To mill or not to mill

[wnarace]

I am in the process of rebuilding a 416ex, which has a wiseco 11:1 piston in it. I have been reading that the actual compression for this kit is lower than advertised, so I took some measurements. I came up with the piston sitting approximately .033 below the top of the cylinder with no base gasket. If I add a base gasket that puts the cylinder .053 below.

Then you add in the head gasket and you are well below the optimum .040 squish.

What do you guys recommend should I get the jug milled, use no base gasket w/ a thin head gasket, or use the cometic gasket set that wiseco supplies. Wiseco's tech claims that with their gasket set the compression ratio is dead on.

Thanks for your help in advance!!!

[Brahmus]

On this topic.. What compression psi would indicate a correct 11:1 ratio? What is stock on a 400EX? Is there a formula?

[wnarace]

Originally posted by Brahmus
One this topic.. What compression psi would indicate a correct 11:1 ratio? What is stock on a 400EX? Is there a formula?

I never did a compression test on this bike it had a head gasket blown when I came into the picture. Sorry for no additional information.

[GPracer2500]

It's a good topic and I like your attention to detail.

What would the squish be with no base gasket? How thick is the head gasket? If the numbers came out favorably it might be a way to avoid machining. You may not want to run without a base gasket though--I don't know. Worse comes to worse you could always add the base gasket later.