jackshafts and external water pumps

[Rubce]

Hi All

There are occasional horror stories of waterpumps and jackshafts seizing etc resulting in severe and expensive engine damage. Please excuse my ignorance on this particular area of a Stag but if the original pump is replaced by an external belt driven or electric one, does that completely remove the jackshaft issue? Am I right in thinking that the original pump is driven off the jackshaft which in turn is powered off the distributor shaft? If the original pump is removed does the jackshaft remains in place doing nothing other than spinning round with no load on it?

Sorry to be asking what is probably a load of stupid questions but I just want to get in clear in my head what benefit an external pump would give me.

Thanks

Bruce

[jleyton]

Hi Bruce,

Jackshaft is driven by one of the camchains and the water pump and distributor are driven directly off it. The oil pump is driven off the bottom of the distributor drive.

So, if water pump is omitted (a brass bung is available and should be fitted in place of the pump) the jackshaft is still powering the distributor and oil pump.

Cheers

Julian

[Rubce]

Hi Julian

So the jackshaft can still fail and take the engine with it from lack of oil pressure etc? Or is it the water pump seizing up which causes the jackshaft to fail so removal of the waterpump removes the jackshaft failure risk?

Cheers

Bruce

[GDPR]

Lack of oil pressure would probably take the crankshaft out before the jackshaft... but if the timing chains are done badly, you could damage the front bearing of the jackshaft and that could cause a failure...but water pump skew gear failure is the prime cause...

[Sheepdip]

As a sufferer, I've gone for a STAGDAD external belt pump and its good. The only downside I've come across is leaks from the myriads of hoses on my setup but it got me down and back from Italy. Sure the jackshaft still drives the oil pump and disi but much less of a load, the bush in front of block seems to be working although oil pressure is a tad lower than I'd expect and like. Why it fails is still a mystery as I've known them fail on a rebuilt engine with less than 500 miles to many thousands. My personal theory (as Kryten alluded) is problems with the timing chains, having looked at Tony's video I now know I tended to overtighten them, also talking to EJWard, a commonality of failure was after "front end work". There were some dodgy pumps around I'm sure but mine was cerificated brand new and had a hardness test certificate.....hence my viewpoint.

[V Mad]

In the past soft water pump or jackshaft gears were probably the most common cause, but I havent heard much of that lately.

Aftermarket oil pumps with high pressure outputs are probably the main culprits now. Timing chains are tensioned hydaulically ie by the higher oil pressure which puts a higher load on the timing chains, this in turn puts a higher side load on the jackshaft at the front which could cause bearing failure, and then siezure.

[flying farmer]

Having had the water pump/jackshaft seizure issue on my stag a couple of years ago, I put a poll on the forum about snapped timing chains and IIRC 75% of snapped timing chains followed jackshaft seizure. The remaining 25% were don't knows or total neglect.
The jackshaft only has a front and a rear bearing. I have never heard of any problems with the rear bearing, even if a high pressure oil pump has been fitted, it is normally the oil pump drive gears that wear out first.
The front jackshaft bearing is two or three times the diameter of the rear bearing, and fed directly from the main oil gallery, so lubrication should not be a problem. Bear in mind the camshaft has a smaller diameter bearing, further away from the sprocket, and is fed by pressure reducing flats on the jackshaft, and this is not prone to seizure either.
I can only assume that the combination of driving both the oil pump and the water pump puts a significant load on the jackshaft, and if you factor in overtightened chains as well it can overload the front bearing to the point of failure
Neil

[Westfaling]

I had a jack shaft seize up at the front bearing. It snapped the bolts to the cog, chains were still intact. No issues with any of the teeth on the drives. I've always assumed it was lack of oil pressure at the front bearing, insufficient lubrication causingg overheating and seizure. Car had been stolen and was being thrashed at the time.
Nick

[Sheepdip]

I had a jack shaft seize up at the front bearing. It snapped the bolts to the cog, chains were still intact. No issues with any of the teeth on the drives. I've always assumed it was lack of oil pressure at the front bearing, insufficient lubrication causingg overheating and seizure. Car had been stolen and was being thrashed at the time.
Nick

Lucky outcome then (altho reckon you didn't think so!) IMO I'm not convinced water pump gear failure is causing the jackshaft bearing to seize on newly rebuilt engines, why should it even if metal shards are flying around? I think its the other way around, jackshaft front bearing starts to seize, no oil splash to the water pump gear so that starts to break up. I think power consumed by high pressure oil pumps could have an affect - remember the twisted drive rod? However with a rebuilt engine and oil pressure of 50psi, certificated pump, new jackshaft, 500 miles in a friends and 1500 miles in mine, what other culprit could there be? There are hundreds of thrashed Stags happily running on 100k+ worn engines with original bits. However removing the gear driven water pump can only help.

[nib]

When I changed a cyl head over the other year the top sprocket was being a pain to come off the cam,as I moved it from side to side at one point it must of given the effect of the chain going loose which in turn sent the tensioner out,when I came to put the head back on it was as tight as a guitar string so I pulled all the timing cover casing off and reset the tensioner so it wasn't as tight.Im glad I took the trouble to do this as I have heard a few people say they thought jackshaft failure can be down to overtightened chains.
Mark

[Sheepdip]

Well thats my theory Nib, just based on personal knowledge, I'd be happy to be shot down by someone who can prove how it happens as its an unpleasant experience. All I know is that now I err on the slack rather than tight side and to date with 2 rebuilds (and fingers crossed), no problems with an internal and external pump. I'd be suprised if you'd have been able to get the cam back on tho - been there . I also made the mistake once of taking the bottom pulley off then timing the engine on one of the cams before replacing cams and chains. ok so whats the problem with that? Due to a knackered bottom sprocket (overtightened chains?) the chain had slipped a cog and I retimed it all out of place.......it ran ok and no damage but just felt sluggish.