How do I measure compression height correctly?

[McBreadhead]

Have to buy new forged Accralites for my 1760cc xflow but need to check I have correct compression height.

 

Do I measure from centre of gudgeon pin (difficult) to piston crown or from bottom of gudgeon pin (easier) to crown? The value I'm looking to achieve is circa 44.75mm as per mfr data.

 

If it's from the bottom of the pin I'll need to knock it out a bit to allow the vernier to sit square - I assume this can be done with a gentle tap from t'other side once circlips are removed?

 

Ta in advance

[Rob Walker]

Your lossing me I usually measure the compression ratio by filling both the head combustion chamber ( not required on a flat XF head) and the top of the piston in its bore at TDC using parafin and a pipet and a flat piece of perspex. You must also make an allowance for the head gasket by measuring the thickness of an old one and calculating its volume.

 

Could you not send Accralite one of your old pistons and ask them for the same spec?

 

Edited by - Rob Walker on 11 Sep 2007 19:22:36

[Ian Macquarie]

The diagram in the Burton's catalog shows gudgeon pin centre to piston top.

If you are only trying to identify whether you have the long rod or standard rod version (ie 44.75 vs 37.2 mm) I'd have thought it would be fairly easy even with a ruler. Mind you, I've never tried it!

 

Ian

 

[McBreadhead]

Ian,

Thanks I have measured 34.83mm as directed so have obviously got some weird mix of components here.

Nick