How to / DIY > Engines

Noisy CS 8/1

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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...

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