MFI Cam Pulley - a slight problem

tanick · Post by **tanick** » Sun Aug 13, 2006 11:21 pm

A quick question, I'll go into the full details later but suffice it to say that I'm now in the Uk and my car's in France.

What does the MFI pulley on the end of the cam shaft screw into? Is it the camshaft or is there another part between the two? I would have thought the end of the cam was splined and fitted into another part but from my quick research it looks like the 2 screws and 2 roll pins go straight into the camshaft. How much load is on the MFI belt whilst driving?? Its easy enough to turn when the fuel pump isn't running but when the pump is actually presurising fuel is it much tougher?

I am beginning to think my summer's driving is over.

johnM · Post by **johnM** » Mon Aug 14, 2006 2:02 am

Hi the pulley is secured into the end of the camshaft with 3 screws, the belt need'nt be too tight and the pump will be quite easy to turn.

Regards John

Nick Moss · Post by **Nick Moss** » Mon Aug 14, 2006 8:05 am

The camshaft pulley is attached with 2 M6 x 15 cap head machine screws. The pump pully is attached by the same size screws, but is slotted to alloy timing ajustment. As John says the pump should turn freely. Don't despair. The pump can sometimes be freed off by removing the side plates and carefully lubricating and freeing off the pistons. Is the pump getting its proper supply of oil I wonder?

tanick · Post by **tanick** » Mon Aug 14, 2006 11:22 am

The full story: I went over to France this weekend and pulling away from Calais noticed the engine was missing slightly under load. I took this to be maybe dirty points again like I had in Le Mans and carried on. The problem got progressively worse and became quite regular, like a drop in power every 2 seconds or so. I figured I'd limp to my destination and 12 miles from it the engine stopped and wouldn't start again. I cleaned the points and tried again. Pulled out a plug and checked for a spark. It was fine but I noticed the plug was dry despite a fair amount of cranking. Pulled the fuel pipe off the injection pump and cranked again. Lots of fuel getting to the pump. noticed the injection pump belt was a bit slack so I reached round and turned the top pulley by hand. It turned freely and caused a squeeking at the lower cam pulley. Not good because you shouldn't be able to turn this by hand if all is well.

So I jacked and propped the car, removed the n/s rear wheel and removed the bolts holding the cover of the cam pulley. I simply pulled the pulley off the end of the cam - it was only held on by friction, hence it was slipping - and found one of the hex bolts in the bottom of the cover, I think the other dropped onto the heat exchanger out of sight.

I set the pump timing and then triet to re-attach the pulley using two of the M6 bolts from the engine tin packed out with washers. After about an hour of fiddling in what must be one of the least accessible areas on a 911, I realised that the original bolts had sheared off and were still embedded in the end of the camshaft. At this point I accepted defeat (not graciously!)

So, I'm not sure where I go from here. When the car is re-patriated what do I do? Do you think I can extract the broken bolts once I get the heat exchanger off or am I destined to have to drop the engine and remove the camshaft? I'm not looking forward to this

My question about the force required to turn the pump is because I changed the belt and the pulley on the pump when the engine was last out and the pump pulley was very free. I wondered why these bolts would shear if they aren't under much load. I changed almost every fastener on the car but not those. Damn.

Lightweight_911 · Post by **Lightweight_911** » Mon Aug 14, 2006 12:14 pm

Nick - sorry to hear of your troubles...seems like your car doesn't like going to France !

With regard to the mfi cam pulley problem: you say that the pulley was slipping - what happened to the 2 roll pins ?

You also said that you found one of the original 'hex bolts' (they should be M6 cap-head allen screws as Nick stated) when you took the cover off - was there any indication that this had sheared ?

I would be surprised if the fasteners had sheared...

tanick · Post by **tanick** » Mon Aug 14, 2006 12:39 pm

Here's a photo of the culprit taken while the engine was out, before I changed the belt. The only part I have is one of the screws which was broken leaving about 8mm of threaded part left and a washer.

Something else did drop onto the heat exhanger but I couldn't find it. I was working in half light and the car was on gravel. I didn't see either of the roll pins but from the picture it appears they were there. I stupidly didn't take a pic of the end of the cam on Friday but you could just see the sheared bolts inside about 2 mm from the surface. I'm having trouble understanding why they would shear, the pump still turns freely. How the hell am I going to get the remains of the bolts out of the cam without dismantling the heads?

Alan @ CanfordClassics · Mon Aug 14, 2006 12:43 pm

Sorry to read about the car problems Nick.

To shear both bolts on the Cam pulley would take some pressure, more than the MFI belt would stand. But, I suppose if you have seen them still embedded in the cam then they must have.

Working on from there, I am sure you will need to take the cam out to repair this, but I would still want to know what causes this to happen. You don't need to dismantle the heads but you will need to take all those rockers out on that side.

Good luck

Alan

Gary71 · Post by **Gary71** » Mon Aug 14, 2006 1:12 pm

Sorry to hear your troubles Nick

, hope you get your car back soon.

My theory for the broken bolts! (for what it's worth!):

1. Bolts undertorqued, or maybe missing threadlock? Once they start to come loose the drive is transmitted through shear on the bolts rather than through the clamping friction of the pulley on the end of the cam. Eventually one of the bolts fatigue fails, overloads the other and the roll pins.

2. The bolts could also have been over tightened, causing a partial failure in the thread, leading to the same end failure mode.

You may be able to drill out the remains of the bolt in situ, but to me it sounds like it needs to come apart to make a proper job of it and not risk the camshaft / engine.

Good luck

tanick · Post by **tanick** » Mon Aug 14, 2006 5:48 pm

What srikes me as odd is that the pulley was slipping for a long time. Even when it finally stopped working the pulley was still on the camshaft as I could hear it squeeking when I turned the top pulley. The whole thing doesn't add up to me. Anyway, I'll take the heat exchanger off when it gets back and have a good look and post some pics.

Now all I've got to do is work out if I want to try and do the work myself or pay a pro for the pleasure.

davidppp · Post by **davidppp** » Mon Aug 14, 2006 5:53 pm

Hello there.

I'm with Gary on this re failure mode..FWIW...but I would reckon on repairing this without much stipping at all.

Even may be possible in situ.

Much eaqsier with engine out of course..

The broken ends will nto be jammed tight..unless they were too long to start with and bottomed in the holes?

So a left hand drill is likely to work, with lots of lube..or drill for a Snap-on insert....again I have amny times been able to substitute a spline driver bit for a electric driver..nice hardened steel..

If this fails for any reason, the next ploy is to drill and tap new holes for the allen screws, and of course for the Spirol pins..the can is only cast iron and although chill-hardened should drill Ok ..
I can't see much to be gained by stripping the top end..

See, I'm not always gloomy!

Curmudgeonly , but Kind regards
david

tanick · Post by **tanick** » Mon Aug 14, 2006 10:48 pm

Cheers for the kind words and help. My car's outside in all this rain at a Ssangyong/Daihatsu garage in deepest darkest Champagne at the moment. If it gets back in one piece I'll post some pics and let the experts diagnose further. I'm just glad I put some polyurethane sealent round the screens a few weeks ago.

tanick · Post by **tanick** » Wed Aug 23, 2006 5:18 pm

David, I've been checking this out and I agree with your thinking about the screws not being too hard to get out. As soon as the car gets back I'll soak the exhaust nuts and the sheared screws with plus gas. Luckily the exhaust only went on 3 months ago with plenty of antiseize so shouldn't have issues getting it off again.

The screws look original so shouldn't be jammed, maybe loctited though so I'll use some heat. I'm thinking of ordering a set of snap-on left handed cobalt drill bits and a set of their screw extractors. About £80 worth of kit but a lot easier than removing the cam. Do you think I'll succeed? Is there a better brand of tools for this sort of stuff? I want quality as I don't want snapped bits in the end of the cam!

Alan @ CanfordClassics · Wed Aug 23, 2006 6:08 pm

The snap on screw/stud extractors are very good, much better than the ones which grip and mark the thread. If they are the same ones I have, the snap on ones use a collet which screws onto the thread and then grips it.

Good luck

Alan

davidppp · Post by **davidppp** » Wed Aug 23, 2006 7:25 pm

Hello, Nick, Alan.

I think the set Nick is buyin are the ones with little splines you tap into a hole drilled in the broken bolt..they are brill..miles better tyhan the crappy easy-outs which always result in a sparek erosion job!

And if all fails drilling new holes is not going to be difficult..

I'd bet they come out tho'

Good luck
David

tanick · Post by **tanick** » Wed Aug 23, 2006 8:22 pm

Well I meant this type as they look strong http://buy1.snapon.com/catalog/item.asp ... ir=catalog but then I saw this kit:

http://buy1.snapon.com/catalog/item.asp ... ir=catalog

any suggestions? Not sure about the difference between spiral flute and tapered bits.