MFI Cam Pulley Problem

[Tanick]

The bolts holding the lower pulley to the left cam shaft have sheared on my engine. At the time I was driving through France and noticed a regular drop in power about every 3 seconds or so. I stopped to find the belt a bit loose bit put the problem down to ignition. The car got worse and worse and eventually stopped. I checked for a spark which was there but found after a lot of cranking the plugs were dry. After checking that fuel was getting to the MFI pump I checked the belt. I could turn the belt from the top pulley - the bottom pulley was just sliding. I got the cover off the back of the engine (not easy) and found the 2 screws holding the pulley to the cam were broken. I couldn't fo any more by the roadside so called the breakdown service.

3 weeks later on, the car has just been delivered back to me in the UK. Over the last few weeks I've been planning my attack and have bought a couple of splied thread extractors and a set of Left Handed Cobalt drill bits from Snap-on. My plan is to remove the LH heat exchanger and try to drill out the broken screws. They are broken 1-2mm below the surface of the cam.

I'm hoping not to have to drop the engine and I'm really keen to avoid removing the camshaft

I can't find any history of anyone else having this problem so I'm posting to see if anyone has any other suggestions or warnings about what I'm about to attempt.

Thanks
Nick

[jstobo]

I don't see how you are not going to have to drop the engine. I can't imagine there is enogh room to get a drill and bit behind the cam with the engine in the car. You shouldn't need to pull the cams though. You have the right tools. Take your time and all will be well. Use a center punch to indent the broken scews so your drill bit will be centered and you won't hurt the threads in the cam. Good Luck.

[svandamme]

try not to break the left handed Cobalt drills
if you do , you'll be in a whole lotta trouble

ask me how i know



this is what happens if the PO torques 944 Camhousing Bolts by method of Guestimation, can you see the broken bit in there?? total PITA to drill out the remains...rockhard, took us the better part of an afternoon to get out that one bolt + the bit inside...
camhousing was a write of , but that was obvious the moment that bolt got stuck... no way to get any tools near the bolt...

[Tanick]

Actually there's about 18" of space once the heat exchangers are gone. I may remove the shock absorber too. I just wish I was left handed.

SVandamme, I don't want to know what has gone on in your picture

[Grady Clay]

Nick,

I suspect you may be able to get the remaining screws out with just a pick. Try that first.

If all else fails there are two other holes in the end of the cam. They are not taped as they were used for roll pins to drive the Sportomatic oil pump. I believe they are on the same circle as the Gilmer belt pulley bolts. You can tap them and attach a MFI drive pulley. These holes are 5 mm and will need to be drilled for the M6 tap size.

The MFI drive set of three pieces (drive pulley at the cam, belt and driven pulley at the MFI pump) should be replaced as a set. One worn part will cause the others to fail. Use your ”good used” parts as roadside spares (with some bolts, HeHe.)

BTW, your missing screws are M6 x 12 mm socket head cap screws, grade 8.8. The screws are Porsche part number 900.067.008.02 and use a spring washer 900.028.003.02

I suspect the pulley may have been loose for quite some time. I bet the pulley is now damaged. Your poor running was probably the pump timing constantly changing as the belt skipped teeth on the wobbly pulley. Carefully inspect the end of the cam.

You may want to use this opportunity to replace the oil seal at the cam. Be very careful to not damage the sealing surface on the cam or the bore in the cam housing. If you install the new seal with sealant, make sure there isn’t so much as to restrict the drain hole. That hole needs to pass oil back into the cam housing or the oil from the bearing will pressurize the seal and it will leak.

Best,
Grady

[Tanick]

The MFI drive set of three pieces (drive pulley at the cam, belt and driven pulley at the MFI pump) should be replaced as a set. One worn part will cause the others to fail

Thanks Grady, you're on the money as usual. I replaced the top pulley and the belt about 1,000 miles ago when the car was being restored. Didn't check the bottom pulley other than visually. I may have to resort to tapping out the 2 roll pin holes as you suggest. Those screws refuse to come out.

[Grady Clay]

Nick,

I don’t think you will need to drop the engine. Removing the heat exchanger, LR shock, axle, heat control, parking brake cable, etc should give adequate clearance if needed and all are easy.

Is the remaining bolt free in the threads in the cam? Is it that it won’t unscrew? If so, you might take a “bottoming” 4-flute tap and grind it slightly shorter. You can use that to chase the threads above the bolt remnant. That might allow the piece to thread out.

Another approach could be to glue (Super Glue?) a small tube on the remnant and use that to thread it out.

Of course there are the Easy-Out and reverse thread procedures you noted.

There is even enough material there to completely drill out the bolt remnant and threads so you can install a HeliCoil or other threaded insert. There is nothing to prevent using a fine thread M7 bolt. You would need to enlarge the clearance holes (slots) in the pulley.

The cam is cast steel so you will need cutting fluid for drilling and taping suitable for that material. Leave the oil seal in place until you are finished with the bolt removal task.


Enquiring minds here in the States would like to know your saga of getting your 911 back home to Herts. Many might bring their 911 on tour in Europe and UK if there was an easy way to deal with situations like yours.

If you tour North America with your 911E, you will find Pelican and PCA help everywhere. Not to mention the normal commercial AAA and other. Consider that for your next “driving vacation.” I’ll host a Colorado Tour for you.

Best,
Grady

[Tanick]

Grady, I love Colorado. After finishing University I travelled the states (getting to know the girl who is now my wife). I spent a week in Denver and 2 weeks in Glenwood Springs (most of it down the sulphurous holes). decided that if I ever became rich I'd move there and indulge my passions - winter sports and driving.

I removed the heat exchanger and shock tonight and drilled the screw out to take the extractor. My cam shaft didn't like it and gave up the fight. I now have this:



I drilled it out using a variety of drills but ended up with a HSS 3.5mm bit, the cobalt pilot drill was good, but the larger sizes were too brittle and fouled and chipped on the previously drilled hole. I guess the extractor expanded the broken screw and crumbled my cam that appears to be made from cast cheese not steel.

A good Rioja is numbing the pain while I summon the courage to tap out the roll pin holes.

On the subject of touring in Europe, my classic car insurance policy includes European Breakdown cover using Europ Assistance. I broke down at Classic Le Mans in July and called them out. The guy Joseph (who was making his year's income there that week and virtually living at Maison Blanche) couldn't fix it. This happened on the Friday afternoon and I told him I wasn't leaving till Monday. I was camped up with the DDK crowd so had probably 90% of the UK's early 911 experts within 100 yds. Joe told me to call him on Sunday if I hand't fixed it and he'd take my car to the ferry. As it happened, the problem was fixed by a very nice chap called Gary and I didn;t need Joe.

There are many options, if you were to ship the car to the UK and start there, you can get AA (www.theaa.com) and RAC (www.rac.co.uk) both offer english speaking breakdown services across Europe. Sure, you'll pay for having an old car. I've just looked for a quote and got GBP 209 for a year's cover but there seems to be an issue about being a UK resident.

On this trip, I was heading down to Champagne for the weekend and the car gave up. It was towed away to a local garage. I don't speak French very well and it turned out we were left waiting for the breakdown people to authorise the bill for a taxt to my hotel. As soon as I found out I said I'd pay the 50 euros and they booked a cab. I could have had a hire car but my wife was already at the hotel in her car so I didn't bother. My car turned up at my house in the UK 11 working days later. They aim for 10 days. UK and northern France has had a very wet August so I have some damp carpets and I had to pay 100Euros parking charge but in all its a good service.

[Grady Clay]

Argh

I guess that answers the question about removing the engine and cam. I am very sorry to see that. I only wish we could have done “remote surgery” from the States and prevented this.

That image seems to show that the cam is broken where the seal rides. If so, I don’t see any easy repair. A new camshaft is probably the only solution – DAMN.

The issue here now becomes matching rocker arms and camshaft. This is quite a bit more than simply unscrewing a couple of broken bolts – DAMN again.

If this is the case, you are faced with the decision to just repair the damaged cam and associated rockers or do more. Do you repair the 4-5-6 side also? Where do you quit? Tough decisions resulting from something so simple as two loose bolts.



Perhaps after this technical issue is resolved, you can have a “second honeymoon” here in Colorado. I’m offering to be a contact and help with arrangements if you want. There are lots of Porsche friends here and you guys are very welcome. The cost can be very low with our planning.


Perhaps there can be a similar group in the UK and Europe. You can help make that happen.

Best,
Grady

[Tanick]

The broken part isn't that deep, the broken part is well clear of the cam oil seal. I think that threading the roll pin holes is the only option now. I'm worried that the cams won't take it as they are so weak. Are 911 2.4 e cams available?
'

Check out the DDK website - www.ddk-online.com, there are loads of us here in the UK (and english speakers in Europe) who benefit from the Pelican boards and who would be glad to offer support here, whether it be technical help or just help in arranging travel. I'd be more than happy to store a car in my garage in the event of any problems.

[Tanick]

Here's another pic of what I'm dealing with



going back to travel in Europe, I'm sure that there are many of us on DDK that will help arrange travel. Post on the site and see what happens, I understand that you wouldn't want to post on a UK site if you travel in france, but you'd be surprised at the diversity of members.

You are welcome at my humble abode in the Chiltern Hills anytime.

I'm very interested as to what remote surgery would have done. It was all going very smoothly until thre camshaft gave up.

[Tanick]

Tapped out the holes Took a few hours but it worked. I didn't need to drill them any larger, they were perfect . I've ordered a new pulley today from our hosts and when it arrives I'll have to open up the holes a little to make it fit as they don't align exactly, the new holes are a little less than a millimeter closer to the edge and not exactly at 180degrees to each other. I can't think of an alternative. Is there a particular reason that they use screws? I've got a load of M6x20 bolts left from the engine tin.

Thanks Grady for all your help.

[andyjboy]

Great news Nick.

I don't think that there's sufficient room to get hex-headed bolts inside the pulley...

Well, if there is, I don't think there'd be enough clearance to get a socket on them.

[Tanick]

Hi Andy. I didn't think of that about the screws. I'll have to find some allen screws then. I'm in a much better mood tonight - I have a cam shaft that will still do what its supposed to.

[Tanick]

Back in business. Thanks all for your help.

[Jim Richards]

Nick, with that piece broken off the end of your cam, it's going to be very out of balance. I wouldn't be surprised if your cam vibrates enough to wear badly on your cam towers and ultimately require you to replace the "top end" of your engine. Or maybe I'm just paranoid.

[304065]

That, to paraphrase the Duke of Wellington, was "a near-run thing."

But will it hold? The tension on the belt is not that great and so long as the pulleys are in the same plane my money is on it working.

Worst case, you are replacing the camshaft in a few hundred miles, but it was worth trying. Well, actually the worst case would be having to run 40IDA Webers, but one should not speak of such a fate.

What amazes me is NOT that you fixed it, but that rather, you did the entire thing without dropping the motor. I would rather drop the engine than remove the heat exchangers, given the risk of a stud snapping. Another round of Rioja is in order.

[Tanick]

John, Agreed about it only lasting a few hundred miles but it had to be tried. The belt is quite tight actually, I wonder if its too tight.

The car was fully restored last year and hit the road in May. Over the winter I changed all the seals that I could get to without splitting the block and basically did as much as I could to the engine. I just wish I'd changed those screws.

So, its been less than 1,000 miles since the heat exchangers were last off and I'd replaced the barrel nuts, other nuts and a couple of the studs. They all went back together liberally coated with anti seize so I wasn't that worried about getting the heat exchanger off. It only took 5 minutes to get off. I also removed the shock absorber but that was it. There's a lot of space between the rear seats and the engine when you take the HE off.

Jim, I'm not going to worry about the balance. I'm not sure that cams are balanced anyway and the broken bit is very close to the bearing thus minimising any movement. If you've got a 30+ year old MFI car then change the screws next time the engine's out.

[Jim Richards]

Yep, I changed all these bits (pulleys, belt, scews, washers) out when I rebuilt my engine. BTW, my belt isn't all that tight and I haven't seen one that was. Could it be that your injection pump is shimmed to make this a tight fit? Maybe a cause of your original sheared bolts issue. Food for thought.

[davidppp]

Yes, Jim..

Good point..the belt is not meant to be very tight at all..

The base of the pump is slotted to allow some adjustment..

Kind regards
David