Looking for some info and advice regarding pushrods for my 'mix and match' 1959 Dominator 99.
I've been running this in (gently?) for just over 1000 miles after replacing both the head and barrels last winter (the 'new' head is a refurbed early-1960 model 99 casting 22707 with some reasonable porting work done by one of its previous owners).
During the rebuild, I (foolishly?) stuck with the fat barrel-shaped alloy pushrods that had been no trouble in the previous incarnation of my own engine (using an early-1959 T2225 head).
On inspecting the top end one year on, I am now faced with some badly scarred rods and a few minor wear marks inside the tunnels of the new head - as shown in the photos. All four rods had at least a few bruises, and the worst one had a 1" long, 0.7mm deep scar. None of the rods was bent though, and I'm wondering if any of them can be salvaged: I've currently asked my brother to turn them all down just to the point where the scarring is gone, and have naturally ended up with four different shaft diameters of 7.6, 8.6, 8.7 and 9.4mm (the original fat-barrel diameters were all around 9.5mm - i.e. 3/8"). The rod weights (including end caps) are now 33, 38, 42 and 44g (exhausts and inlets in turn). My rationale for only going this far is that these are the fattest rods that might fit this combination of head and barrels without further scarring. But I am unsure whether to risk using the rods again, and am therefore looking for advice:
(1) will the turning process have weakened the rods in itself? I am presuming that the originals would have been made from rolled bar, but don't know/understand what difference this will make.
(2) will using 'unbalanced' rods lead to any marked problems? I could easily skim the fattest of each pair of rods down further to match their respective partners, but this will obviously weaken them further, and I'm not sure if there's a good trade-off to be had.
(3) does anyone know what diameter the 'thin' rods that were originally fitted to the 59/60 model 99s were? After searching for web-images (and looking at the NOC-shop's part number M14/82) I'm guessing that some might have been as 'thin' as 1/4", with modern after-parts maybe being around 7mm diameter. But it would be great to know what they were supposed to be originally (and/or what problems this caused, for normal road going machines).
Hoping to be enlightened, and happy to be criticised...
Nigel C
99 pushrods
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Thank you Philip
That's quite encouraging, and certainly useful information, thank you Philip. After a little reflection, maybe I've been overthinking the need to match diameters/weights, and potential weaknesses. But I'll hang around a while for more comments before refitting, just in case there's an error in my way... :)
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The push-rods that you were…
The push-rods that you were using and have damaged are for the 99SS and 650SS varieties of the Dominator and were also used in the Atlas and Commando engines. They are made in hollow-blown process which keeps down the weight but makes them stronger. The push-rod tubes in the casting of the barrels is wider to stop the push-rods rubbing - as you have found, sadly. Your engine will be quite content with the set of push-rods that Phillip has depicted. Good luck, Howard
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These are the type of pushrods that should be inside your 99 barrel. The attached photographs may also be of use. The rod diameter is generally 1/4" for the 88 / 99 versions. The length measurements are rounded up / down.