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Lister ST3 about to fire up again! Or...?

The Stick Man

Registered
Hi everyone,
I hope you are all keeping safe, healthy & spending quality time with your loved ones during covid19.
I have found an opportunity to revisit my ST3 after putting other things first for quite a while. It has been a while since I posted something so I thought I would ask your opinion on a little something.

I rebuilt the engine which includes:
New oversized pistons & rings of course,
New valves & springs,
One brand new cylinder head,
New injectors and refurbished pumps,
Reclaimed the crankshaft on one main, new bearings & seals throughout.
I dialled in the head to piston clearance to within .001” of the minimum tolerance.

The motor turns over smoothly by crank and has good oil pressure. Once the decompression levers are shut. it can barely be turned over by hand due to the comp so I rebuilt the 2.4kw starter to turn it over for a start for the first time.

This is where my question & caution will become evident as I have spent a bit of coin & time in getting it this far after it was abandoned to rot.

When the decompression levers are activated it cranks fast and the only noise is the starter pinion meshing on the straight cut ring gear on the flywheel. It’s a lovely sound I have to say, but as soon as I shut the levers & have the compression resisting the rotation I have a slight knocking sound down low.
This is consistent and not a one off situation. I have repeated this about three times with the same result.

Now i know this will draw out a difference in opinion, but this is not a survey on identifying the reckless from the prudent. I could keep priming the system of fuel ignoring my spidey senses & when she starts cross my fingers all will be well. Having spun a few bearings on race engines in the past I know the pain and anguish that follows. I am very familiar with that distinct knocking sound, but this is not quite that loud (yet).

I am thinking of draining the oil and opening the side cover and budging the mains / rods to see if there is a little too much wiggle without tearing it all down again.

Is this a normal noise to hear whilst cranking due to the high compression or do you think I should tear it down & mic it up?

I just need some encouragement & wisdom here my friends.

Thanks
 

cobbadog

Registered
I feel your pain, time and effort. If it was me I would at the very least drain the oil remove the side covers and if you can double check for any movement. Something else that might help isolate the cylinder is to disconnect the joining rod of the decompression levers and only throw one in at a time to see if you can detect which cylinder is the offender. It will have the ability to start and run on one cylinder so be careful and have the fuel stop shut unless you do want it to start.
Tough decision to make but you have invested so much into the job and you dont want to stuff it up on a hope that it will not fail. I would be doing a thorough check.
 

mcmlvii

Subscriber
Last Subscription Date
04/17/2020
One thought about the knocking, each individual injection pump makes a *creak* noise when they go through their injection cycle. Could that possibly be the slight knock you hear? On second thought, you said that it only happens after the decomp levers are disengaged. The injector pump noise is present when the levers are engaged also, so nevermind.... Other than that, I don't have any enlightening thoughts. I do have an ST3 engine on my generator but I don't really notice a slight knock when cranking, although it usually starts with very little cranking so I don't have much time to notice anything.
 

The Stick Man

Registered
One thought about the knocking, each individual injection pump makes a *creak* noise when they go through their injection cycle. Could that possibly be the slight knock you hear? On second thought, you said that it only happens after the decomp levers are disengaged. The injector pump noise is present when the levers are engaged also, so nevermind.... Other than that, I don't have any enlightening thoughts. I do have an ST3 engine on my generator but I don't really notice a slight knock when cranking, although it usually starts with very little cranking so I don't have much time to notice anything.
No cream as it’s definitely down low.
 

The Stick Man

Registered
I feel your pain, time and effort. If it was me I would at the very least drain the oil remove the side covers and if you can double check for any movement. Something else that might help isolate the cylinder is to disconnect the joining rod of the decompression levers and only throw one in at a time to see if you can detect which cylinder is the offender. It will have the ability to start and run on one cylinder so be careful and have the fuel stop shut unless you do want it to start.
Tough decision to make but you have invested so much into the job and you dont want to stuff it up on a hope that it will not fail. I would be doing a thorough check.
Thx Cobbadog. I now have my answer. When in doubt don’t. She’s too nice to hurt after all that pampering. Satan is a crafty bugger and expert in tempting. Thx bud.
 

Oil Power

Registered
Backlash in the starter pinion when the cylinders go over compression? Piston slap from tight gudgeon bushes? I would be starting with caution.
 

The Stick Man

Registered
Hi everyone,
I hope you are all keeping safe, healthy & spending quality time with your loved ones during covid19.
I have found an opportunity to revisit my ST3 after putting other things first for quite a while. It has been a while since I posted something so I thought I would ask your opinion on a little something.

I rebuilt the engine which includes:
New oversized pistons & rings of course,
New valves & springs,
One brand new cylinder head,
New injectors and refurbished pumps,
Reclaimed the crankshaft on one main, new bearings & seals throughout.
I dialled in the head to piston clearance to within .001” of the minimum tolerance.

The motor turns over smoothly by crank and has good oil pressure. Once the decompression levers are shut. it can barely be turned over by hand due to the comp so I rebuilt the 2.4kw starter to turn it over for a start for the first time.

This is where my question & caution will become evident as I have spent a bit of coin & time in getting it this far after it was abandoned to rot.

When the decompression levers are activated it cranks fast and the only noise is the starter pinion meshing on the straight cut ring gear on the flywheel. It’s a lovely sound I have to say, but as soon as I shut the levers & have the compression resisting the rotation I have a slight knocking sound down low.
This is consistent and not a one off situation. I have repeated this about three times with the same result.

Now i know this will draw out a difference in opinion, but this is not a survey on identifying the reckless from the prudent. I could keep priming the system of fuel ignoring my spidey senses & when she starts cross my fingers all will be well. Having spun a few bearings on race engines in the past I know the pain and anguish that follows. I am very familiar with that distinct knocking sound, but this is not quite that loud (yet).

I am thinking of draining the oil and opening the side cover and budging the mains / rods to see if there is a little too much wiggle without tearing it all down again.

Is this a normal noise to hear whilst cranking due to the high compression or do you think I should tear it down & mic it up?

I just need some encouragement & wisdom here my friends.

Thanks
I drained the oil yesterday and opened up the side cover. There is no excessive play in the rods & it turns quietly and smooth. I tried to budge the mains with a lever on the crank with a similar result. I’m quietly confident it’s not a bearing issue at this stage. I think I’ll try and fire her up and see and monitor from there with my finger on the trigger so to speak.
 

denby

Registered
I've had couple of these but single cylinders and they are quite noisy. by memory they knock pretty well
 

cobbadog

Registered
Keep us informed and hope all goes well. I use a length of garden hose as a stephoscope to isolate noises, this might help.
Also after you start up and if there is still an issue decompress one cylinder at a time to see if that stop the knocking. If it does then that would indicate that one has a bearing issue.
 

rider5

Registered
Keep us informed and hope all goes well. I use a length of garden hose as a stephoscope to isolate noises, this might help.
Also after you start up and if there is still an issue decompress one cylinder at a time to see if that stop the knocking. If it does then that would indicate that one has a bearing issue.
Years ago I got an old stethoscope from the wife, I removed the end and slipped in a six inch length of copper tubing for a pick-up. Pressed against the metal it transmits localized sound very well and moved around near intake gaskets it allows me to hear even the smallest vacuum leaks. And I am still using it after some twenty five or so years.
 

gootsch

Registered
I use a long screwdriver with the handle pressed very firmly on the flap in front of my ear hole then the tip pressed on to the spot that I think that the problem may lie to find the source of those odd noises. I learned this trick many years ago, where I do not remember.
 

The Stick Man

Registered
I use a long screwdriver with the handle pressed very firmly on the flap in front of my ear hole then the tip pressed on to the spot that I think that the problem may lie to find the source of those odd noises. I learned this trick many years ago, where I do not remember.
Thx.
 

Combustor

Registered
Worked on a few ST-1 and ST-2 motors, mostly valves and injection work, then re-built a rather tired
ST-3. Was only for standby service, so it got new rings and the bores honed true, with piston clearance
close to upper limits. Started and ran fine, but hell, was it noisy! Has probably run several thousand hours since, still loud, but running fine. So if the noise can be localised to a little piston slap, I don't think it
should be a problem except to sensitive ears.Regards.
Combustor.
 
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