TheSamba.com :: View topic - How do you find piston size in a 66 beetle?

Thu Jul 02, 2015 7:44 pm

Hello, my name is Nate. I'm 15 years old and recently got my first car, a 1966 VW bug and it has a 40 horse 1200 cc engine, it had a broken ring and a cracked cylinder. holding that someone can point me to a page that has instructions on how to measure the piston size so I can get new rings and cylinders. Thanks in advance for any guidance. -NateG

Fri Jul 03, 2015 4:00 am

In the rare case it's an orig or even of the same yr should be std 77mm dia piston. However po's r famous 4 changing things to keep 'em running. Clean carbon off of top of piston, u will find size stamped somewhere around the edge,could be a non orig 83mm update.

Fri Jul 03, 2015 7:18 am

Roovis wrote: Hello, my name is Nate. I'm 15 years old and recently got my first car, a 1966 VW bug and it has a 40 horse 1200 cc engine, it had a broken ring and a cracked cylinder. holding that someone can point me to a page that has instructions on how to measure the piston size so I can get new rings and cylinders. Thanks in advance for any guidance. -NateG

you can measure across the top of the piston to determine the size. besure the cylinder bores are good, they are a bit tricky to measure with an inside micrometer. If you don't have one of these tools, see about taking the cylinder to a machine shop or VW builder and ask if they can be measured for you. be aware of a cylinder that has a step worn in it. If the old cylinders are good, they should be lightly rehoned before re-assembly.

Note the 1200 motor is not stock to a 1966 Bug USA version. The correct motor should be a 1300cc for 1966.

I was about 15 when I started work on my first Bug, build the motor and tranny. It was a 1961 Bug, I still have that bug over 35 years later!!!!

good luck on your Bug journey, do it right and you to may still be driving your Bug when your fifty!!!!

also the pistons are delicate, so be careful with the new ones, don't let them get dinged or scratched, use care when installing new rings, make sure they fit well in the ring grooves, and you don't ding the pistons installing them.

Tue Jul 07, 2015 7:41 pm

Thank you for the help the piston was marked 82.95, so I'm assuming that means the pistons are about 83 mm. Thanks again NateG

Tue Jul 07, 2015 8:22 pm

So this engine is a 1200 style? It had heads with the "straight up" intake ports?

Also, I could ask about the size of the piston pins, 20mm on the 1200, and 22mm for 1300 to 1600.

If so, then with 83mm, you have a "big bore" kit. (1385cc instead of 1192cc) Depending on who made it, it may have the same size rings as the 1500 engine, or it may not. You'll need to measure how thick the three rings are.

As for the bad cylinder... you may have trouble finding one that exactly matches it.

Replacement big-bore 40HP piston/cylinder kits can have problems, the pistons (usually just #3) can hit the engine case. More on that here:

http://www.thesamba.com/vw/forum/viewtopic.php?t=129792&

-Andy