Can we talk about crankshafts?

[Fux]

I have a TS1 build on the shelf.

Standard barrel and piston, LTH manifold with a TMX 30 and MB Clubman.

The crank that was originaly in the engine apperars to be a standard Injun GP job and feels very sloppy at the big end compared to the Afla in my RB.

I`m thinking about going with a 60x115 from MB but i`m not sure about piston clearence @ BDC. Whats the normal thing to do ?

Is it possible to machine the piston down, say 1.5mm and use a 7.5mm packing thus effectivly lowering the ports by 0.5mm for slightly more low down power or is there something else I have to take in consideration when it comes to skirt length?

[Fux]

Hmm.. hang on, thinking about that, being that the MB crank has a 115 rod It should be way of hitting the case @ BDC but the question still applies somewhat because the barrel will be further out of the mouth because of the packing plate.

I need some edjucation on the subject.

[soullad]

Why do you want to alter the stroke and rod length of your crank? You have a standard kit and piston, why not fit a standard 58 x 107 black mec eur race crank and assemble as is?

[Fux]

Why do you want to alter the stroke and rod length of your crank? You have a standard kit and piston, why not fit a standard 58 x 107 black mec eur race crank and assemble as is?

Because i can?

In my experience a longer rod cuts some vibration. I`ve had problems with cranks in the past and just want the best parts I can get hold of for this rally going cruiser.

Doing it simple, I could go for a 58x115 and use a 8mm packer, but i would stil like to lower my port timing half a mil, as Iv`e also had some succsess with that in the past.

[corrado]

I thought that the main reason for 115/116 rods being smoother, ie less vibration, was the positioning of the gudgeon pin higher up in the piston. Surely you'd negate that benefit using a TV rod and packer. MB should have an a Racetour option for TV rodded piston.

[warts]

I don't think the deck height (gudgeon pin centre to piston crown has any bearing on the improvement of vibration levels or not. That is purely down to the rod/stroke ratio. A graphical plot will show this readily. My intuition on the long ring group is that shorter is better, it has less flop over the dead centres to be controlled, giving the rings a slightly easier time.
The trend in racing stock based v8's stateside is the most compact ring group possible. Lowest deck height reduces the volume of trapped end gas round the ring group, helping reduce any liability to detonation.
I did have a paper from General Motors/Smokey Yannick who originally (maybe) started this r/s ration thing off back in the late 50's, early sixties, trying to improve durability with V8's for NASCAR stock car racing, when they were much more stock than now.
Smokey figured that with the longer rod, the piston dwells around the TDC longer, giving more time for the burn, which is important in a whopping great combustion chamber. I think for racing the vibration reduction was a welcome side effect.
Although this is all came from a 4t background, I don't see any major reasons why the same principles should not apply to a 2t. Ports and windows permitting.

[corrado]

MB should have an a Racetour option for TV rodded piston.

http://www.lambrettaspares.com/search/7000PR32.html

[Darrell Taylor]

going 60mm stroke will inrease the port durations when used with a base packer as most cranks are normally supplied ,why i dont know as its the last thing you would want to do when using packers alone as it carries 3 negatives an increase in ex duration,an even bigger increase in transfer duration due to transfers sat lower in the cranks rotation,which results in a lower blowdown figure
if you alternatively use a head rebate achieved by cutting the head or using a thicker head gasket/packer you can use the space created by the longer rod and stroke to lower the cylinder which will lower the ex duration ,lower the transfers even more which in turn will increase the blow down figure producing a better performance all round , its the extra blowdown thats the winner here as ts1 transfers arent too high a number its just the ex hasnt enough lead on it to evacuate the ex gas before the transfers open
the clubman will be best on a 107 or 110 rod as hasnt the same extraction effect as an expansion so relies more on old school small case volume but for achieving the better blowdown the 110 be best so youll have 1mm for the extra stroke (1 up 1 down) and 3mm on rod total 4mm of which you can run say 1mm base and 3mm rebate/packer to achieve the maximum cyl lowering effect (no cutting required on piston as the longer rod sits the piston 3mm higher and clears the case

[shamrockexpress]

so going by what you have said aboveis their much more gain over a 58mm and 107mm rod.
If a TS1 was designed around the standard configuration is this not best especially for touring.
I,m only asking as i dont know!
thanx

[Darrell Taylor]

theres no substitute for cubic capacity when going for grunt and low down pull when a motor is off pipe so when ur spending on a crank the cost is around the same so would go the 60mm route over the 58 every time ,the longer rods give u the flexibility to put the cylinder where u want it via packers for bottom/mid or top end emphasis and used in conjunction with porting makes for set ups to suit the pipe that is chosen
the ts1 casting although designed for 58 i find is configured better to the 60mm stroke

the chaanges i suggested would move the emphasis of the ts1 as a sports cylinder to that of a touring cylinder