Mag Case 2.7RS+ Build

[Rosco_NZ]

So I have:
- 7R Case prepped by Ollies (align bored back to std)
- Crank ground to meet new 0.25 under main bearings
- Rods machined to size
- Used 4 rib pump
- New IMS bearings.

I tested both the crank and IMS individually into the cases to check they spin OK. Seemed fine though the crank was a little tight I put this down to thick assembly lube. I checked IMS gear backlash (new alloy gear on old crank) .. there was some very minor play between the gears, tho’ I did not measure it.

When assembled and torqued, the crank seems tight .. it will turn by hand by pushing on a rod but takes a bit to get it moving ..

Maybe this is normal when everything fresh machined, new bearings, crank trying to drive IMS.

My suspicion lies in the IMS gear backlash … as only thing I haven’t measured. Case is ‘0’, IMS gear ‘0’, looks like crank gear has ‘0’ hand etched onto it.

But there’s nothing that can be done anyhow to give a bit more backlash if in fact it’s a bit tight.

So what to do ..?? Don’t over-torqued and assemble anyway ..?? I’d hate to muck things up now …

[drgouk]

Did you check case tunnel for Size, Taper and ovality, If so how much?
Ims tunnel Size, Taper ,ovality?
Main Bearing clearance?
IMS bearing clearance?

Can you feel any backlash when you try and rock IMS shaft back and forth?

IMS endfloat?

[Mark Henry]

IMS thrust bearing, the thrust often needs to be sanded (flat glass and sandpaper) a bit for end play clearance. I forget the exact spec but you need something like.002-.003" clearance.

New #8 bearing? Check the spec, when I built my engine the new bearing (bearings, I tried more than one) was so bad (on the ID) I ended up DFL coating and using the old factory bearing.

Try just oil with some blue STP mixed in, I've used this for assembly lube in the VW Type 1 and 4 motors for years, only thing STP is good for IMO. For 911 I use 'Clevite Bearing Guard', it's a sticky but not thick assembly lube.

The main bearing thrust needs to be checked, it can be checked with a feeler gauge if the engine is apart, IIRC you want .003-.006".

I'd talk to Ollie's about the cam gear, an old chap here (long gone) who used to do VW line bores back to std like they do on the 911 cases and he would trim the cam gear to match. Not sure what exactly he did, but he forgot one time when I was PU a case and it only took him about 10 minutes to do this job on the gear.

[targa72e]

Sounds like you have had the appropriate work done. As others have said measure all the appropriate clearances and make sure they are in spec. Some have had work done and found things out of spec when measured.
If you search this forum there are some post with the a torque spec that should be required to rotate engine with just crank installed. The statement takes a bit to get it moving" is not a very measurable result to offer advice on.

John

[Mark Henry]

How much are you tightening the case?
You need pretty well full torque to get the correct bearing crush.

[mikedsilva]

Originally Posted by Mark Henry

IMS thrust bearing, the thrust often needs to be sanded (flat glass and sandpaper) a bit for end play clearance. I forget the exact spec but you need something like.002-.003" clearance.

Yes, lately I have been assembling the case with just my IMS shaft and found that the thrust bearing does indeed need a little fettling for it to be able to turn freely.

[Richey]

I've had problems with new IMS thrust bearing end play also , too tight

[dannobee]

With the crank, IMS, and crank seals installed, the rotational torque is usually less than 25 in lbs. That's with the chains dangling, both crank seals installed, rods installed but not pistons. FWIW. I don't recall ever seeing a factory spec, just going from experience here. And you'll need a beam style torque wrench to measure it, as the value goes up a tad before the crank starts turning (let's call it "breakaway torque.") If you don't have a torque wrench that measures that small, you should certainly be able to turn it over with one hand on the crank pulley.

[Rosco_NZ]

An update … the crank was assembled with assembly lube … very sticky thick stuff. How much resistance does is put up ….. lots and lots … to the point you think the crank is tight. After disassembly and reassembly without any, the crank spins like a top! Well almost.
And as far as IMS backlash, was only able to measure 0.02mm .. but the gears are not loaded at all when static. So I think we’ll call that OK.
Regarding the IMS bearings, massaging the shell ends on a piece of glass on 600 grit took off a few high spots and gained us a smidge of endfloat. So we’ll call that a result too. Progress!!!
Onwards!!!!

[Jonny042]

I know you're past this, but I always test assemble a bare crank in the mains without seals, running on oil. I caught a burr on a main bearing shell once that stopped the crank dead but would have been masked if I wasn't checking it in this way.

This is analogous to the connecting rod gravity drop test.