51 G9 oiling modification/upgrade?

wilko · Post by **wilko** » Sun Jan 16, 2011 9:55 pm

I have a spare wide timing cover but as usual it would cost a fortune to post to you from here in Oz!

chasdev · Post by **chasdev** » Sun Jan 16, 2011 10:35 pm

I've got two covers from 1956 engines, but they look to be the same as the 1951 as they lay on the bench.
The change will be from the tiny 51 pump to the larger 56 so the cover should work out, but thanks for the offer.
Now if I could just find a set of undamaged barrels..

Eric · Post by **Eric** » Sun Jan 16, 2011 11:16 pm

Unless there is a secret I don't know about the pumps were not changed in 1956 but much later around 1962 I thought. That's when the timing cover with bumps was introduced. There was a change in 1952 according to Bacons book, but I don't know the details.

Groily · Post by **Groily** » Sun Jan 16, 2011 11:44 pm

Pretty sure all your timing covers will indeed be the same Chas, for the reasons Eric gives. The change was a later 650-driven thing. A fat return pump won't go under any of the early covers.
Reckon the size of all your pumps will originally have been the same (ie small), though someone might have swapped bits already. I don't know about the '52 changes either.
Probably find that Steve Surbey at AMC Classic Spares has resleeveable - or even straight reboreable - cylinders available, he usually does.

chasdev · Post by **chasdev** » Mon Jan 17, 2011 12:00 am

The first twins pumps used one "normal" (as in same as 56) gear set and one smaller gear set..
I've read but now forgotten when they went to both the same size..

Eric · Post by **Eric** » Mon Jan 17, 2011 12:00 am

I don't think they were ever the same size, as the return pump was always made bigger than the feed, to ensure it would always scavenge completely.

It often has to start with quite a lot of oil to move if the bike has been left and wet sumped

wilko · Post by **wilko** » Mon Jan 17, 2011 1:17 am

They were all the same until the "60's. The early mod probably had to do with the new type pressure relief valve requiring an alteration to the timing cover to allow for the new plunger type on the end of the filter chamber.

Groily · Post by **Groily** » Mon Jan 17, 2011 5:44 pm

Yup. When I said 'small' I meant small pair as opposed to big pair, as the two pumps of any pair are never the same. There are 4 pump sizes AFAIK, small in and out, and big in and out from '62-ish. Out is always bigger than In, on these as on any dry sump engine.