Which broke first?

[flying farmer]

Whenever you read about the Stag engine in motoring literature one of the main things they bang on about is timing chain failure. In the time I have been using this forum I can recall very few timing chain failures except those caused by neglecting to change them at the proper intervals. However there seem to have been quite a number of jackshaft seizures caused by dodgy water pumps which is something I have never seen mentioned, normally just the failure of the pump is mentioned.
I have decided to add a poll for those like myself who have suffered engine damage through broken timing chains.
1 The chain snapped first, this includes tensioner failure (due to neglect)

2 The chain snapped with no prior warning (still within the recommended mileage)

3 The jackshaft seized and cause the chains to break

[GDPR]

Happily, my vote which was option 1, has not happened to me on my Stag, but I am including myself as it has happened on a close relative with a similar setup - Dolomite 1850

[flying farmer]

Happily, my vote which was option 1, has not happened to me on my Stag, but I am including myself as it has happened on a close relative with a similar setup - Dolomite 1850

I have had a water pump/ jackshaft failure on a dolly sprint engine but haven't included it as it didn't get to the point of seizure. I heard it rattling at tickover and investigated. I have not heard of a stag pump rattling and suspect that the smoother tickover of a V8 will mask the problem. My thinking is that the crank of a four cylinder will not be rotating at a constant velocity at tickover, rather increasing and decreasing in speed as compression and firing strokes take place, and this led to the pump gears chattering due to the extra free play

[Another Peter]

I know that this might be the "kiss of death" but none of them have broken (yet) in my 5 months ownership....

Regards

Peter

[GDPR]

Patience, Peter..... there is still plenty of time....

[Rouseyboy]

I wish you had added an option "Do you have no idea when your timing chain was changed if ever". That is the one I would have voted for!
When is the recommended interval for this job?
My car is 70K miles, but I have only owned her for 3 years and added about 7K myself.

... Dave

[GDPR]

General consensus and good sense says 25000 miles, although I have seen original chains hit 80000 without problems.....

Russ

[tonypy1]

Perhaps some chains snapped due to overheating problems in the past i.e. a head warped, the bottom face was skimmed but was refitted without checking how freely the camshaft rotated in its bearings..?

[flying farmer]

Well, it looks like my thoughts on timing chain failures were well founded, with 75% of supposed timing chain failures being caused by the jackshaft seizing first.
The good thing is the small number of neglect related failures ( and that was on a dolomite 1850 which is mechanically the same). That should be good news for those fretting about their timing chains, and those who have purchased a car in recent years that do not know its service history (shining a lamp down the oil filler hole at the one visible timing chain tensioner is a good guide as to how far things have stretched)
That just leaves the question of why so many jackshafts seize. Water pump failures are obviously a major issue, but someones comment on another thread that E J Wards reckon a lot of failures happen shortly after timing chain work, suggests that maybe a better quality timing chain and less frequent stripping and rebuilding would reduce the incidence of failure. I think that the old saying of "If it ain't broke keep fixing it until it is" may have a degree of relavence here
On the last couple of engines I have built I have used L D Parts JWIS chains in the hope of extending the rebuild interval. Unfortunately I now have so many cars on the road that I will probably run out of lifetime before I wear them all out so I will let you all know in twenty years wether this was a good idea or not!
Neil

[jleyton]

That just leaves the question of why so many jackshafts seize.
Neil

Hi Neil and others,

Thanks for giving me further reason to feel even more paranoid about my Stag

Of course, if/when this happens to you it's devastating but, so far (famous last words ) , I've not yet had this problem on the two Stags I've owned. So, how common is it ? Obviously everybody on here who has had it happen will report on it because it such a cataclysmic occurrence but, as with the newspapers, bad news makes news whereas good news doesn't. I think we'd get fed up if most of us posted on here to say 'another day without a jackshaft seizing'

So, without detracting from the awful occurrence of a jackshaft seizing for those of you who have been unlucky enough to suffer, do 'so many jackshafts seize'? And what are the chances of it happening to me? 1 in 10, 1 in 100, 1 in 1000 ? I know it's impossible to be precise but I just want to get a feel for how common it really is.

All thought gratefully received.

Cheers

Julian

[Staggard]

I read into EJ Wards statment ( jackshaft failure followed chain replacement ) to mean when the chains have been replaced the tensioners have been racheted out and tightened the chain's up like bow string's thus pulling the jackshaft off centre and hard against the side of the front bearing reducing the ability for oil to pass between the two surfaces, so through lack of lubrication and heat build up sizure occures, not unlike overtightening a belt w/pump or alternator it loads up one side of the bearing and knock's it out. Graham

[singapore stag]

Good point staggard,..The "right" tension is paramount in chain replacement.
Sukh.

[Ian Durrant]

That just leaves the question of why so many jackshafts seize. Water pump failures are obviously a major issue, but someones comment on another thread that E J Wards reckon a lot of failures happen shortly after timing chain work, suggests that maybe a better quality timing chain and less frequent stripping and rebuilding would reduce the incidence of failure. I think that the old saying of "If it ain't broke keep fixing it until it is" may have a degree of relavence here
On the last couple of engines I have built I have used L D Parts JWIS chains in the hope of extending the rebuild interval. Unfortunately I now have so many cars on the road that I will probably run out of lifetime before I wear them all out so I will let you all know in twenty years wether this was a good idea or not!
Neil

I think E J Wards and you are right. Over tensioning of the chains (not using the right size c shaped washer and the feeler gauge and then also perhaps levering on the chain guides when tensioning) do place a load on the jackshaft that it can't handle. However I think also there are still some dodgy pump shafts about that break up and cause metal shards to get into the jackshaft bearing and cause it to seize.

For me the IWIS chains are worth every penny. Just fit them and you will probably never have to do a chain change again.

[flying farmer]

In answer to Julians question of what are the odds of a seizure occuring, I suppose it depends on how many stags are on the road. We seem to get a couple a year appear on the forum, but of course people who would never normally post when all is going well, are straight in asking for advice when it all goes wrong. There are probably more we don't hear about as the owners have no mechanical knowledge and just get the car towed to a garage, and their life savings dragged out of their wallet!
I would hazard a guess that in any given year the chances of a failure occuring are probably nearer one in a thousand than one in a hundred, but throw in a change of timing chains and a water pump fitted in the 1990s as mine was, then the odds are probably worse than one in a hundred. If you have got an old pump with unhardened teeth it will fail at some point, wether it causes a jackshaft seizure will be very dependant as to what happens in its final moments. I have a suspicion the seizure on my car would not have happened if it was a MOD rather than an auto simply because the engine was spinning at 4000rpm on the motorway when it let go. Currently with the overdrive box and 3.45 diff it turns at 3200rpm at the same speed which would lower the loads considerably
Personally, I never make any allowance for the age of a car when I drive it, if there is a red line on the rev counter then it will be visited regularly, particularly when overtaking, which is why I have a rev limiter fitted to the Stag and the Stag engined TR. I work on the basis that if it goes bang, then it was going to go bang anyway, and all I have done is make it happen a bit earlier
Neil

[Stagdad]

I never make any allowance for the age of a car when I drive it, if there is a red line on the rev counter then it will be visited regularly,
Neil

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