SQ4 Small End Bush Missing

[DaveH]

Hello all,

I'm tearing down my 1952 Mark I Square Four, taking arms against a sea of troubles, and have noticed the small ends have no bushes. The gudgeon pins, of standard diameter, run directly in the rod alloy. This seems odd, and I've never before seen such an arrangement. Also, I see a small end bush listed in the parts catalog (1131-37) - though it's unclear which years use it.

Are these original rods, or perhaps aftermarket? As one of the pins has excessive clearance, is there any reason not to machine out the small end and install a bronze bush?

Dave

[nevhunter]

Good alloy is fine in that application. Just fit oversize pin of the same weight. Nev

[DaveH]

Nev,

Thanks, I can see that working. But it requires locating an oversize pin (where?), machining both the small end and piston bosses to fit, then possibly lightening the (hardened steel?) pin. It would be simpler to just enlarge the small end and install a bush, as Ariel apparently did on some Square Fours; perhaps just as good?

Dave

[nevhunter]

It would only need to be about .003" oversize. Easy to Make a pin that size from a batch and you don't need to remove the rod to machine it and worry about the bush moving in the alloy which happens and the bush will affect the Balance also. Nev

[david.anderson]

They look like standard rods to me. There was no little end bush in either the mk1 or the mk2. There is no little end bush in the AOMCC rods either, and there is no need for one. If the little end has excessive play in your mk1 rods then I would suggest that they be replaced asap. Worn little ends would suggest a very high mileage which would mean fatigued rods. All aluminium rods have a service life/duty cycle irrespective of whether they have been subject to high revs or not, so I would replace them if there is any sign of wear. And being cautious I would fit the AOMCC rods no matter what.
David

[simon.holyfield]

Don't all square fours have small end bushes? Mine certainly does.

[nevhunter]

I think all the originals have bronze bushes The same with the 500cc Twins. One of the Bronze bushes of MY 500 TWIN was loose in the rod end. The other may be too. Small ends get very hot. The engine was STD bore and never been sleeved so MOT high miles. SOME AJS/Matchless have a Dural bush in A STEEL ROD. It's a very satisfactory Material for the Purpose There's a lot of difference in the thermal expansion rate that might promote looseness with ALLOY Rods. NEVER use BRASS. it's got ZINC in it and it's a lousy Bearing metal. Nev

[david.anderson]

Simes
The mk1s that I have seen do not have small end bushes nor did my mk2. I also had a pair of mk1 rods that I gave away that were not bushed. I hope that I am not so unobservant to have not noticed bushes. I initially purchased those mk1 rods when trying to source mk2 rods some 20 years ago when rods were scarce so i took what I could get. Unfortunatley the person that I gave those rods to John Shanks has passed, and I know they were not used. However having just spoken to a friend with a mk1, his rods are bushed and he believes they were from original.
David

[Simon.Gardiner]

Well, I don't know what the situation is in Texas but in the UK if you could even find someone who was prepared to make you one new gudgeon pin (to the correct weight), and bore the pin holes in the piston, and check the little end for roundness and resize if necessary, you could probably buy quite a few sets of brand new conrods for less money!

As has been said if you've got original rods you ought to be looking to replace with new anyway. You were expecting a world of pain...

SG

[DaveH]

Thanks for all the informed input!

It seems uncertainty remains on whether small end bushes were original fitment; on the one hand they're shown in the factory spares list and many people have observed them, on the other hand many have observed likely original rods without them. Perhaps some of each type were supplied by the factory. Anyway, I'll most likely have the small end machined for a bush (1131-37), as that would be less of a project than trying to locate and deploy an oversize pin.

Of course no need for a bush if I replace the rods, which I'll need to consider. The arguments against doing that are the expense (£1,075) and the fact that they're on back order at Drags.

PS - Based on discussion at the Drags site, it seems my rods are not original to the Mark I, but are the 1955-on style with two ribs and BSC threads. These are said to be stronger than the earlier design.