Hi there
Just put my cylinder head back on.

i turned the engine with my hand on the engine sprocket/cush

i noticed a miniscule amount of back and forth movement before piston moved.
this is with everything cold
but its enough movement to make an audible nocking

is it normal to have a tiny bit of play when cold like that?
the big end in all previous checks has presented itself as being good

the time i had play on the shaft, it turned out there was a bearing missing.
normally the cush drive should take up any end float. check and make sure you got all the right spacers and check the bush and nut ect on the timing side.
hope fully some on hear will give you some more info.
barry

email (option): mrsbfuller@hotmail.co.uk

Hi There
Check that your not confusing "movement" with the piston rocking from side to side in the bore. This will produce a knock (slap) which providing your piston clearances are within spec is normal. To check the big end there should be no vertical movement when the conrod is grasped and an attempt made to lift it up and down at TDC. In this case don't confuse this with play in the main bearings or side to side play in the conrod, the former is bad the latter normal.
Regards
P.S. Also check the small end.

I think Kieths assessment is correct...What you can feel(and hear) is more than likely the piston clearance when cold and isn't anything to worry about.
There will be some end float of the crank assembly within the cases until the engine shock absorber assembly is fitted and tightened up...that is normal. There should be no up and down play of the shafts/bearings within the cases (which very rarely occurs anyway).
The test you describe is not a valid one, or correct one, for play in the big end or small end. That must be carried out with the barrel and head removed. There should be no perceptible vertical movement in the big end bearing when tested but there should be approx. .010" end float of the conrod between the flywheels...Ian

email (option): ian@wright52.plus.com

I suspect that what you're talking about is a perception of backlash in the crank and rods. You're converting the rotary movement of the crank into an imprecisely measured vertical movement of the piston and the crank is always going to turn slightly before you can detect movement at the piston. It's the reason that a degree disc on the crank is more accurate than a rod inserted in the cylinder.

If the engine was running OK before then I'd suspect that you'd hear a knackered big end before you'd feel it.

thanks you lot

yea i am a panicker

I kind of assumed all of those things, but thought i'd ask

just for info
small end is new
piston and bore are new
crank is shimmed to centralise conrod
no up and down movement was detected on conrod when barrel was off
cush is fitted.

yea thanks for the info.

SAE 50 oil will take up a lot of slack

email (option): deadsheds@yahoo.com

There is always a good few degrees of crankshaft rotation before the piston appears to move, possibly even as much as 20 degrees, before you notice the piston moving, to find TDC you would split the difference on crankshaft movement and when you use a degree disc you'd be surprised how many degrees you'd see before you notice it moving, so this isn't really an accurate method of assessing crankpin/ big end wear.

email (option): davmax@ntlworld.com

In the 1st 20° an M20 piston moves down .136" from its TDC position.

email (option): sales@victorylibrary.com

Yes, but you've got a few degrees of crank movement as the piston comes up to TDC to do the test, and there could also be a bit of wear on the small end bush or piston to gudgeon pin , all I'm saying is that it's pretty well impossible to detect perceptable wear on the big end if any of these other factors come into play, the only real way to check is to remove the barrel and wash the big end out with petrol to eliminate the oil masking the wear and smoothing out any roughnes. I wonder what an extra 0.001" on a small end does to the measurements when measured in degrees?

email (option): davmax@ntlworld.com

Checking a big end bearing by 'feel' gives an indication of its likely condition but the absence of any play should not be considered a guarantee the bearing is good...
Recently I stripped one that had no play at all and felt good but the crankpins bearing surface on one side had completely gone over a length of about 3/4"...The lack of play was entirely down to the bearing being 'supported' by the unworn half of the assembly...
The only way to absolutely prove a bearing is good is to strip it down, and running one that has not been stripped should always be regarded as a 'calculated risk'...(unless you have X ray vision)...Ian

email (option): ian@wright52.plus.com

I always strip any that come to me regardless of the feel of them, I just use the feel to give me an idea if it's going to need new bearings or a complete pin

email (option): davmax@ntlworld.com