A Question For Engine Builders / Machinists / Engineers!

[Jimbob-Squarepants ©]

When a short block is overbored it is measured in Thousands of an Inch (e.g. +0.90 is Ninety Thousands of an Inch). For this to be done, you will need to know the original bore size of the block needing the work and then over bore it to the required measurement. Am I correct?

 

My question is this: What tollerances do you allow between the piston and the cylinder wall? Is there a standard measurement or is each engine different?

 

On that note, can someone tell me the exact bore measurement on a standard 1300 Crossflow cylinder?

 

Thanks very muchly

[radar tech]

according to the haynes manual. the 1300 standard block bore is between 80,947mm to 80,957mm ( 3,1869 to 3.1873 in.)

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[lee 1]

Not sure on the standard crossflow bore size,but the piston to bore clearance is dependant on the pistons and should be specified by the piston manufacturer

[Toby]

I believe most people measure the piston (at the widest point on the skirt) as pistons aren't round when cold, and then bore to suit. Clearances vary from about 0.05mm (0.002") to about 0.15mm (0.006) depending on the piston material and intended use, ie a turbo would possibly be bored a bit looser cos of the heat the pistons will see. As suggested the piston manufacturer would normally spec the clearance, and the experienced engine builder may choose to deviate a little - usually upwards.

 

If you are enquiring for your set up take the pistons along with you to the reconditioners and I'm sure they'll know.