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MG Midget and Sprite Technical - spiggot bush

Hi Chaps,
Have finished the engine rebuild and the gearbox has come back from the re-conditioners. Now it's time to put the two together..
to make sure that I don't have to take things apart again I am thinking of replacing the spigot bush.
(I should say that the engine is a 1275 marina unit)
I have had a feel around in the back for the crank and there seems to be a bronze bush in place (although it is hard to see and I thought that marnina's had needle rollers). Using some drill bits to get bore size for it looks like it is near 12.8-13 mm inner diameter.
checking the input shaft of the gearbox it is 12 mm making me think that the spigot bush is worn.
I had mistakenly ordered a needle roller bearing which looks to have an OD which is too wide to fit in place of the bronze bush. Is this correct that you cannot substitute one for the other without drilling the crank?
Interestingly the new needle bearing spigot also seems loose on the input shaft (has an inner diameter of about 12.6-7 mm) for most of it's length with a tight fit only at one end which seems to be an oil seal.
So now I am thinking that the existing spigot bearing may be within tolerance.?
the worry in the back of my head is that the Marina 1275 doesn't fit a ribcase 'box without some form of crank modification (additional to having the end turned down for the flywheel). This would mean taking the engine apart!
So questions are:
1) what should the inner diameter of the spigot bush be?
2) can I replace bronze with needle without drilling the crank?
3) does a marina engine spigot fit a ribcase?
4) how easy is it to remove a bronze spigot?
Cheers
tim
T Dafforn

Tim

I too have a Marina engine mated to a ribcase. I also remember spiggot confusion when I came to mate the 2. But I cant recall the exact details !

Looking through my bills I had ordered a 1A1559 (Flywheel bush) prior to the build and later an AHU1026 (Flywheel Bush roller) at a date that corresponds to the final build stage. I cant say with any certainty though which once was actually used. I had a spreadsheet of notes but I haven't written anything down about bushes.

I definitely had the flywheel machined to the crank - but nothing on either crank or input shaft.

So....I'm sure its possible but cant tell you what combination is needed. Helpful eh ?

To remove the bronze bush fill the end with oil and push/tap and close fitting drill bit end into the bush. The hydraulic pressure behind the bush is supposed to pop the bush out.

Dean Smith ('73 RWA)

Tim,
I don't have experience of what you are asking, so apologies, this is just a bit of speculation.
- If the needles in the bearing float a bit in their cage this could explain why they appear loose on the input shaft. But if they are bunched inwards so that they are a close rolling fit on the shaft, then the OD maybe will fit into the crank?
Guy W

Question 2. "can I replace bronze with needle without drilling the crank?"

Yes you can.

Although I don't have your combination, I have replaced the bronze with a roller, and I didn't have to drill the crank. Mine is a 1275 sprite engine/crank, couple to the shaft of a Ford T9 box.

I could measure my spare crank if it will help. I have no idea if the marina uses the same size spigot bush, but why would it be different, since it worked well enough on the Spridget engines and didn't wear unduly as far as I know.

I'll also go into my loft and measure the shaft on my 1275 g/box.
Lawrence Slater

O/D for the bronze in a 1275 Spridget engine, is 5/8". Found it on the internet.
Lawrence Slater

Lawrence,

I suspect the Marina used a needle roller spigot as it also used a roller release bearing. Both more durable than the carbon thrust and oilite of the earlier offering.
David Billington

I see you've already got the measurement of the shaft on your own g/box.

Anyway, I can confirm that the crankshaft hole is 5/8" on a Spridget engine. So compare that to the Marina.

Others have used a Marina engine and not mentioned problems with the standard spigot mating to a ribcase as far as I know.

As for removal. 3 methods.
1) You can get a puller.

2) You can pack the bush full with grease, and if you have a snug fitting drift, ram it in, and the force will expel the bush.

3) Since you want to replace the bush anyway, do what I've always done. Hammer a drift onto the edge of the bush. This will distort it(destroy it), and you can hook it out. This doesn't harm the crank at all, as the bush is very soft anyway.

Edit. Ah thanks David. Didn't know that.
Lawrence Slater

Earlpart sell roller bearings that are said to fit marina and 1275 Spridgets on ebay.

http://www.ebay.co.uk/itm/MORRIS-MARINA-CRANKSHAFT-SPIGOT-BEARING-/300580000080
Lawrence Slater

Anyone got an A series gearbox input shaft they can measure the diameter of the spigot on. Tim mentioned his is 12mm but I thought they were 1/2" (12.7mm) but not sure and I don't have one.
David Billington

Have just measured a shaft and found it to be .497" dia. so would assume the bush/bearing would be .500" hope this helps
c c carpenter

lawrence. Those ebay bushes do not fit a 1275 spridget crank. Believe me I've tried.
In fact, if anyone wants a brand new and unused marina roller bearing spigot bush they can have it for the cost of postage ;-)
graeme jackson

Hi Guys,
Thanks for the sudden flutter of activity!
have been out and measured it all again.
The OD spigot (measured from two gearboxes) on the gearbox is 12.6 (near as damn it 0.5 inch)
The inner diameter of the spigot bearing on my marina engine is between 12.7 and 13 mm
the outer diameter of the spigot bearing (roller) is 19 mm (0.75 inch).
This seems to match the OD of the bronze spigot bush in the end of crank (assessed by placing the replacement roller bearing behind the bronze bush in situ and eyballing it..
So looks like the dimensions are OK. The in situ bronze bush is probably a little worn so should be replaced.
I'll get a replacement bronze bush from AH spares and then make a decision on which solution to use?
Cheers
Tim
T Dafforn

Tim,

Looks like drawn cup needle roller bearings are available that'll fit such as http://simplybearings.co.uk/shop/p92879/BHA88ZOH+Needle+Roller+Bearing+1/2x3/4x1/2+inch/product_info.html , although you would really want one with a seal to face the gearbox end. Maybe Graeme can measure his surplus Marina roller bearing and confirm whether the OD is 3/4" (19.05mm).

That link needs to be cut and pasted BTW.
David Billington

david. sorry for taking so long. Finally found the ebay bush at the weekend and it's just over 19mm OD - Can't be any more precise as i don't have a gauge THAT accurate :-)
graeme jackson

This thread was discussed between 21/05/2013 and 28/05/2013

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