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Noisy CS 8/1

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silvertop:
Would appreciate help/comments on the following:
I have a Lister CS 8/1 (Made in England; not Listeroid). It runs noisy with a pronounced 'diesel knock-like' sound, more pronounced than my other CS Listers. I sounds similar to one of my air-cooled Listers.

I checked the timing, and spill time, and reset the tappets, to no avail. I have replaced the big end bearing, small end bearing, gudgeon pin, rings, valve guides, valves, valve springs, and injector nozzle. The big and small-end bearings did not need replacing but I did it anyway just to eliminate them as a cause. I have serviced the injector and fuel pump. In addition I have run it with a fuel pump and injector off another CS 6/1 engine but the noise is still there. I checked and cleaned all linkages (including governor) and they all work as intended. I have checked the bump clearance with 2 small lead balls and adjusted to ensure it's within specks (1.9 - 2.03mm). This model has one oil scraper ring above the gudgeon, but there does not appear to be significant piston wear. I have run it as slow as I can and the 'knock' occurs just before the exhaust valve opens as might be expected with a typical 'diesel knock'.

Incidently, the engines starts and runs very well.

This is a 1978 Lister 8/1 (one of the latter English CS 8/1 Listers) and the barrel has recessed corners with the 4 studs on the outside rather than incorporated into the barrel as on almost all earlier CS Listers (the barrel is the original English Lister barrel and still has the factory hone cross-hatch). Could this different shape of the barrel with the 4 studs on the outside be contributing to the 'knock' sound? Has anyone else had a similar experience?
Alternatively, is there something I may have missed?

mike90045:
have you scraped carbon off piston & head ?

  Try some water injection after it's well warmed up

does it have a cold start valve/chamber that's stuck in starting  (high compression) setting

Any chance that parts (head) got swapped for the wrong kind ?

Is the fuel "good" ?  not thinned with gasoline or kero ?

Just some wild guesses from outside the box

silvertop:
Thanks for the comments Mike.
All parts of the engine were cleaned including all parts of the head and piston. There wasn't much in the way of carbon build-up prior to cleaning anyway.
 
The CS 8/1 engines do not have a compression change over system. There is a plug where the compression change over valve would normally screw in and it appears the CS 8/1 only operates in what would be the higher compression mode of the CS 6/1. I haven't attempted to remove the plug, although the injection chamber has been pressure cleaned and does not appear to have any build-up.
 
I'm sure the head is original. I have the original manual and parts list that came with the engine. The previous owner also gave me the service record notes from since the engine was new and there is no mention of changing the head. Apart from the absence of the compression change-over valve, heads for the 6/1 and 8/1 appear to be identical. Incidentally, the CS 8/1 uses a tappet clearance of 0.20mm for both the exhaust and inlet valves compared to the 0.43mm (Inlet) and 0.82mm (exhaust) tappet clearances for the 6/1.

Fuel and oil are new. The fuel tank and fuel filter are also new. The CS 8/1 engines have a Delco 296 cartridge-type fuel filter compared to the old 'filter wick' of the CS 6/1 engine. I buy fuel in 205 litre drums and use the same fuel in all my diesel engines without issue. I use Penrite HPR Diesel10 10w-40 semisynthetic oil in all my diesel engines and they seem to like it.

There must be something I have missed that is causing the engine to make this 'knock' sound and hopefully someone will point out the "obvious".

Cheers

cobbadog:
Sounds as if you have been thorough. Interesting about the vast difference in tappet gaps between the 6 and the 8. Next and it is clutching at straws but I would drop the synthetic oil and run SAE30 nstandard oil as recomended for these engines. If not available a straight 15W/30 will do. These are old style engines and some reject the modern oils. I run Gulf Western in the tractors, truck, McDonald diesel and the Lister

BruceM:
An interesting situation, silvertop.  You have covered all the obvious causes competently.  Unless 38AC pitches with an answer, I'd probably accept that there is a volume issue with the head and just add some gasket spacers under the cylinder to get the knock down to normal. If that works, it is self validating.

Flywheel to key play has occasionally be reported as a knock source; that's the only other thing I can recall that you didn't specifically cover already.

As 38AC has shared with us in the past, even Lister CS's have occasionally had  QC and consistency issues.

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