Changing chain housing in situ

[motomiata]

Being a 911 engine virgin I am bit intimidated by the task I am facing. Advice an encouragement is needed

Starting upgrading the chain tensioners on my '72 2.4T I realised that the left hand axle stud on which the idler rides was completely loose. It actually came off along with the idler. The chain housing must come off and be repaired or a good used one installed.

It's my intention to do this without dropping the engine, which seams feasible after removing the rear bumper, the muffler and the backplate.

I have read everything directly relevant on this forum and I have got (and read) Waynes engine rebuilding book plus Andersons Performance book.

I anticipate the job can be broken down to the following steps:

- Crank at Z1, cylinder 1 at TDC with both valves "loose", dizzy pointing at 1
- Remove chain tensioner and idler
- Remove 46mm nut taking care not to rotate camshaft or crank (got the right tools)
- Remove the dowel pin and the camshaft sprockets + the chain. The camshaft will turn slightly due to the spring loaded valves+rockers
- Remove the inner sprocket / adjustment flange
- Remove the camshaft housing end plate
- Remove the chain housing, fix it or replace it
- Reverse above making sure the chain has not slipped off the intermediate shaft sprockets (checking through drain sump)
- New seals all over of coarse
- With the chain and tensioner back on, the cam is turned back to original postion with the mark facing up. Dowel pin inserted
- 46 mm nut torqued to final value (is this really nessecary at this point?)
- Valves on 1 adjusted to .1 mm
- Crank turned 360 degrees, camshaft 180 degrees
- 46 mm nut off, dowel pin out (keeping camshaft from turning)
- turning camshaft to valve overlap lift of 2.6 mm
- dowel pin in, 46 mm torqued to final value
- double check cam timing

Have I got it right? Any pitfalls?

Any advice, comments and recommendations will be highly appreciated, thanks

Hans

[MBruns]

I have a feeling you are going to have to strip the rockers and shafts on that side as well to move the cam toward the front of chassis as with the nut drive cams you can't get the chain housing past the snout of the cam in normal position, the bolt style you can do it as it is shorter. If its still MFI you can change the seal as well, if not bump out the freeze plug and replace.

Mike Bruns JBRacing.com

[Walt Fricke]

Hans

Mike has built a lot more motors than I have, but if I had to guess he has mostly done this after a full (or at least top end) full teardown.

I am pretty sure that I once was able to get the chainbox (weak memory says the left side one) off without having to pull the cam. This was on the early style cam with the big nut and protruding snout. My recollection was one of some wrestling in each direction. While I can't remember why I would have had to do this, it might have been because I made the mistake of installing the cam and a bunch of rockers before I put the box on. A bit easier to install rockers that way, though I now know that was a bad idea overall for several reaso

In any event, you should try it - you have nothing to lose. If you can't wiggle and fiddle the box off over the cam, then you can go to plan B.

To start, I'd plan on supporting the rear of the motor on blocks, and I'd remove the motor support - at least the cross piece. That will give you a bit more wrestling room. I assume you already have the muffler off.

For Plan B, I'd be inclined to pull the motor out of the car. That way you can just remove the camshaft in the normal way. I'm pretty sure you won't have room to do that with the engine in the car, but it would be worth a close look to see if you could to it, perhaps using the partial drop technique to change the angle of everything. Remove the rear (below the bumper) valance, too.

Mike's suggestion to use the cam to knock out the plug so you can move the cam the little way forward that you might need is ingenious. But do you have the needed working room with the engine in the car? I guess you can get in there to remove the vertical sheet metal plate? Awful lot of CIS parts in the way there. And will you have enough access to tap the plug back into place?

Good luck. Much more work than you had bargained for. I remember the tensioner update as my first experience working on a 911 engine. I'm sure glad I didn't run into something like this!

[motomiata]

Mike & Walt,

Thank you for your comments and advice. According to Waynes engine rebuilding book, the chain house should come off without removing the cam (page 31-32), provided the steel sleeves between the case and the chain house stays in the case.

I will certainly give it a try. The car is a 2.4MFI and as the problem is on the left hand side it's not an option to remove the cam without dropping the engine.

Torquing the 46 mm nut seems to be the most tricky part. Reading the instructions in Waynes book and elsewhere, I dont understand why it is nessecary to torque the nut with the crank at Z1(cylinder 1 at TDC), turn the crank 360 degree, then undo the nut and do the cam timing. Any logical reason for this manouvre ?

[kwikt 911]

It can be done. I've done it a few times on my 72 911T. It DOES take some wiggling around but it did come off. If the mounting studs in the case were just a little shorter. Or the cam end was ground off a little would definately make it easier.

[Walt Fricke]

Hans

Perhaps you misread Wayne's book. I'd dig it out to see, but the fact is that you don't need to put final torque on the big 46mm nut at any point in the process until you are sure you have the setting/reading you want (or will accept, within a tolerance). Up to that point you don't need full torque.

If you start at Z1 firing (both valves closed) and just put the pin in the cam (which is oriented for that) so that you can set your gauge and rotate the cam to start measuring overlap, you can finger tighten the big nut - the pin will do the work of holding things for your next move.

When you get back to Z1 with the cam 180 degrees from where it was, take the nut off, pull the pin, and put your cam tool on the end of the cam. With the tool, rotate the cam until you have the reading you want on the dial indicator. Reinsert the pin. Put the nut back on finger tight. Then put the holder on it and tighten it. How tight? Well, snug - I do this without a torque wrench. To where it is pretty tight, but not so tight it will be a pain to undo if needed.

Spin the crank twice to see if you come back to the reading you had, or close enough. If not, loosen the nut and see if you can, without moving the pin, get the needed reading. You can get quite a bit of needle movement from one end of the pin slop to the other, and you should be able to get what you want, because you did to start with and it just slipped a bit when you tightened things. Resnug the nut and keep going.

If all was well on the first try (sometimes it is), or after however many tries, now it is the time to apply the specified full torque. I use a pipe over the handle of the holder which is long enough to reach the floor to hold the cam. That way I can use both hands on the torque wrench which has the crow's foot on it and get the needed torque.

I used a cheater bar pipe once which was too short, so it only came part way up the holder handle when its bottom end was at an angle and on the concrete floor. As a result, I bent the handle some! So my pipe slips all the way up to the holder socket and extends out at about a 45 degree angle to the floor where I have my engine stand.

If you are confident you understand things, and can keep track of them, you could do things a bit differently: first, set the rocker clearance on #1 when doing the left side, and spin the crank 180 degrees so you are at overlap. Then set up your dial indicator so it will be ready when you need it again. Then pull things apart, fix the chain box problem and reinstall whatever you are going to use (trying to move crank and cam as little as you can, but don't fret a bit of movement), reinstall the chain and gears without the pin or washer or nut, and then tension the chain in the normal way for setting timing.

When that is done, check the crank and reset to the Z1 it was at (it should be pretty close if it moved at all). Then rotate the cam the (small) amount to get the reading you need on the indicator. And proceed as normally from there.

If you get lost, you have the distributor to give you a general idea of where you are. On a normal full rebuild the distributor often has yet to be reinstalled, and generally you wouldn't trust it as a result. But here it will tell you which cylinder is firing, which in turn will tell you whether you are on Z1 firing or Z1 overlap for both #1 and #4 cylinders.

p.s. - an awful thought: Since the stud on your left chain box failed, what about the similar one on the right housing?

[motomiata]

Walt,

Thank you for your detailed reply and description of "how to".

As for mis-reading Waynes book, it's clearly stated on page 167 (and this is specific for the high-lift, high-duration type) that the 46 mm nut must be torqued fully before rotating the crank from Z1 to the cam timing position.

The CIS/Motronic type does not need the nut torqued, as described on the preveous page.

It doesn't make sense to me, wheras your description does. What count must be the final overlap timing value when the nut is torqued. Hopefully Wayne or someone else with a deeper insight will chime in and comment on this.

The right side is thankfully OK. Strangely, the loose stud looks perfect with a snug fit in to the chain house. Seems I just prevented an engine disaster.

[Walt Fricke]

Hmm. The higher the lift, the more the cam will want to get away from you at overlap. But it still isn't that much torque. While ultimately it is the clamping force of the torque, and not the pin, which keeps chain and cam together in the same orientation, that little pin is plenty strong. I had a cam sieze. The pin broke all the "teeth" off of the inner piece, and showed no signs of shearing itself.

My race cam overlap is 5.6mm, no problems setting it beyond the usual.

Ask Wayne directly about page 167. I like his books, I've read them, but I was assembling my own motors before Wayne's books came out, based on Haynes, Bruce Anderson, and the factory manuals, so naturally I revert more to what I'd been doing (where it worked) than his excellent descriptions, so something like this wouldn't stick. I will say that he has cam carrier and head stud bolt tightening patterns in his engine book, and you won't find those anywhere else. A surprise to me, since all VW manuals have that. Great book.

Walt