Jackshaft - replace or not?

[martinbrowning]

I will soon be starting the rebuild of a twincam engine as part of the resto of my S130. Rebuild includes brand new cylinder head, brand new Farndon crank besides usual replacement parts - all branded new. Question is, should I replace the jackshaft for peace of mind considering it is one of the first components to go back into the block?

Haven't tried to get one yet but suspect that might be difficult. Burtons list one but the photo appears to show that it has just the gear drive for distributor and just one cam lobe for the fuel pump.

Anybody ever had one fail on them?

Cheers

Martin B

[davidc]

the 130 I've just bought apparently had one fail so for peace of mind i would.

[rgh0]

It really depends on what sort of engine you are building. You appear to be using a Farndon racing crank for a road engine with other wise standard components in the bottom end at least which is a nice but expensive option.

The jacket shaft in a twink normally suffers no wear and rarely fails. A new one is as likely to fail as an old one in good condition so I would not necessarily just replace it because I am building a new engine. You can get new shortened steel jack shafts that only have the first two bearings and the dizzy and oil pump drive gear on them and no lobes. Normally used in race engines but an option for a road engine if you are using an electric fuel pump. You can modify an existing cast iron jack shaft to the same by machining off the lobes and cutting it short at the second bearing.

I have use standard cast iron shafts shortened and special steel jack shafts in racing engines for many years and never had a problem with either.

cheers
Rohan

[alan.barker]

imho leave the jackshaft alone , it only drives the fuel pump, Dizzy and oil pump so no big load
Alan

[RogerFrench]

The drive gear on my Elan's jackshaft was worn beyond belief - maybe someone had very strong springs in the distributor points or an ultra-high-pressure oil pump.

So I reckon you need to inspect, and replace if necessary.

[JC33supreme]

I had a jackshaft fail in my S4 in about 1975 !!! I wasn't gunning it, just cruising on the M6 at about 70 mph. So I would definitely inspect very closely just in case.

[martinbrowning]

Thanks for all your replies/thoughts. I have decided to buy a new jackshaft and replace my original one - silly not to when you consider how many thousands I have spent so far.

Martin B

[Chancer]

When parts were still made by OE suppliers and subject to Ford quality control then that would have been a reasonable decision especially on a part that is subject to significant wear or prone to failure, a clutch release bearing for instance.

However with the quality of modern repro parts I take the complete opposite view, if something is original, unworn and not prone to failure then in my view its silly to take a risk replacing it with something that if you are very lucky might just fit without fettling, be made from the correct materials and to the correct tol?rances.

Distributor caps, rotor arms, condensors, rotoflex couplings, the list goes on..............

[CBUEB1771]

I see you have decided to retain the original jackshaft which seems like a perfectly reasonable decision. If you change you mind and go for a shortened jackshaft for distributor/oil pump drive only don't forget to blind the oil feed to the rearmost jackshaft bearing. This is commonly done by installing the bearing insert rotated 180 degrees from it normal position so that the oil holes do not align.

[david.g.chapman]

I have had my jackshaft out once and there was virtually no wear, and no detectable play in the bearings.

If the jackshaft has lasted OK over the years I would add my voice (for what its worth) to the keep-it brigade.

Give it a good inspection and look carefully for any cracks - though that seems unlikely.

I would change the jackshaft sprocket though if there is the slightest amount of wear.

Cheers

Dave Chapman.