push rods

[zefarelly]

right . . . here I go again

push rods . . . . does anyone make them ???

I have a set of forged cosworth pistons with a lower crown height (3-4mm) and I'll be skimming the block accordingly (almost definitely I think) along with the big valves I'm using which are slightly longer also I think I'm going to need shorter push rods, or parhaps even taller rocker shaft posts . . . .has anyone ever dabbled ? ? ? or got any suggestions (not give up and get a proper engine!)

[avsfan733]

lots of people will make you pushrods with whichever tips you need to whatever size...only one i can think of off the top of my head is paeco who do them in steel and in titanium if your heart so desires...btw remember it will change your timing probably because of the change in length of the timing chain

[KC]

The Chevy we race uses the physically largest valves we can get into the bore, they literally reach across the bore and nearly touch each other in the middle. We run 2.25 (57mm) intakes and 2.187 (55.5mm) exhaust valves made from stainless steel by Manley. But, going to bigger valves, as you mentioned, is only part of the equation. Bigger valves require more valve spring tension to overcome their mass. More valve spring tension requires better mounting hardware to overcome the tension from the valve springs and inertia of the valves and valvetrain.

We use ARP heavy duty and extra long valve studs in the head made especially for our roller cam setup. The studs are extra long to accomodate a stud girdle, which bridges every valve stud and ties them all together and strengthens the upper end. We run dual valve springs that generate about 500 pounds of valve spring pressure to keep the rollers on the cam and not floating. The push rods are oversize 11/32" diameter (8.73mm) with commensurate oil galley for the upper end. All use a hardened ball seat where they sit in the roller assembly and in the rocker arms to reduce friction. We also run titanium spring retainers and shim index each set of springs to prevent uneven spring tension loading on the cam. The push rods we run are Manley units but Competition Cams, Lunati, and Iskendarian offer similar and worthy push rods as well. Just about all of them take custom orders as well. There are many more puishrod makers out there, but I am not sure how available any of them are across the pond.

You will need to study the valve geometry for your application before ordering unless you are merely replacing existing units. Comp Cams offers a multitude of variations...

The have ordering and geometry information here...http://www.compcams.com/information/Products/Pushrods/

This picture is one of our race engine with the valve covers removed. The red anodized part is the stud girdle that clamps all the valve studs together.

[KC]

BTW, what engine are you running. You mentioned Cosworth pistons, Ford power or aftermarket parts for some other engine?

[Red Dog]

Zefarelli,

The easy and cheap fix is to shim the rocker pedestals. Use some ally sheet and cut them out with a drill and a file. Don't forget the oil hole! Limiting factor is rocker cover clearance.

BTW the height of the centre of the rocker shaft/top of valve relationship must be optimised to get the full valve opening. Best found by experimentation. If you go the route of having special pushrods made you must do the set up first or you will have wasted your cash!

[zefarelly]

its just a 4 Cylinder pre cross flow ford engine, 1500cc. bore 81mm, stroke 72.75mm, as I've elected to go FiA spec I cant use all the proprietry tuning stuff regardless of its cost as most of it is non historic, and therefore illegal, loosing 2mm off the block to offset the piston crown height, shouldn't affect the timing chain as it has a tensioner and its tight enough to fit anyway, the valve head Dia isnt the issue, but the stem length is . . . . .no valve clearance as theyre a fewmm longer . . . .taller rocker shaft blocks, but they only come +0.050" . . . .Can I safely make +0.100" or will that affect other things . . . . either way, the push rods will need to come down at least as much as the block if I do that . . . .I think longer conrods would offsett this as well . . . .but that expensive !

[KC]

Can you just replace the valves with shorter ones? Shimming the rocker arm studs would be easy to do as well and probably least expensive.

[graham bahr]

longer valves are a bad idea as it will ruin the rocker geometry, and necitate even more shimming of the posts (assuming you already have the extended length ones)
with new adjuster screws which will be tighter in the rockers i would of thought you could of made up the difference in the pushrod length required.

instead of skimming the block to hell, have you considered using a longer conrod? are x/f rods longer? a longer rod will usually develop more power as the piston will dwell at TDC longer which is good news in most 2 valve engines which all suffer from insufficent cylinder filling, and is better for the bores as it reduces the rod angle and thus side thrust on the piston skirt/ bore.

[zefarelly]

spot on Graham . . .exactly what I was reading about last night . . .except shoestring finance doesnt stretch to buying new rods (£700) at the moment . . .and Ive just found a set of pistons which alleviate all the problems . . .so I think I'll sell the Cosworth ones and buy the alternatives instead, same forging just slightly over bore, a whisker higher crown but otherwise exactly the same, I just need to search for the best deal . . . .anyone knoe any MGB race engine bit suppliers ?!

[graham bahr]

mgb race engines, don't they use twincam pistons? ivor searles bore lots of mg engines they might know something, ring 01353 720531, option 3 and speak to trevor

[graham bahr]

or ebay!

[graham bahr]

this is probably illegal, but another option might be to ofset grind a 1600 x/flow crank to shorten its stroke, if you go .040 undersize and offset it by the same amount the stroke would be 75mm or to put it anotherway, 2.5mm longer than you've got now, that would save you having to skim the block at all. that would give 1545cc on a std 81mm bore.

and before some one says grinding a crank that far weakens it too much,
consider this the standard crank pin is 1.9370 inch so, do you really think that removing 0.040 or 2% of the pin is going to make any difference when no one doubts the strength of a crank ground 0.020, when they stroke "A" series cranks they grind them down by 0.25

[zefarelly]

hmm . . .twin cam pistons in MGB's . . .that makes sense . . . I'll call him for a chat, as I want less bore than Twin cam that makes my idea feasible.

std Crank is fine, If money was no object I'd buy a new ally block, and longer rods for the cosworth pistons, then 10k RPM here we come !

I've also just found some original Stailes group 1 valves too

[bartman71]

Originally posted by avsfan733
btw remember it will change your timing probably because of the change in length of the timing chain

it wont change the length of the timing chain as it is not O.H.C
decking the block won't alter the length between the crank and cam

[avsfan733]

good point bartman your right

[zefarelly]

MGB oversized pistons are nearly identical to GT Ford pistons . . . .but easily accessible.

problem solved ! along with having found original Group one valves, a set cosworth rods and a farndon crank . . .we should have an 8500 rpm screamer with standard pushrods and for less than 3 grand for the whole engine

Del boy dealing strikes again !

[graham bahr]

i love it when a plan comes together.......

[zefarelly]

so do I . . .thanks for all your suggestions . . . .sensible on the whole I might add too !