Piston Bump clearance measurement - HELP

[zambant]

I hope some of you silver hair experts out there can help please

I have an elderly MD2B and have just overhauled the top end.

The cylinders were not disturbed where they join onto the crank case.

The heads are back on with gaskets and torqued up.

I am proposing to measure the piston - cylinderhead clearance by poking a soft piece of lead wire through the injector holes and measuring the resulting squashed wire with a micrometer.

Is this OK or does anyone see any problems please??

Thanks

John

 

[rob2]

I've never done it myself, but I believe it was normal practice, particularly if the sleeves had been refitted. I guess if the gap is too small and it breaks off the wire you've got to remove the CH anyway, so nothing lost.

Rob.

 

[Como]

According to my MD2 service manual you should use a lead wire apprx 2mm dia inserted through the injector hole, turn the engine through TDC and then measure the flattened portion. The measurement should be 0.8 to 0.9 mm (.031" to .035").

Hope this helps.

John

 

[Bilgediver]

According to my MD2 service manual you should use a lead wire apprx 2mm dia inserted through the injector hole, turn the engine through TDC and then measure the flattened portion. The measurement should be 0.8 to 0.9 mm (.031" to .035").

Hope this helps.

John

It might not be flattened the first time if you did not push enough wire in for it to bend around and reach the bore and just lay in the piston depression.

 

[VicS]

If the engine has been dismantled there is a procedure in the workshop manual for measuring the depth of the piston crowns below the top faces of the blocks to determine the correct shim thickness between the blocks and the crank case.

However if the engine has not been dismantled the compression can be checked with a lead wire. The procedure is also detailed in the workshop manual and is:

The workshop manual can be found at http://bluemoment.com/downloads.html

 

[sigmasailor]

I was used using lead wire to measure clearances in bearings. We replaced this (I'm talking 35 year ago) by calibrated plastic wire called 'plastigauge' (it's still around: http://www.plastigauge.co.uk/). The advantage of this that's is softer so you cannot damage any parts and you do not need a micrometer to assess the clearance. Clearances in bearings (the nice old ones which you could scrape to fit) were around 0,05-0,10 mm if I remember well. They have the stuff for all clearance ranges.

On the other hand if you didn't change anything and used a correct gasket I wouldn't be worried about compression room too much. Just start it up and see how it starts and runs.

Eric