Hi All,

After many enjoyable years smugly reading about the misfortune of others on this forum it has now happened to me.

Last week the Mrs was out in our newly acquired 1969 500L and managed to strip the splines on one of the driveshafts. Once I had finished making her feel thoroughly guilty for her obvious abuse of a classic piece of motoring history I ordered some new parts and got to it. No worries thought the brave man. Just pull the thing apart, fling some new bits at it and all will be sunshine and happiness again.

Then I thought that while the motor was out I would have a look at the thermostat flap the previous owner had welded in a fixed position and sort some of those annoying oil leaks. So I cleaned the outside of the motor, pulled the cowls off and cleaned it again. Then off came the sump. From the bottom the pistons looked new (I had been told the engine had been freshly rebuilt) the cam looked not too bad and all seemed in order. You could even still see the honing marks. Then I noticed the scuff marks on the #2 piston with matching marks on the bore. I was suspect of the quality of the rebuild anyway as many of the bolts on the outside were non standard and loose. At least one was held in with silicone!

Don't you find swearing helps in times of stress?

Questions for those that know.....
What is involved in fitting a 650cc kit?
Is the performance improvement worth it?
I have 650cc barrels, just need some pistons.... can I use the 500cc head?
I am guessing I will need a 650cc head gasket?
Is it worth upping the compression ratio?
Do I need to fiddle with the carb?

Many thank you's in advance
Chris

looigi said:

Hi All,

What is involved in fitting a 650cc kit?
Is the performance improvement worth it?
I have 650cc barrels, just need some pistons.... can I use the 500cc head?
I am guessing I will need a 650cc head gasket?
Is it worth upping the compression ratio?
Do I need to fiddle with the carb?

Chris

Click to expand...

Hi Chris
So you are thinking of going over to the dark side
The biggest you can do on the standard crankcase is to go for the Nanni 540 kit. A modest increase in capacity but also includes the high compression Pistons. If you go for 594 or 652 conversions on the standard 500 crankcase and I have done both then you need to have the crankcase bored to suit the barrels plus a spacer under the barrels to compensate for the shorter barrels from the later engines. Head will fit ok with larger gasket and you may smooth out some edges to avoid hot spots. Proof of the pudding is in the eating but don't microwave it

Using the original case is do-able, not ideal. The boring of the case reduces what metal area is left and the stress of use over time can cause the case to crack. Not optimal which is why many start with a 126 case to start modding.

The advantage for some when boring out the crankcase is simply that you get more power with the engine you have. For others they want the power along with retaining the external appearance of a standard 500 engine etc. The 594 engine I built on a 500 crankcase had a small skim on the lower skirt of the barrels and a small skim on the crankcase with spacer rings. Spacer rings add no strength to the crankcase but the brief for this engine was just a little more oomph for getting up the hills and with the minor machining no major loss of strength. The 652 engine was a straight crankcase bore on an engine with some tuning I guess to about 30bhp but then the mod backed up by the 10mm dural spacer plate under the barrels. Engine seemed solid as a rock.