Measuring mag case warpage
 

I took apart a mag case 2.7 and did a measurement of the half case.
All green numbers indicate height difference as seen from above, the blue are measured as offsett from one carrier to the next (crank direction)

So I can see that the middle part is bending out by max 0.05mm, but the case is so soft I can easily add 0.01-0.02 mm buy pushing with one finger.

So the question is, does this case need to be decked and aligne bored?

just to clamp it down to a surface grinding machine will be difficult so not to introduce any flexing to the case that will come back once released.

http://forums.pelicanparts.com/uploa...1515448518.jpg
http://forums.pelicanparts.com/uploa...1515448518.JPG

I like to check the mag cases for straightness by taking a std crank with a new set of std bearings and installing both in the case with assembly lube. Torque the saddle bolts and perimeter nuts and check to see if the crank rotates smoothly with minimal effort.

You cannot accurately measure a used case like that. The only valid measurements you can make is with the case halves bolted together. There is a certain degree of "set" on a used case.

Exactly.

And if it rotates its OK???

All you are measuring falsely is the clearance to the bearing, and to some degree the alignment, but you are not measuring the bearing shell clamp.

This, is way more important than measuring the clearance when the case is cold. You have to measure both the alignment and the housing bore size so the shells are clamped properly. This will allow them to become as round as possible so they measure as designed.



There is a right way to do this and this is not the right way.

In my original reply, I left it unsaid that the individual case bores need to be verified as standard size and round.

I would add that when checking with a crank installed that one use regular oil and not assembly lube which is quite thick and can naturally make the crank a bit more difficult to turn. If measuring minus the crank, the nose bearing must be in place to get any sort of accuracy after all the through bolts are torqued. If clearances are too great in some areas then work would be necessary. The saddles tend to go slightly oval in the thrust direction from the rods, so straight down if you're looking at the case half flat from above. The caveat to all this with mag cases is the material lends itself to move around a bit anyway.

The primary issue as I understand it with them is that they be kept within reasonable operating temperature as higher then that on a regular basis then stuff starts to happen a la 75-76 US spec emission engines.

So for me, and take it what it's worth which isn't all that much as I've only done 2 of these but I've done loads of Ferrari motors, if the crank is moving freely and the clearances are ok ish, invest the capital in a 44 or even 50 row Setrab oil cooler depending on the build and expected bhp to make sure it stays within temp.

As a manufacturer of cases, and as one who has spent more time measuring old cases both by hand and with scanners, computers, and CMM machines than probably anyone alive right now, I can tell you with the utmost certainty that the OP's method of measuring a used case is nigh on useless to provide any meaningful data because the cases warp.

Tom's method, while abbreviated and not fully fleshed out, is a more correct way of determining whether the case is good or not. No one (including Tom) stated that his method was 100% complete.

Remember, the case's MAIN FUNCTION is to hold the crank. If the case is bolted up and a standard crank with new bearings turns freely and exhibits proper clearances on each journal, there is a great chance the case is OK, and that is what Tom was saying.

There are other methods, but his is a quick empirical method used by many.

After measuring the bore/bearing/journal sizes/clearances, to ensure they meet spec....installing the crank/bearings and verifying that the crank turns freely....is a good thing. You just need to invest a little in the measuring tools, to allow you to do this properly.

regards,
al