Crank Balancing DIY

[JulianS]

For the very brave there is this rather brutal technique from a 1959 bulletin from Hap Alzina in California.

[Seabee]

Wow Julian, we Yanks are some crude creatures sometimes! Sadly though , it completely made sense to me!

[RDfella]

When the engine is apart, drill holes to make the crank over-balanced by a couple or so ounces. Then drill the opposite side until it is underbalanced by a similar amount. Tap that second batch of holes. You've then got a range of balance factors you can apply simply by fitting / removing screwed plugs from those latter holes. When you're working with experimental engines, where the balance factor is at best a guess, it's by far the easiest means of achieving a smooth engine. Been doing that for ages, though I think Richard too exception to the method when I mentioned it a while back. Maybe he misunderstood the expression 'window' that I used to describe access to those plugs. Of course, in most cases that 'window' already exists above the sump plate.

[Seabee]

Well, I couldn't just let it be. I decided that by adding a few more drillings, I could lower the amount of weight I had to add to balance the crank. I did 3 more drillings and got the rotating weight down to 1190. With my recip weight, I settled on 58.33%. I think that will work pretty well for my style.

[Seabee]

G'day Seabee.
I'm flattered.
The only problem with using an A7 head is the valve size. I ended up with a bit of a mish mash. SR valves but had to marry the A7SS collars to the SR collets and use SS springs. Using the SR gear the springs will bind, especially with a 357 cam.
Cheers

Howdy Musky,

I have completely restored the A7 (SS?) head with stock valves springs and keepers. What do I need to do to make it work with the 357 cam? I have a lot of time and $ invested in the head and really want to run the 357 cam. Is there a solution I can pursue?

Thanks in advance,

Seabee

[JulianS]

I have not used the A7SS head, however I used a 357 cam with an A10 iron head with standard A10 valves etc for many years and had no issues.

Currently using a 357 with A10 iron head, Road Rocket valves (not the big inlets), Road/Super Rocket spring seats and collets and Eddie Dow type top collars (from Ebor motorcycles) with WS type progressive springs. That works fine also. Why Road Rocket valves you may ask? Because I had a good set plus the bits to go with them from a wrecked (big crack) 67 1549 alloy head.

I assemble with a set of very weak springs first to makes sure of top collar to guide clearance and with proper springs check they are not coil bound.

[muskrat]

G'day Seabee.
The 357 will be fine with an SS head and valve gear. I wanted the bigger SR valves in the Cafe's twin port SS head which is where I had to do some creative fitting.
Even my 51 A7 plunger has a 357 (with a 57 SS top end).
Cheers

[Seabee]

Thanks Julian and Musky! What a relief..................

[Rocket Racer]

A useful reference article from a book on A65 development

[rocker21]

had a lot of trouble with my A7ss and a 357 cam, it broke a pushrod, turns out the standard valve spring setup gets coil bound on full lift, had to get some machining done on the spring base and on the valves to get clearance, seems i am not the only one to have had this problem.
 

[RDfella]

There's a lot more to fitting a performance cam than many realise. Apart from matters such as inlet and exhaust pipe design, there's valve gear acceleration, valve gear clearances, valve spring and cotter / collar to valve guide clearance, valve to piston clearance and even valve to valve clearance to take account of. Ain't just a bung-in and whizz off in a cloud of tyre smoke ..........

[muskrat]

There's a lot more to fitting a performance cam than many realise. Apart from matters such as inlet and exhaust pipe design, there's valve gear acceleration, valve gear clearances, valve spring and cotter / collar to valve guide clearance, valve to piston clearance and even valve to valve clearance to take account of. Ain't just a bung-in and whizz off in a cloud of tyre smoke ..........

G'day RD.
Hit the nail on the head there.
Even more work to fit SR valves in A7SS twin port head! Everything has to work in unison.
Cheers

[Rocket Racer]

had a lot of trouble with my A7ss and a 357 cam, it broke a pushrod, turns out the standard valve spring setup gets coil bound on full lift, had to get some machining done on the spring base and on the valves to get clearance, seems i am not the only one to have had this problem.
 

Also worth considering use case. the 357 is a great cam and works really well above 5000, but the 356 is no slouch and very strong to the low 6's and better mid range than the 357. Don't get me wrong, I've seen my sidecar light up out of corners to 7500 on the 357 but on a road engine would choose the softer 356 for the mid range between 3-5k. The extra couple of ponies claimed were at revs the average preunit twin owner will never dare use. Appreciate we do have some here who do use ALL the throttle available and for them the 357 delivers a wee bit more up the very top. The 7500 I've seen is not the engines limit either, it needs watching up there as I think it would happily go higher, I just expect it would go bang. Musky will no doubt know but expect 8k with a 357 in a 500 is on the cards. I have broken engine mounts off the cases, cracked frames and head steadies due to balance issues, but then I've also broken hubs

[rocker21]

many moons ago i built an A10 that was very modified, needle roller bearing everywhere, 9:1 pistons, large valve alloy head that was ported, using a gardener carb, it had a polydyne cam which is very like a 358 cam, it was all balanced and went like the clappers, it was a bit of an animal on the road, good fun though, it was loud , never had any problem with the springs getting coil bound, but it did have goldstar springs in it. it revved well,
had to fit an electronic rev counter as it kept braking the normal smiths one. a lot of fun but not really suitable for todays roads.

[KeithJ]

Interesting read as I am looking at balancing my SR crank.  Not having any "knife edges" I am considering mounting the crank between live/rotating centres on my lathe.  Has anyone tried this?  Just concerned about the amount of resistance in the bearings in the centres.  I've tried two centres and the difference in how free they run is considerable.