Best pushrods for a 1960 99

The narrow originals. The fatter ones might just scrape on the pushrod tunnel or, more likely (as I know all too well), if the head gasket protrudes at all into the pushrod tunnel - as they can - it will saw into the fat pushrods the moment you start the bike. Having said that, you can use the fatter ones successfully but you have to be rather careful about clearances. The later barrels have a bit more room in the pushrod tunnels so it's less of a problem with them. Gordon.

My '61 99SS has 'SS' stamped into the top of the barrels. The SS had very few engine dfferences from the standard, so most probably the only difference which required the SS barrels to be distinguished was the wider pushrod tunnels. Mine does have the fatter rods.

Maybe the attached pic shows obviously fatter tunnels than yours.

Steve

Neil

Thinking about it, what I told you was probably misleading, I seem to remember that the 99SS was given the same barrels as the 650SS, but must have been machined down on the barrel/crankcase flange to suit the shorter stroke - 3.5mm. The deeper spigot thus would have protruded further into the crankcase and would have cause a clash with the conrod. Consequently recesses would have been needed to be ground out to clear the conrod for-and-aft, as can be seen on my pic, at the bottom of the barrels. It was done unbelievably crudely, looks like it was done by a chimp with an angle grinder. Can anybody confirm or deny the presence (or absence) of these recesses on the 650SS barrels?

New rings can knock against the ridge at the top!!.

Previously steve_marshall wrote:

Neil

Thinking about it, what I told you was probably misleading, I seem to remember that the 99SS was given the same barrels as the 650SS, but must have been machined down on the barrel/crankcase flange to suit the shorter stroke - 3.5mm. The deeper spigot thus would have protruded further into the crankcase and would have cause a clash with the conrod. Consequently recesses would have been needed to be ground out to clear the conrod for-and-aft, as can be seen on my pic, at the bottom of the barrels. It was done unbelievably crudely, looks like it was done by a chimp with an angle grinder. Can anybody confirm or deny the presence (or absence) of these recesses on the 650SS barrels?

I had new liners fitted to my 650 SS barrels some time ago and I had to file the slots you mention in the base of the barrels to clear the rods. This involved the fitting and removal of the barrels a number of times. Some time after this I came across an old friend who had obtained the correct dimensions from somewhere.

The 650 and 99SS are supposed to have used the same barrels. But over time and the odd rebuildthis may not be so on any one particular machine. As Gordon says the 650 pushrod tunnels are a little wider to suit the fatter SS pushrods. To help identify proper 650/99SS barrels look for two other more obvious differences.

650 barrels have a lot more finning at the front between the exhaust port areas. Also the casting number can be found at the back of the bottom flange. Checkout the attachment. The extra finning is very clear.

A fewother important points worth a mention. The 650 crankshaft had 1.75" journals. The 99SS used a 1.50" journal.

The 650 con rods are shorter than the 99SS rods.This helps to keep the compression ratios similar despite the bigger 650 crankshaft stroke.

The bore of the 650 and 99SS are the same at 68mm but the 650 pistons have cutaways to clear the crankshaft journals. Also the 650 barrels have slots/recesses to give clearance for greater throw of their rods.

650 and 99SS barrels were the same length from top to bottom except for the first batch of Manxman 650 barrels which had aslightly longer bottom skirt. This all changed when the 650 barrelslost their topspigot in 1965.

The 650 and 99SS are supposed to have used the same barrels. But over time and the odd rebuildthis may not be so on any one particular machine. As Gordon says the 650 pushrod tunnels are a little wider to suit the fatter SS pushrods. To help identify proper 650/99SS barrels look for two other more obvious differences.

650 barrels have a lot more finning at the front between the exhaust port areas. Also the casting number can be found at the back of the bottom flange. Checkout the attachment. The extra finning is very clear.

A fewother important points worth a mention. The 650 crankshaft had 1.75" journals. The 99SS used a 1.50" journal.

The 650 con rods are shorter than the 99SS rods.This helps to keep the compression ratios similar despite the bigger 650 crankshaft stroke.

The bore of the 650 and 99SS are the same at 68mm but the 650 pistons have cutaways to clear the crankshaft journals. Also the 650 barrels have slots/recesses to give clearance for greater throw of their rods.

650 and 99SS barrels were the same length from top to bottom except for the first batch of Manxman 650 barrels which had aslightly longer bottom skirt. This all changed when the 650 barrelslost their topspigot in 1965.

hello the cutways on 650 pistons are round the boss area they a shorter skirt to the 99SS on the boss sides , I think at some time in the past some one has changed barrels to the early standard 99 slimline model as they still had the thin type push rods, but the barrel look nearly the same,as the 99SS, so you then have narrow push rod tunnels , so I think this is were this problem lies , yours anna j

The 99SS barrels are like the 650SS in Phil's photos, with deep fins in fron of the pushrod tunnels, except the reliefs for the conrods at the bottom are done very crudely. Shorter 650SS rods would mean that the barrels could be identical.

Steve