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sheldricka

Unspecified engine knock

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Does anyone have a view on the source of this knock, its there from starting, quiet at low revs once started and get louder when hot and follows the engine speed. Its not coming from tappets, all set for a standard cam, oil pressure is also good, compression is also good on all cylinders. The noise is high up towards the front two cylinders. Using a stethoscope its detectable but not on any specific point. Ive recently replaced the cam followers as some were tight in the block, ive also had the first two pistons out to inspected the small ends. All thought welcome. Video attached.

CA47E118-3374-43CA-8146-DC288F7024D3.MOV

Edited by sheldricka

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What was the condition on the followers faces. If anything other than perfect I would consider the cam for removal.

 

Roger

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They werent too bad but not perfect, a couple were mushroomed and took some persuading to get out. No2 was one of them

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If the tappets were damaged it would be best to inspect the camshaft too.

Compare all lobes, especially those that had worn tappets with the rest.

Regards,

Waldi

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Thanks Waldi, Ive been suspecting the cam, just wanted some other opinions before I take on the effort to strip it all down. Alan

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Have you tried rocking/turning the engine by hand to try and better pinpoint the source?

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Hi Mike, only when setting the valve clearances and its only noticeable when its running

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Alan,

If you would have very worn lobes, you could measure the (reduced) maximum lift with a micro meter once you have removed the rockershaft.

Good luck,

Waldi

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Yes Ill give that a go, just mustering up the enthusiasm to take it out, I might pull the whole lot out and check it all over while Im at it. Probably easier in the end.

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Have you tried running the engine with the fan belt off to eliminate water pump and alternator from the equation?

Edited by Steves_TR6

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Hi, yes, no change. Its definitely coming from the upper block area. Thanks for your suggestion. Alan

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Alan,

Since a couple of tappets were mushroomed, the cam and followers are a very likely spot to look at.

Engine out makes work easier and gives a better quality, choises, choises, choises.

Waldi

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Thought Id provide an update since the engine is out, stripped and has been inspected. It would appear from the analysis that at sometime in the past the block may have been skimmed, at TDC the pistons are 28 thou ish out of the block causing number 1 in particular to hit the head. This only manifested itself when I changed the head gasket to a Payen one which when compressed is around this depth. Plan now is to fit a thicker copper gasket to solve this issue. Pictures attached, all other components checked and found to be undamaged and in spec. This problem was not a problem before the head gasket was changed out!

post-14393-0-84045400-1535995060_thumb.jpeg

post-14393-0-85363500-1535995075_thumb.jpeg

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Since you have the engine out and stripped, have you considered having it "zero decked"? You wouldn't have the expense of replacing a copper gasket each time you remove the cyl head.

 

I had my block & pistons zero-decked accounting for around 0.030" Payen head gasket when compressed.

 

Richard.

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Alan,

Good you found the cause.

Check the upper part of the piston for deformation.

Use a feeler gauge and compare the vertical clearance between the piston and the upper ring, after cleaning piston and ring.

The clearance should be even around the circumference

If deformed, you have to make the call: replace or not...

Think I would, since fatigue is a future possibility due to the combustion forces once the material has some very small cracks. Others may have hand-on experience.

Waldi

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Yes sound advice from both of you. Now I have the bits back Im going to complete a dry build and measure up to determine the best next step.

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They werent too bad but not perfect, a couple were mushroomed and took some persuading to get out. No2 was one of them

Unfortunately if any of the cam followers were mushroomed it means that the camshaft is knacked, as indicated by Roger. I would also check the valve springs to see if they are too heavily rated ones, as using this type is well known to mushroom the cam followers and knock out the camshaft?

 

Bruce.

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Hi Bruce, yes, I’m havimg the head refurbished as part of this process, I currently have red stripe springs which I believe are standard. As well as this ive ordered a Newman cam and followers and will be putting in a custom thrust washer set in as part of the overall engine refresh.

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To get the engine zero-decked you'll be needing to skim the pistons by up to 0.028" by the sound of it. This is a reasonable amount, but you probably don't need to go that far. I actually chose to run my 2L 6 at 0.005" pop-up. This partly to gain compression (head is a heavily modified 2.5 one and has already had a huge skim) and partly to gain a bit of extra squish.

 

I would agree that the cam needs very careful checking and also the valve springs. The follower faces also need to be checked for flatness (they should be dead flat) as there are still suppliers out there (who should known better) who seem to think that crowned tappets are ok in Triumph engines. They are not.

 

Nick

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Some years ago at a big international meeting one of the lads from Revington said Hi Peter your followers have gone. Hum, how the hell does he know? I have been chasing this knock for 2 years, stethoscopes and everything. No experts could tell what was happening. So I ask him how did he come to this conclusion? Easy, you can hear the knocking at the front end and at the top half of the engine. It is a Triumph weakness the cam followers always go at the front end of the engines. 2 years later when the engine was stripped dow, we found the front followers were pitted badly, just as he said. End of story.;

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