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[ChrisD]

Adrian. I too went the steel conrod route and roller bigend for my 535cc. You must get it balanced as only a small amount out-of-balance means LOTS of destructive vibration.

When new I measured the balance factor on my 1996 bike (now 535cc) it was about 68%. When I fitted the steel conrod, I found the OEM conrod was ~20 thou longer than expected, perhaps due to stretch! I followed some advice (NOT our hosts) and didn’t re-balance the new conrod. The destructive vibrations caused by the balance factor being out by ~45grammes, cost me the drive side crank pin, stator and other stuff. When we then balanced the crank, I followed the reported advice by Fritz Egli (British Bike Magazine, Oct 1994) and set the balance factor to 61-62%. That is definitely smoother up to ~3500rpm but doesn’t damp enough vibration at higher revs making acceleration through the gears quite unpleasant. I now have to replace the piston because of a dropped valve when the aluminium valve retainer snapped. This was caused, we think, by the OEM tappet adjuster being offset to the pushrod by a few degrees which resulted in the pushrod flexing continually leading to valve bounce. I shall set the balance factor now to 63% and advice on results.

Cheers, ChrisD

[Bullet Whisperer]

I have never changed the balance factor when swapping from alloy to forged steel conrods and have never had a problem with vibration as a result, likewise with swapping pistons. Also, when I lighten my crank assemblies by a few pounds at least, I restore their original balance factor, then fit whatever conrod, piston etc which goes into that particular build. Before I get condemmed for this, I once perched a cup of tea on the seat of the 350 racer [when it was still 90mm stroke with one of my modified Redditch cranks inside] and revved it to over 7000 rpm and it rippled quite a bit, but stayed there. TRUING the crank is of far more importance to me, than balancing, although obviously this matters, too, but to a lesser degree for me at least.

[Tomshayes1]

Hi guys.. Wow thanks for all the responces... The bikes only done 3500 miles.. Bottom end seems ok.. Carb is 32 mm..

Tom

[Tomshayes]

Assuming that I go for the steel rod upgrade.. What's the feeling on the necessity of going for the roller bearing.. I wont be racing but just having the occasional blast for fun.. Obviously the cheaper option would suit me better ha ha

[Bullet Whisperer]

Hi Tom, you could just fit the British made alloy conrod and a plain big end and it would be a big step in the right direction, I have fitted at least a couple of these for owners over the years. Regards, Paul.

[Tomshayes]

Ahh Cheers Paul.

Would a compression plate help?.. I am also upgrading oil pumps

Thanks

Tom

[Bullet Whisperer]

Hi Tom, if I wanted to build a good all round engine for a reasonable price, I would fit the British conrod, plain big end, decent mains, alloy barrel, American so-called 9:1 piston, port the head and use the standard cams, with the inlet retarded by 1 tooth. The standard oil pumps are up to it, if in good shape, the high capacity ones are a better option if a roller big end is fitted - there will be less strain on the oil pump drive train and more lubrication and cooling from the extra oil being flung around inside the flywheels. Regards, Paul.

[Bullet Whisperer]

I wouldn't fit a compression plate, by the way.

[Tomshayes]

Thanks Paul.