Chasing a suspicious engine knock.

[rleonard]

I have been concerned about an every-other-revolution knock on my freshly rebuilt  Lister 6-1.  I checked the obvious; valve clearances at TDC, and felt the flywheels carefully when turning by hand for any hint of an interferance.  There is no noise when turning slowly or rapidly by hand.  Either on compression or decompressed.  Once it is running over about 200 RPM, there is a knock that just does not sound right.  It is independant of rack position and engine load.  The origination seems to be in the head.

I went ahead and pulled the head tonight.  All is in order.  There is a slight pattern in the carbon around the intake valve on the piston but it must be from the flow pattern.  There is no evidence of interferance or contact whatsoever. 

I checked bump clearance.  Spec is .045 to .055.  I measured .0445 and .045 with each pieces of solder over the wrist pin just as specified in the Lister engine manual.  There is no interferance with the piston and the head gasket.

The engine has a fresh piston, rings, wrist pin and bushing, and lower rod bearings.  Rod to crankshaft clearance is .002.

Any other place I should look?   The cam and valve train is as quiet as can be.

Bob

[MacGyver]

Does it make the noise on coast down from speed (with the fuel off), or only when it's injecting fuel and firing?

[Tom]

I see you are in America so you probably have a riod. Check the lash on your cam gears. They tend to slap around after the follower for the IP goes over to the back side of the cam lobe. Mine was noisy like this until I installed a bronze idler gear and one of xyzer's off set idler boltes. Now it is much quieter.

[Stan]

Rod to Crank clearance of 0.002 is good.  Did you measure all around the crank with plastigauge or just in one longitudinal strip?  Did you check the nip, (interference between the bearing and the bore of the connecting rod)?  It should be between 0.004" and 0.006".
Stan

btw....nip is an old english term for how the bushing fits on to the big end of the rod without the crank in place, not an inappropriate and politically incorrect racial slur.

[rleonard]

Thanks for the replies.

As I said; "It is independant of rack position and engine load"  It depends on engine speed only (over about 200 rpm) and does not change with the acceleration or coasting.

This is a English Lister.  The real thing.  It really sounds like the piston hitting the head.  That is why I checked the bump clearance and closely inspected the head gasket.

There is no interferance that I can find and the gear train sounds quiet.  I'll reach in and check the gears again though. 

Bob

[rleonard]

Rod to Crank clearance of 0.002 is good.  Did you measure all around the crank with plastigauge or just in one longitudinal strip?  Did you check the nip, (interference between the bearing and the bore of the connecting rod)?  It should be between 0.004" and 0.006".
Stan

btw....nip is an old english term for how the bushing fits on to the big end of the rod without the crank in place, not an inappropriate and politically incorrect racial slur.

I was using micrometer and bore gauge.

I thought a nip was a small quantity of liquor...

[Stan]

You put the big end together complete with bushings, but without the crankshaft,  tighten it up to spec, then back on nut off fully and check the resulting gap at the parting line in the other side. 
Stan

I always thought it was something a puppy did to you.

[rleonard]

Ahaa yes that to.  Also cutting a small piece of metal, with a shearing device.

LOL.  Thanks,

Bob

[rcavictim]

It is also a property aquired by air when it gets cold.

[MacGyver]

It is also a property aquired by air when it gets cold.

Which makes certain body parts rather pointy...
Hence the phrase "My,  It's a little nippley out isn't it?

[oliver90owner]

Bob,

Have you checked that your flywheels are tight?

Regards, RAB

[rleonard]

Good suggestion RAB.  I'll check the gib keys tonight.  The head is still off.  I'll put it back on tonight too.

Bob

[biobill]

Bob,
  If the noise is heard on every other revolution, pull the big inspection cover and watch the cam, gov. assy,  and idler gear as you rotate the engine.  What I thought was a rod knock on mine was actually the idler gear hitting the side of the crankcase when the exhaust lobe overcentered.

[rleonard]

Thank you BioBill.  I'll take a closer inspection of the gear train.

Bob

[oliver90owner]

Bob,

Is the big end bearing shimmed?  If so remove and check for tightness of bearing It should be tight on the crank without the shims, I would think.  If it is still loose then you possibly have too much clearance on the big end. 

I scraped in my bearing 'cos it had been run without a dipper (I think). I scraped it until just slightly tight with minimum shims and then shimmed for clearance.  Spec says free but not more than 3 thou. Mine is certainly less than 3 thou and when it is worked with a vengeance, I will recheck and re-shim as necessary as this was my first scraping experience.

Things like did you check for ovality on the crank journal, come to mind.  On mine the dipper threads prevent any temptation for the bearing inserts to move round.  Other things to look at are timing and fuel type, along with injector operation.

Regards, RAB