Noisy CS 8/1

[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.

[38ac]

Does the knock get louder if you open the rack? Does it continue to knock if run up to speed and you close the rack? Does it knock if run up to speed, cut the fuel and decompress it?   Did you measure piston to cylinder clearance while it was apart? Have you checked the flywheels to see if they are loose? Look closely at the keys for signs of movement. Push and pull on flywheels to see if there is movement, check keys to see if they are tight.

[cobbadog]

Brilliant troubleshooting there 38ac

[silvertop]

Thanks for your input 38ac,
The knock is fairly consistent and gets a bit louder as the rack is opened and it continues to knock if the rack is closed but diminishes in volume. It disappears as the engine starts to die. The CS 8/1 is governed to 850rpm.  When I slow it to 650rpm the noise is still louder than my other CS Listers (governed to 650rpm) but not as loud as it is at 850rpm (I use a laser rev counter).

As mentioned earlier, the CS 8/1 does not have a compression change over valve.

Flywheels and keys are tight, this was one of the first things I checked. I subsequently removed the flywheels in order to remove the cam and check the cam / idler / crank timing marks and ensured flywheels / keys were tight when re-assembled. The CS 8/1 has the heavy flywheels, although slightly smaller diameter than the heavy flywheels on my CS 6/1. The concept of a flywheel coming off mid-flight and doing a high-velocity tour of my shed is something I prefer to avoid. When I slow the engine down the the knock clearly occurs just before the exhaust valve opens.

The bump clearance was checked as mentioned previously.

I have tried advancing and retarding the spill timing beyond the flywheel mark and it did not make any difference to the noise volume. The tappet and roller for the fuel pump appear to be in good condition with no sign of wear. I stripped the fuel pump and it is in good condition. The element looks to be good, as does the rack, and and all marks line up as they should.

I had considered that perhaps my hearing was becoming more sensitive with increasing age, but alas, this is not the case.

[silvertop]

I have been wondering if the valve seats are less recessed than they should be, but still sufficient to allow effective decompression when the push rod is lifted, and sufficient to avoid a piston valve interaction.
If the seats are less recessed than they should be this would reduce the bump volume even though the bump clearance is within specifications. I suppose a reduction in bump volume may lead to changed ignition and possibly a knock?

I note the manual advises valve heads must not be less than 1.39mm and not more than 2.54mm under the face of the cylinder head. I did not check this measurement on my engine.

I could test this by placing more paper 'shims' under the barrel, thereby increasing the bump clearance and bump volume. This may not happen for a while as I've just started to do a rebuild of my Lister HB2 engine.

Anyone else had a similar issue before? - comments welcome.

[gadget]

Have you tried a separate source for diesel? I would drain the tank and switch out the fuel from another station. You can't fully verify the fuel without some lab testing, just swap it all out and see.

I've gotten bad diesel fuel knock before...

[32 coupe]

"flywheel mark"

I would determine my own timing mark at this point.

Looks like you have covered everything else.

[gadget]

I had an 85 corolla diesel I was driving across three states a few years back. After coming over a grade I noticed the engine started to knock really loud. I had also fueled up right before the grade. Sounded like the bottom end was coming apart, I wasn't sure if I was going to make it. I thought climbing the hill killed it but it was just bad diesel. Next fill up the noise went away.

Turned out to be bad diesel. Probably had some gasoline mixed in it.

[silvertop]

Thanks for your input gadget,
This drum of diesel is fairly fresh. I fill the drums from the local fuel depot which is run by a major country-wide company. I use fuel from the same drum in numerous other engines as well as my vehicle and tractor without issue. The tractor and vehicle are both common rail which tends to be more sensitive to fuel quality.
This CS 8/1 engine has been fueled with diesel from different drums. I think it very unlikely fuel is the issue here.

[gadget]

I was hoping for an easy fix for you. If the valves where hitting the pistons, you would see marks on top of the pistons. Have you gone over it with a stethoscope yet? I know sound can travel and magnify in bell shapes but I would give it a go if you have one. You might be able to isolate the noise to a location.  I use one daily working on cars all these years. Also, how about posting a video with it running? Maybe someone here can recognize it. Bottom end noises are usually a deeper noise then valve train. Piston pin issues usually have a double clatter type noise. Piston slap and rod bearings can change during load transition but you really cant float/tap the throttle on this motor.

One other thought i had is timing gear backlash. though I think that rock back noise happens at over lap and not before exhaust valve opening. I don't even know if this motor has over lap...I guess its worth a look if you run out of ideas. Might be worth a try to load your flywheels with a 2x4, but is sounds like you've checked them thoroughly. Also, if you feel comfortable with this, try pushing down on the rocker above the push rod and make sure the lifter isn't sticking up a bit and getting slapped by the cam. You could probably actually check it with the motor not running.

Keep up posted on progress,  I'm pretty curious to see what it is.

[silvertop]

Cheers Gadget,
I would love an easy fix, but they rarely seem to come along. I looked for any marks on the top of the pistons potentially indicative of valve - piston contact, but there is nothing. Even with the exhaust valve decompressed there is nothing to indicate contact.

I don't have a stethoscope and my best efforts with a finger in one ear and my deaf ear up to the engine indicate the sound is coming from the upper barrel area - just where you would expect a diesel knock to come from. I have heard enough lower end; small end/gudgeon; and valve noises to discount these. Also, I have replaced the big end bearings, small end bushes, gudgeon pin, valve guides, valves, valve springs etc. As I mentioned earlier, these engines do not have any rings below the gudgeon pin, however, there does not appear to be significant piston wear. In addition, the bore still has some of its factory cross-hatch hone marks, even at the top of the bore (the bore is not chrome plated i.e. post 'Listard').

I don't know if backlash is likely to be an issue and I assume Lister made allowances for backlash in their gear design and placement. I suspect the level of engineering precision in these engines was perhaps a whisker or two less than that in Swiss watches. The timing gears and idler are in good condition with no appreciable wear.

The knocking noise occurs just before the exhaust valve opens so overlap can't be a contributing issue.

I also wondered if the push rods / tappets were perhaps hanging up and getting slapped by the cam, and this contributed to why I replaced the valve springs, however, both tappets and rods move freely and are well lubricated. The rollers in the tappets similarly work perfectly. I did remove the inspection door and look at the cam - tappet contact while turning the flywheels with the injector out and they work as they should without any hanging or slap.

As I suggested on yesterdays post, I'm now wondering about a reduced bump volume due to insufficient valve seat recess; or replaced valves that have a slightly different head shape / thickness. I imagine this could have a similar effect to carbon build in the upper cylinder or on top of the piston.