'55 Square Four engine strip.

[tomwalker]

I thought I was maybe wasting my time stripping the engine just to check the sludge traps because it all looked so clean and nice.

Now very glad I did! Both plain mains damaged, and one has turned and moved inwards.

[tomwalker]

Have removed the crank drilling plugs and both traps were plugged. The worst one was blocked almost to the journal drilling.

[Bob.Murphy]

I'm afraid that's the way it is - I used to strip my Square Four every year and clean-out all the sludge traps.

I changed the oil every 1,000 miles as well !

I'm glad you caught it before something seized & broke.

Bob.

[paul.jameson]

A fine illustration of why it pays to strip a Square Four before use if its history is unknown. Do you have an external oil filter fitted? Have you any idea when it was last stripped?

All the brown marks inside your cases are carbon deposits which will slowly be washed off by the detergents in your oil and will be held in suspension within it until removed by the external filter or deposited in the crankshaft sludge traps, particularly if no filter is fitted. So clean all internal engine parts as much as you possibly can before re-assembly.

[tomwalker]

Thank you for your advice, I hope you will be kind enough to follow on because there are and will be other detail things I need help with.
John Bebb kindly sent me his puller/pusher set for the coupling gears.
I dont know when the engine was last stripped, the previous owner, a friend, was unaware of the mechanical needs of a Square Four, or its service history. I fitted an oil filter as soon as I took the bike on, which is very much shutting the stable door after the (iron) horse has bolted!
I am wondering,
the front timing side bush that turned was 0.020" off being seated against its flange. There was no end float on that crank not surprising. interference
Do I need to arrange to secure the bushes? I have been using the forum search, and I think my machine, as a 1955 model, is just before the main bearing bushes were secured by Ariel with grub screws?
If I order new bushes from Draganfly, do they come with an undersize inner bore that needs to be inline reamed?
Should I be careful with the fit of the bushes such that the hole in the crank case and the OD of the bush gives the correct interference fit? I cant find a reference anywhere for that figure. No doubt the cases need to be heated which would mean I couldnt Loctite them in?
Thank you in advance.

[nevhunter]

There would be specified interference fits for the Bushes in the case and the allowable range would not be much. It's also likely with a used motor the Bore in the crankcase will not be quite true I would use an interference of about .0015". A bit more if you can arrange for the case to be about 150 c and the bush cooled by dry ice and fitted quickly. The whitemetal is quite soft and easy to bore and doesn't have a big running clearance like copper lead does or it will hammer and bits will come out of the metal as it has done in this case which is fatigue rather than wear. Nev

[Roger Gwynn]

Instructions on fitting the t/side bushes are on Draganfly's page https://draganfly.co.uk/product-categor ... d-1937-58/ Grub screws can be added and were used 1937-48 and again 1956-58. The 1956 bushes can be used in earlier cases, but note that they have a larger diameter flange all the better for fitting an anti-rotating peg but the flange is 3/32" thick instead of 1/16". Bushes with an oversize OD are also available.

[tomwalker]

Thank you very much indeed for the useful information.

[paul.jameson]

The 1937-47 timing side bushes were secured by grub screws which go in from underneath the bearing on the outside of the case. You fit the bush first then drill it to suit the grub screw. This is not easy to get right as over drilling will result in deformation of the white metal at best and probably a scrap bush. So in 1948 Ariel gave up on the idea. The 1956 onwards system uses a pin in the flange of the bush from the inside of the engine. This ensures that the pin cannot come out and anchors the bush in place effectively. But you do need the pins in the correct places or the oil feed holes in the bushes will not line up! (The earlier bush has a groove round the outside which overcomes this problem.)

I have had timing side bushes come loose (in my first Healey) without damage to the engine but I was running a Morgo pump and the oil pressure warning light told me something was amiss. Either an oil pressure gauge or an oil pressure warning light can be a wise addition to a Mk II which has neither.

When replacing the bushes I turn them in the lathe so that they are about 5 or 6 thou oversize on the journals when fitted. Then I line ream then to size. If you miss out the lathe step, it takes all day to do the reaming !

Keep asking for advice as necessary as you proceed. The really good news is that you don't have to start by finding some replacement crankcases due to a blow up.

[tomwalker]

Great post Paul, Im very grateful that such a super resource as this forum exists. How on earth did keen owner/fettlers manage before?? Many hours ear wigging on the blower no doubt.
Currently struggling to get last drilling plug out. It is a counter sunk hex drive screw, punch pegged. It would not budge, and I have mashed the hex hole, so now drilling the bloomin thing out and hoping to pick the remains of the thread out.

How do you line bore the bush? My brother has a king pin reaming tool, so I kind of understand the process, but do you need special kit or make something up? I noticed Drags advertise a service, but was hoping to crack on with it over the holiday.