Jackshaft failure - last time!

[Sheepdip]

Ok - definitely lasttime I bring this up! All you engineers out there, what are your thoughts?

After a new jackshaft seizure last year with new pump, I've desperately tried to find out what caused it without success. Thoughts have been faulty pump gears but my worry is refitting used or new parts only to have it happen again. For instance.....

After laying his car up 20 years ago after pump gear failure,a colleague had just had his engine professionally and expensively rebuilt, new everything. 150 miles later the jackshaft seized. On inspection, the pump gears were fine, just the shaft seized. Fortunately the rebuilder is carrying out the work but with two failures, the chap is somewhat worried!

This has got me wondering whether the problem now is not with the pump or gears but with the jackshaft front bearing. eg Ifthe new shaft is running tight in the block andoil is not finding its way out to the rear, the gears will wear, as in my case over 1500 miles. In the meantime the shaft picks up and eventually seizes.

The shaft bearings look and measure the same, is it possible the new shaft is expanding more when hot than the old and picking up (long time since I did my engineering degree so vague)?

I know there are thoughts that theblock bearing can go oval, and lose pressure or bring the gears into closer contact but my 70kwas happily running before the rebuild with new shaft and thebearing has been checked ok since.

I'm going the route of block bushing, original jackshaft and electric pump at moment but would like to know why otherwise next time it'll be a RV8!

Have any of you with failures fitted a new shaft beforehand?

Perplexed from Suffolk.

Paul

[jbuckl]

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Re-bushing is way to go unless you can get a good block. Don't forget to check rear jackshaft bearing in the block too; smallwear there will mean a potential loss of alignment on the front bearing / skew gear(s).

Same goes for water pump lower bearing.

Clearances for the jackshaft hydrodynamic bearing are critical especially if you want to see good hot idle oil pressure!

A fully rebuilt motor but with a worn jackshaft journal will show low pressure at hot idle imho.



Incorrect chain tensioning can cause premature jackshaft bearing wear too.

The triumph jackshaft hydrodynamic bearing is about the third worst part of the engine design. Water-pump position (height) being the first & 15 degree studs being second.

Still, its a sweet unit when it runs....worth perseveringwith!

[Sheepdip]

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jbuckl wrote:

Re-bushing is way to go unless you can get a good block. Don't forget to check rear jackshaft bearing in the block too; smallwear there will mean a potential loss of alignment on the front bearing / skew gear(s).

Same goes for water pump lower bearing.

Clearances for the jackshaft hydrodynamic bearing are critical especially if you want to see good hot idle oil pressure!

A fully rebuilt motor but with a worn jackshaft journal will show low pressure at hot idle imho.



Incorrect chain tensioning can cause premature jackshaft bearing wear too.

The triumph jackshaft hydrodynamic bearing is about the third worst part of the engine design. Water-pump position (height) being the first & 15 degree studs being second.

Still, its a sweet unit when it runs....worth perseveringwith!

Yeah - that just about sums it up!

When you mention incorrect chain tensioning - what does that impact other than guides and chain? Intrigued by lower pump bearing. I fitted a new one but I was surprised at how sloppy the shaft was in it.

I'd be ecstatic (yes really) if I found it was something I'd done wrong, cause then I know what not to do next time. When it ran it was very sweet, good pressure and no noise until it suddenly stopped. And I have rebuilt other engines without problems (but they didn't get water pump or jackshaft)

[alan_thomas]

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Paul after my recent problems (stripped pump and jackshaft gears) I initially rebuilt another pump with new bearings, seal, refaced impeller etc. I really ensured it was rebuilt to the highest standard but was alarmed how difficult it was to turn just overcoming the friction of the carbon seal. I then imagined how much power this consumed at 4000 crank RPM, this means the waterpump turning at 2000RPM.
The engineer in me told me to go the external pump route and, after considering an external mechanical pump I have now bought an electric pump.
I am sure the problem with the jackshaft front bearing is linked to the load on the jackshaft. My engine is on 105000 miles and there is no measurable wear on the front block bearing despite the fact that the waterpump shaft was completely stripped from a combination of no hardening and high loads.

- Alan

[jbuckl]

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A certain member I know won't use anything but triumph original parts (rebuilt /new old stock etc) for jackshaft and waterpump.

That won't be possible forever, but removing the water pump would seem to eliminate the skew gear / loading issue and poor location (3 birds one stone) but there may be disadvantages....like not winning a concours etc!!!!

I did see2alternative water pump seals on offer with much improved load claims will post details if I can find them soon.

[Sheepdip]

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Hi Alan, I recall you were going the EP route - I probably will as well but still bemused as to why some engines run millions of miles without trouble and others don't.

I know someone who is happily running with a new (hardness checked) pump but mine failed. Also the colleague who stripped his original pump was running a 6 vane. My original was a happy 12 vane. Whats the link?

I'm surprised you found the pump hard to turn, was that installed? I'd have thought the oil pump would beharder?Also wonder why the front bearing is so large -compared to say the camshaft, maybe that indicates the force on it.

The reason for my hesitance is the original setup ran well on both my engines until I innocently changed parts. Personally I'd rather have kept that setup. Anyway Removing the pump will eliminate one factor, I'm hoping the original rather than new jackshaft will eliminate the other.

Good luck with yours.

Paul

[Sheepdip]

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As a matter of interest Alan - did your failure just chew the pump gear/jackshaft gear/bothor seize the jackshaft as well?

There could be two problems here - if as you both say the seals are too tight, coupled with a12 vane would load and wear thegears, maybe my impending jackshaft seizure reduced oil flow and caused the gears to wear?