Inliners International Forums General Discussion Engines Core shift question...

I found what I thought might be a nice 250 to build, '72 with only 39K miles, never rebuilt, but the core shift seems bad. I read where ideal is a 3/8" machined strip on the #1 cyl. This one starts about 3/4" wide at the top to a point not really even all the way down the cyl wall. No picture due to the photobucket thing, sorry.

So how bad is too bad?

If you are really concerned - take to a shop that has a ultrasonic thickness gage and get then to check the bore wall thickness. Then you will know. The other method uses a SMALL ball peen hammer - lightly tap the cylinder walls 90* apart over the length of the bore - if the wall is thin - it will make a tinny sound.

You are never going to find any engine block that is ideal because of core shift, only what you are willing to live with for your intended purpose. The major thrust side cylinder wall thickness is the most important thing to look at, not the front to rear core shift which has very little thrust force applied to it compared to the side to side loads as the crankshaft rotates. And this side to side core shift of the cylinder walls is the most critical and important. Only a sonic checker will detect and confirm these thicknesses and core shift for you. The Mexican block castings are typically thicker than the USA or Canadian blocks, but I have also sonic checked a few of them that were no thicker. So never rely on what you've read as fact and only rely on actual measured data from yourself or your machine shop.

Good advice, thanks guys. I'll get that cyl wall miked before making a decision which way to go. The 250 in my '68 pick-up is getting pretty long in the tooth and I'd like to have a replacement ready, or at least ready to be ready. I'm not planning on building for crazy HP, just a nice, strong driver.