Square drive tube conundrum

[NeilF]

In stripping down this CPL, I had some difficulty in dislodging the square drive tube from the end of the pinion gear shaft. However, once it was off, I wondered why it wasn't much worse; if the mild steel (?) square tube fits over the square end of the pinion gear shaft and is then immersed in salt water for considerable periods, why wasn't it a solid mass of rust? The previous one I did came off no bother, so I never really thought about it.

What is the SOP for these tubes? paint, grease? If paint, do you just paint up the inside of the tube?

The CPL's tube was welded halfway up and is blocked, and the tube is quite pitted. Is it worth replacing? Go for stainless?

[spiderg]

Neil, sometimes you hit a spot of luck with these engines. I've seen pics where they've had to use a grinder to remove the driveshaft, it was solid. I am working on two FPs, one was totally seized but the shaft was in great condition. The other was turning well yet the shaft had some hard wear on it, so it's just pot luck. I'd give it a clean up and see how it is, if it's in decent nick, give it a lick of paint (if you want) and put back in. Why go to expense if it's ok, there will be other things required I'm sure.

Gerard

[Ian Malcolm]

If you go for stainless, for heaven's sake keep the pinion end well greased as when stainless is in contact with any conventional steel alloy in salt water, the ordinary steel rapidly gets eaten by electrolysis. In fact, I'd give the mating surfaces a good coat of Duralac then pour some gear oil into the square shaft before fitting the powerhead.

Depending on the amount of wear/corrosion, you may want to end-for-end it as the top end leads an easier life. I would certainly paint it inside and out with a high zinc primer, then I gave mine a coat of Owatrol. You cant do too much painting before you put the impeller back on or it wont go on!

[electrosys]

I've had some which are 'welded on' with corrosion, and some which fall apart easily, and I've often mused why this should be. One thought I've had is that oil may be finding it's way from the lower crankcase bearing and into the square drive tube - only a small weep, maybe - but this could just be enough to keep the rust there at bay.

I've been adopting the policy of painting the outside of drive tubes and greasing their insides with salt-spray resistant grease. Won't know the outcome of this strategy for a fair few years though !

I think you may have extreme difficulty in finding the right size of replacement material - for some time I've been buying-up any lengths of drive tube (in any condition) offered on Ebay, so that I can weld good sections together to get the required lengths needed. I'd have much preferred to have bought new steel, but it ain't around. I had a good search around last year and gave up: if it ain't a standard stock size then stockholders in the UK simply don't want to know. No wonder the country's on it's knees ...

[Daryl]

I to paint the outside & put grease in the inside of the drive tube as its imposible to find that size tube here to. Probably since every thing went Metric as the orig would have been Imperial size.

[NeilF]

I think you may have extreme difficulty in finding the right size of replacement material - for some time I've been buying-up any lengths of drive tube (in any condition) offered on Ebay, so that I can weld good sections together to get the required lengths needed..

Would cutting the good, crank end half off and welding pinion and crank lengths to whatever the nearest metric section you can source make a single drive tube go further?

[charlesp]

Are spare driveshafts no longer available, then? I would have thought rather than chopping and welding a phone call to John would be the answer?

[Daryl]

Last time purchased a drive tube new in1989 here in Australia, price was $79 not real cheep back then!! So yes ive cut & shut them before.

[charlesp]

That's a lot of money! Do you mean drive shaft tube as opposed to drive shaft itself?

[Daryl]

My mistake that was the chrome tube with flange. The square drive shaft was $50.00.

[charlesp]

$50 is still a lot.

[Charles uk]

Last year a long shaft model 90 drive shaft cots me £32.69.
They probably cost more this year.

In your $ 48.25. & that doesn't include shipping I don't think your price is a P**s take.

[electrosys]

I think you may have extreme difficulty in finding the right size of replacement material - for some time I've been buying-up any lengths of drive tube (in any condition) offered on Ebay, so that I can weld good sections together to get the required lengths needed..

Would cutting the good, crank end half off and welding pinion and crank lengths to whatever the nearest metric section you can source make a single drive tube go further?

Yes - in principle - that's one of the many permutations I considered - but in practice, I think getting the shaft lined up perfectly (bearing in mind that this shaft rotates at a good ol' speed) could prove a challenge. I even bought a length of 3/8" square bar (a stock imperial size) to insert into the 'end pieces' to help align the tubes prior to welding - but I couldn't find any metric tube which was a good fit, without recourse to engineering ...

All-in-all I decided that approach was too much hassle, and that the easier option was simply to buy up old drive shafts, cut off the corroded end, and weld-up what was left.

One problem I found when trying to source steel tube was that it's not just the metric vs. the imperial size issue - it's getting the right wall thickness as well. These tubes have a very thick wall for their cross-sectional size.

[Charles uk]

The drive tube doesn't have to be 9/16" square for it's whole length, why not cut a good 6" length for the bottom end & a 3" piece for the top & insert a length of 3/8" round bar in either piece & weld it or drill & pin it.

All the drive shaft has to do is connect the crankshaft to the pinion & hold the water pump impellor in the right place, if you have doubts about the strength of 3/8 bar use 1/2" & cut the ends 3/8 square.