Thread: HELP !!! Rebored or not ??

The only sure way is to measure the bore and crankshaft journals.

John

How do I measure the crankshaft journals

Originally Posted by Themadmob

How do I measure the crankshaft journals

With a micrometer, some engine builders will stamp the crank if its been ground undersize with the size, ie 020/030 etc.

Thanks but how loanrangie ?

Originally Posted by Themadmob

Thanks but how loanrangie ?

If you need to ask that then maybe some one else should be doing it, you can measure the big ends by removing a conrod but mains will need to be measured with the crank out.

Something like this will get you a std/rebore/regrind dimension although not accurate enough for fine measurements:

150mm 6" Electronic Digital Vernier Caliper LCD Gauge Stainless Steel With Case | eBay



Cheap too.

Thanks Loanrangie .. I know my way around engines but have never had to measure if the engine has been debored etc ... Thanks for your help

theres a hadful of measurements you need to have in advance and need to make to determine what you're looking to have answered.

I considder knowing how to do the measurements to be the barrier test to if you should do this yourself or have someone else do it for you.

its not normal for the mains on the block to be machined out unless the boreline is off you need to have the measurements for the cylinder bore diameters and the crank main and big end journals.

if your bore diameter is larger by more than the nearest 10thou inch at its smallest diameter its been rebored oversize. if your crank journals are undersize by 10thou inch at their largesst diameter then its been ground undersize.

your bearing shells, pistons, crank and block should have markings on them to inicate thier existing state unless theyve been done by back yard cashies.

dont forget that when you are looking for your next grind state you have to go on the maximum diameters on the bores and the mins on the crank, you judge the existing state by the mins in the bore and the max on the crank.

Dont use verniers. if you dont know what the appropriate tools are to make the measurements then you should palm that off to your engine builder or have someone who does know do it for you. this is one of those "art" things you can read how to do it in a book or online but doing it live has a bucket load of feel and experience to go with it. muffing a measurement by just a single thou is enough in some circumstances to make a job go from built to tolerance to "pooched and doomed to early failure"

you can use the verniers for a very broad go/no go in the early stages but theres an art to that too because the way that gets done you're not likely to find in any book.