VHPD Refresher?

[Richard Anderson]

After an unfortunate incident whereby the keyway preventing the crank pulley rotating appears to have sheared off, my dry-sumped SLR ran with low oil pressure (I noticed no warning light on, though) for a short period of time (<2mins) at very low revs, before I managed to stop.

I did notice some burnt oil from the exhaust.

 

The bolt holding the pulley on was tightened up and the engine still appeared to be running fine on the way home.

 

My question is, what would be the prudent work to have done? ...An engine refresher? ...and how much is that likely to cost?

 

A factor in my descision would be that previously the car had been used to race, and would getting a clean bill of health now, help influence the price in a positive way, should I come to sell it it the future?

[Peter Carmichael]

What finally made you stop?

[Richard Anderson]

the full story...

 

I went for a run just before Christmas, and luckily was just trundling along gently when I heard a strange rattling sound at some traffic lights. I pulled away gently and then just down the road the alternator light started coming on. I stopped at the first available opportunity some 300m or so down the road and got out to have a look with the engine still running. I took the bonnet off and saw that the bolt holding the crank pulley on had come loose and the pulley was just about to come off. I switched the engine off immediately but not before noticing some burnt oil coming out the exhaust.

 

I called the AA man and he came along and tightened and locktighted the bolt. We done a quick damage assessment and we could see that if I had stopped a moment or two later the timing belt which is being held on by the pulley would have jumped off! There is a keyway which prevents the pulley rotating and this had sheared off but, I suppose it is impossible to tell whether it was the bolt that came undone and sheared the keyway or the other way round. Initially I was suspicious of some work I had done on the car (a new starter motor) a week before but, I can see no reason why they would have undone the pulley to do the starter motor.

 

Well, the engine turned over and started just fine, and on the short mile or two journey back to my house I could hear nothing wrong with the engine.

 

I am just about to send the car to Roger King, having saved up some money, to have it repaired but, my question to you is : what should be the extent of the work I have done?

 

Would it be prudent to have an engine refresher at this point? ...or should I limit it to a new, timing belt, keyway, and some external checks?

 

It is such a shame, as the car was running beautifully, and I know that the engine was in great condition as I had it checked on a rolling road a month before the incident.

 

I would be very grateful of any advice you had to give!

 

[Peter Carmichael]

OK. Got to work out what happens when the pulley comes loose that lets burnt oil come out of the exhaust.

 

As you no doubt know, the pulley drives the scavenge belt, so with the scavenge disabled or working less efficiently than it should you pumped the dry sump tank dry and filled the engine with oil. The piston blowby gasses were also not being sucked out of the crank case by the scavenge pump.

 

Having an empty dry sump tank also means that the pressure pump would eventually run dry and the bearings would not get lubrication. Under load this would be catastrophic within about 2 seconds; at gentle loads you are relying on luck. It looks like you got away with it purely from the fact that you drove away from the incident.

 

So where did the oil come from? Well, if you pumped the engine full of oil, both the head and the sump are going to retain oil. It is possible that the oil build up in the head could lead to the valve stem seals being totally immersed and unable to deal with the oil - unlikely though. What I don't know about your engine is how the breathers are configured. The cam cover has two pipes coming out of it on the induction side. Sometimes these are blocked off. Sometimes they run to a catch tank. Sometimes they run to the filter backplate. If you can trace these pipes and tell me where they go I may have an answer for you.

 

Regardless of why the oil smoke appeared, I think you got away with it. Roger King is the sort of person you can trust to find things and not lead you up the graden path paying for extra work that is unnecessary.

[Gridgway]

Hmmm, your story Richard is strangely reminiscent of my rather more expensive R500 engine failure. In mine the crank pulley did actually come off on track which simply toasted the engine. The interesting part is that we think we traced the root cause to when it had starter probs! The car had several starter motors replaced and eventually a new flywheel (no idea why). When the engine was taken out and split from the gbox after the failure, the flywheel fell off and the bolts holding it on had disintegrated. The trail (as they say) went cold at this point, but it is perfectly possible that a 'loose' flywheel vibrated the crank pulley bolt out. This may all be coincidental, but you may well want to look at the other end of your engine before deciding all's well.

 

I did have a few other symptoms before the failure that in retrospect definitely appeared as the engine was falling apart. I had a nasty missing at about 5k rpm as I assume a resonance was set up with the loose flywheel. I also had troubles with smooth low speed driving. The engine was all over the place in second gear pootling along. I either had to accelerate or take my foot off the gas, part throttle was orrible.

 

A lot of conjecture here and rather way off the 'PC' standard of analytical diagnosis, but we can't all be geniuses(!).

 

Graham

[oilyhands]

If the sump fills with too much oil, windage will splatter the bores with more oil than the oil control rings can deal with...

 

Oily

[Richard Anderson]

First, thank-you for the response guys..

 

Peter : As far as I know I have only got a breather coming out of the oil tower (as per the 750 MC regulations? ...forgive me, if this is not the breather you mean, my mechanical knowlege is quite limited)

 

Graham : Interesting about your starter motor problems...my engine showed no symptoms of running badly before the incident...but, I did have to push-start it a number of times when the previous starter-motor was if the process of failing....I don't suppose the jolt on the engine of starting it in this manner could have been a contributary factor????

[Richard Anderson]

One other thought : There is no proceedure whereby you lock a spanner onto the crank-pully to prevent the crank turning while replacing a starter-motor is there?

[Rob Walker]

I can`t see any reason why you would ever want to lock the engine when changing the starter motor.

[Gridgway]

Richard, it is possible that bunp starts had a contributory effect if indeed your flywheel is loose like mine was, but it's pretty tenuous. The shocks that need to be applied by the transmission to the flywheel are pretty extreme to dislodge a flywheel. Examples would be a race car curb hopping or accidentally changing from 6th to 3rd. So the sequence of events is shock to flywheel, loose flywheel, vibration making the bolt come out the crank pulley, not very likely in your case I think. Only way to find out would be to split engine and gearbox. Prob not worth it.

 

Graham