Lister CS6-1 Bump clearance

[Amp]

Rebuilding a newly aquired CS 6-1 after recovering it from an orange grove in Greece where it has been quietly rusting for about 40 years! It actuallly worked!! What is the bump clearance or deck height as some call it? My guess is that it should be set up with gaskets between cylinder and crank case so the piston is exacly level with the top of the cylinder, leaving the head gasket to provide the clearance. But I don't want to guess - hence this question

[buickanddeere]

  As close as possible without the piston whacking the head when the engine is warmed up and fully expanded.
  Some folk claim 20 to 40 thou cold works as a starting point depending.............................................

[billswan]

Amp

The clearance is called the bump clearance in the lister manual.

The reprinted manual I have says .045 to .50 thousandths of an inch.

Personally on my 10/1 oid I run it much closer.

Main thing is you don't get it so close that the valves hit the head.

Search this site for bump clearance and read for a couple hours, it has been discussed in length in old posts.

Welcome aboard the good ship LEF, AMP

Billswan

[Amp]

Many thanks for the info. Just so i understand what you're saying, does this clearance INCLUDE the head gasket thickness or is it a measurement of the piston top below the cylinder top face?

[Tom]

Yes. You can measure bump clearance by placing some soft solder or lead shot on each side of the piston above the wrist pin. Assemble and torque the head and then rotate the crank past TDC. Disassemble and measure the thickness of the lead shot.

[Amp]

Thanks Tom. One small concern; does this process mean I've wrecked a good new head gasket. Someone once told me that you can only torqu a head gasket down once. Will repeated removal and replacement make the seal iffy?

[lowspeedlife]

Hi Amp,
 Welcome to the board, since you have a real lister you likely have not done any harm to the gasket. your cylinder liner, if sleeved, is most likley the same height as the cylinder block. on the listeroids, that most of us have to deal with, the cylinder liner is always set too high to the cylinder block & usually compresses the gasket where the liner protrudes. If your engine does not have the removeable liner, or if it does not protrude above the cylinder block I would have no problem reusing it.
If you do need a gasket a member here "gaskets to go" has a good reputation & they make a gasket with a silicone bead on  it. if you prefer original style gaskets Stationary engine parts in the U.K. sells lister parts.

 Scott R.

[Amp]

Hi Scott,
Thanks for the info. The cylinder is genuine Lister I believe - no liner, just a solid lump and no evidence that the engine has ever been taken apart before. Your reply has put my mind at rest 'cos I can see myself taking the head and cylinder off and on at least twice to get the bump clearance right and I didn't want my workshop floor to be littered with new but un- reuseable head gaskets! Thanks once again.

[Tom]

According to some painting the gasket with aluminum spray paint will allow it to be reused many times. I haven't tried it my self.

[oliver90owner]

The original copper-asbestos-copper gaskets and the modern equivalents (no asbestos) are regarded as multi-use on a single pot block - many old cars with flat-heads used the same head gasket after the regular decarbonising sessions of that era.  They were spark ignition, not diesel, of course.  I would be very reticent to re-use a multicylinder head gasket on a diesel.

The newer composite gaskets available may not be quite so re-useable.  Sealing the fire ring might be OK but the cooling system, especially if any pressure is involved, might be a bear.  Also, not quite so sure about steel fire rings if fitted, either.

Also B&D said as close as possible - beware that the decompressor has to work with the engine rotating, so his comment you may lead you to come unstuck if the head has been trued up at any time by skimming.  Just be aware of it, that is all and take into account all operational factors.

Regards, RAB

Regards, RAB

[contaucreek]

Bump height= clearance between top of piston at TDC and the cylinder head when assembled and torqued.
Deck height=The difference between the piston at TDC and the top surface of the cylinder (adjusted by under cylinder paper gaskets)

[Stan]

  especially if any pressure is involved, might be a bear.  

Nope, no pressure involved.
Stan

[Amp]

Thanks for all the above . keep the comments coming - learning all the time

Amp

[oliver90owner]

Nope, no pressure involved.

Do you know that for sure, Stan?

Should not, but I do not know that for sure.  Could have had a rad change or any other mods since new.

Some are recommending the new composite gaskets for that very reason - they wish to pressurise the system.  Probably perfectly OK for first use but.......

Regards, RAB

[Tijean]

As mentioned in a previous post it is valve to piston clearance which is the critical issue more so than piston hitting head. Dont trust someones word that they used .0XX thou clearance  so that should be good in your engine.

How deep the valve seats are in the head, how thick the valve heads are and what valve lash clearance you use will all affect what the minimum bump clearance will be. Probably individual cam lobe profiles have slight differences too. The valve opening overlap near TDC on the exhaust stroke has the valves well off their seats when the piston is at the top.

With new heads and valves I would be very cautious about going with less than recommended clearances. Receeded and worn valves will tolerate less bump clearance but you are in uncharted waters.