with a duct-taped exhaust and flexible tube trying to pressure test the system.

[Boosted LS1]

bobfather said:

ChimpOnGas said:

Not true

I bow to your greater knowledge sir....but, just to confirm

All eight cylinders have the same suck, squeeze, bang, blow sequence so let's take one cylinder as an example.

You are saying that there is a instance on every cam rotation that cylinder 1 will have both exhaust and inlet valves open. That is a surprise to me

Correct. It's called the overlap period which is when the inlet valve opens maybe 40 degrees before the exhaust valve has closed. During this period some of the inlet charge is used to purge the cylinder of exhaust gasses. If you google 'valve overlap period you'll find the info.

Edited by Boosted LS1 on Thursday 28th February 12:16

[bobfather]

TV8 said:

I don't mind if they overlap or not but would love to see a pic of someone with a duct-taped exhaust and flexible tube trying to pressure test the system.

My topic here, I successfully located a leak at the passenger side 4 into 1 weld using this method

http://www.chimaerapages.com/technical-info.html

[ianwayne]

ChimpOnGas said:

Feathers taped to pencils wouldn't be my choice either, what you need to do is far simpler and infinitely more reliable than trying to pump up the exhaust system or making a daft little wind detector out of your pet parrot....

I read that tip on here and can't bloody find it now. I didn't invent it, and it worked for me in identifying that on my last car it WAS the exhaust manifold gaskets leaking. The OP was asking for advice on how to establish whether or not he had tapping valve lifters or not.

Have you tried it? Thought not. We mostly all have a cushion or pillow somewhere with feathers in them. Quips about pet parrots are uncalled for.

[TV8]

bobfather said:

My topic here, I successfully located a leak at the passenger side 4 into 1 weld using this method

http://www.chimaerapages.com/technical-info.html

Great work, that looks more substantial than duct tape!

[Loubaruch]

ianwayne said:

I read that tip on here and can't bloody find it now. I didn't invent it, and it worked for me in identifying that on my last car it WAS the exhaust manifold gaskets leaking. The OP was asking for advice on how to establish whether or not he had tapping valve lifters or not.

Have you tried it? Thought not. We mostly all have a cushion or pillow somewhere with feathers in them. Quips about pet parrots are uncalled for.

Ian take no notice of COG, I rarely do, a feather or preferably some goose down on a piece of dowel I have also found to be a very good way of detecting gasket leaks provided of course that the cooling fans are not running.


www.bertram-hill.com

[ChimpOnGas]

Loubaruch said:

ianwayne said:

I read that tip on here and can't bloody find it now. I didn't invent it, and it worked for me in identifying that on my last car it WAS the exhaust manifold gaskets leaking. The OP was asking for advice on how to establish whether or not he had tapping valve lifters or not.

Have you tried it? Thought not. We mostly all have a cushion or pillow somewhere with feathers in them. Quips about pet parrots are uncalled for.

Ian take no notice of COG, I rarely do, a feather or preferably some goose down on a piece of dowel I have also found to be a very good way of detecting gasket leaks provided of course that the cooling fans are not running.

www.bertram-hill.com

• Listening sticks and stethoscopes are the way to detect and isolate mechanical noises

• Vacuum leaks are detected with either a can of easy start sprayed at a suspect area, however a hose pipe used as a crude ear trumpet is far safer and very effective

• The hose pipe listening method works equally well for exhaust leaks

• Smoke testers are also used for identifying leaks on modern engines that are typically far better sealed

• Feathers are for birds, pillows and puffa jackets, they are are not really engine bay friendly, rad fans blow a lot of air and exhaust manifolds get very hot

A simple length of garden hose used as a listening device is how I was trained by those who made their living from such things, and how these old boys who taught me were trained by those before them.

Put away your butt plugs and give poor Polly a break too!



If we've got people who don't even understand the concept of valve overlap offering flawed diagnostic methods, there's little hope for the average Joe who just comes on here for some reliable tried and trusted advice.

[ChimpOnGas]

Boosted LS1 said:

Correct. It's called the overlap period which is when the inlet valve opens maybe 40 degrees before the exhaust valve has closed. During this period some of the inlet charge is used to purge the cylinder of exhaust gasses. If you google 'valve overlap period you'll find the info.

Edited by Boosted LS1 on Thursday 28th February 12:16

^^This^^

An educated voice of reason at last!

[Squirrelofwoe]

TV8 said:

I don't mind if they overlap or not but would love to see a pic of someone with a duct-taped exhaust and flexible tube trying to pressure test the system.

I did this but I don't think I took any pictures! I used two tennis balls (perfect sized bung for a Chimaera tailpipe), one with a tube inserted through it hooked up to a compressor, with a spot of duct tape to ensure a good seal.

Few seconds of pressure from the compressor and any exhaust leaks are clear as day.

It did get some funny looks from the neighbours

Unfortunately for me it wasn't a manifold gasket leak causing my ticking

[bobfather]

ChimpOnGas said:

Put away your butt plugs and give poor Polly a break too!

Nowt wrong with butt plugs, I've had two exhaust leaks many years apart and both were located both using this method. Air supply to the tail pipes and a bottle of soapy water around the suspected areas. First leak was at a 4 into 1, the second was manifold gasket failure. Both were quickly found by the appearance of bubbles. Simple, quick and accurate

Edited by bobfather on Thursday 28th February 15:09