How to / DIY > Engines

Noisy CS 8/1

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dkmc:

X3 regarding 38ac

Also, I'd like to hear more as to piston clearance.....as below.


--- Quote from: silvertop on January 06, 2021, 10:59:11 PM ---I don't have a measurement for the piston - cylinder gap on the CS 8/1. Do you have any guidance on this?
Are aluminum pistons on the CS engines thought to wear faster than on other engines?

--- End quote ---

38ac:
Below are the sizes and clearances as per the technical data sheets. It is important to know that standard practice at Lister was to machine clearances into O.D. of fitted parts not the I.D of a bore. Example the CS cylinder bore is 4 1/2". To provide the needed operating clearance the piston is made smaller than 4 1/2" not the bore bigger, get it?
lister CS bore is 4 1/2" machining   tolorances are -000 to +.002
Cast iron piston is a 4 1/2" with a machining tolorances of -.005 to -.0065
Aluminum piston is also 4 1/2" with machining tolorance of -.007 to .008.
 Maximum allowable cylinder wear is .004
Maximum allowable  piston wear is .005
What that means is if the wear is less than stated the parts are good to out back in service.

So,,do the math an aluminum piston 8/1 can have anywhere from .007 to .010 clearance and be in new engine specs. When you add in maximum allowable cylinder and piston wear. The maximum allowable clearance is .019" and that is pretty doggone loose and will make noise.

MachineNLectricMan:
While this topic has aged a little, I'll add my 2 cents. Piston "slap" is a common annoyance in many types of aluminum piston engines. I have an 8/1 and the slap go's away after it warms up. The extra clearance is to allow for more skirt expansion as the engine gets hot, but is annoying in a cold engine. Also the engine may have excessive piston clearance even for aluminum. The noise can be unnerving and sometimes will cause a person to mistakenly look for a serious engine problem that doesn't actually exist. Better to be safe than sorry though.

You can actually knurl piston skirts, or hand stipple them to decrease the clearance. This actually causes more oil to be retained on the piston skirt too. This was an old race engine building trick in the older days. There is a proper way to do this though, so let a machine shop do this.

mihit:
In place of a stethoscope, the handle of a screwdriver can be held up to your ear or temple, with the blade pushed against parts... obviously this only works when you don't have to put your head in the flywheels!

cobbadog:
I also use a short lngth of garden hose if the long screw driver isn't handy.

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