All the exhaust mounting studs are 8mm x 1.25mm. If the engine is in the car, I would suggest that you make your own studs---use a finishing tap to gain a couple more threads in the BOTTOM 2 stud threads that hold the silencer clamps in place, then make studs that utilise that extra depth of thread. Leave enough clean 'shank' to allow for the thickness of the clamps and then enough 'top thread' to allow for a flat washer and a couple of PLAIN nuts---1 nut to tighten up on the brackets and the 2nd nut to 'lock' the 1st nut. I NEVER reccomend using any sort of 'locking' nut. The top 2 studs pose a bit more of a problem because the threads go all the way through the crankcase, so try and use a stud with just a couple more threads then the standard studs. Don't use a tap on the top stud threads in case any swarf drops into the sump. If the engine is out ( or the sump off) then the (ex factory Abarth) trick is to run a tap ALL THE WAY THROUGH THE TOP STUD THREADS and fit a screw (again 8mm x 1.25mm but threaded all the way along the shaft of the screw) from THE INSIDE of the crankcase. Put a flat washer, a spring washer under the head of the screw, a bit of loc-tite on the thread and do the screw up TIGHT. Again,use 2 PLAIN nuts to tighten down the mounting bracket. If you use a 'locking' nut you will run the risk of loosening the screw back out of the crankcase, which will cause an oil leak. If you are able to carry out the "screw from the inside" modification, you will need a couple of screws that are 1-3/4in (45mm) long. If you only use studs (for both top and bottom studs) you should be able to get between 7/8in and 1in (22mm to 25mm) of thread into the crancase--you will then need about 3/8in to 1/2in (11mm to 13mm) of plain shank, depending on the brackets that you are using, and about 3/4ln (19mm) of thread for the 2 retaining nuts and a flat washer. I tend to make my studs from rocker-shaft retaining studs---very easy with a 8mm x 1.25mm die and a couple of nuts that you can lock together and hold the stud (in a vice utilising the 'locked' nuts).Does this help and sound sensible?
'Bakker' (apologies for not knowing your christion name), I have put my thoughts on tuning the 500 and 126 engines down on paper. If you would like to contact me direct ( [email protected] ) and let me know what engine you have in your car, I will send you a copy of the appropriate 'paper'. In the 'paper' there is a description of this modification which are very welcome to have as an "aid memoir"
