I am midway into rebuilding the top end of my 1956 Dominator 99 and on checking the push rods I have found that one of the exhaust push rods is badly bent and the other three are scored. They are tubular aluminium with steel ends.
Can anybody please advise me what the correct overall length of the exhaust and inlet push rods are for the 99 and a recommended suppler of new ones.
I assume that the camshaft is standard although I have no history of it's previous rebuild. I have done approximately 400 miles on the bike since purchase earlier this year.
Its common for the pushrods to get misplaced and trapped , but that could also indicate a careless PO . So I would carefully check everything .Might be a good idea to check that a valve is not coil bound too.Might need to check the type of cam fitted as this may need rod type to match.
Thanks for the information Philip. I will contact the usual suppliers next week.
As a matter of interest what is the best way to determine what crank is in the bike ? Is it just a matter of checking the lift particularly in relation to the pushrod lengths ? I am not sure of the comparison.
Further to my previous comment and after further deliberations , considering that I am going to fit a compression plate to the underside of the barrel and that a p/o had skimmed the top of the barrel and in addition the cylinder head has had a light skim , I have convinced myself that I need to determine the correct pushrod lengths before contacting possible suppliers . What is the preferred way to determine the correct push rod lengths ? George
If it were me, I'd straighten the bent rod and assemble with what I had, and check the valve contact geometry to work out if they need to be longer or shorter. It won't take all that long, as you only need to snug up the four main cylinder head bolts, and you won't be fitting the carb and pipes. Also you might find out if the scoring was the result of them being too fat for the pushrod holes in your engine, or the results of them previously becoming dislodged from their cups during an assembly error.
The fat alloy pushrods arrived with the 650 engine in 1961. As I understand it they might not fit the earlier engines - no doubt Phil will know!
How bad is the 'scoring'? They are not like con rods where very high tension stresses from inertia effects might cause scratches to become cracks.
Thanks David. I will see about doing as you suggest but I will have to get new push rods as they are a mixed bag of alloy and steel. Although all this is a new experience for me I am sure that the pushrods are not of the fat type variety.
As an addition I might make an adjustable pushrod which perhaps will be easier to finalise the lengths.
Would the larger diameter pushrods be ok for my 1956 Dominator 99 ? George
As already mentioned , the barrel shaped p/rods appeared in 1961 and it's likely that if you were to try and fit them they would foul up in the pushrod tunnel, but obviously you would check before final assembly.
Hi George.......The fatter pushrods arrived with the 650, 500SS and 600SS engines. Roughly late 1960 onwards. The barrels had slightly enlarged tunnels to cope with the increased rod widths. So any pre-1960 barrels will struggle to cope with the fatter rods unless some machining has been done.
When engine producing moved to Plumstead, some of the machining of both barrels and cylinder heads was so was poor that, even in the later engines, the pushrods rubbed on the tunnel mouths, or against the gasket edge or against each other.
You must be very careful when changing the pushrod lengths in order to avoid the rockers ending up thumping the roof of the head or running out of adjustment.
I have now fired up the engine a couple of times and there are no worrying noises. At least so far ! I am waiting for the weather to improve to start the running in process. I must say that I was not aware that there could have been a potential contact between the rockers and the cylinder head. Another point on my learning curve.