this is probably a stupid question, but i need to know.

I will be rebuilding my 350 Ody this winter and need to know what size piston to get.

The Engine is stock and i believe has never been rebuilt, but still runs pretty good.

I believe I'm overdue for a rebuild so if anyone can help me out i would appreciate it.

Hi, the only dumb question is the question not asked...


You will need to disassemble your Engine then verify its current condition then take accurate measurements to determine the size piston you will need.

If you go through the service manual it shows you in detail how to inspect.

Also check this out I typed out some details on piston to cylinder clearance, http://pilotodyssey.com/PO/viewtopic.php?t=3115

Ok sounds good. i will try that and get back with any questions.

thank you!

Please ask lots of questions before you start wrenching.

You know how to pressure test a 2 cycle Engine before you take it apart to see if it has any air leaks?

not at all. i found a really good quality online service manual though. will that tell me?

You wont find the pressure testing details in manual that's one of the reasons for this site, tips and tricks, enhancements not found in the manuals.

I havent seen a quality online manual yet all the ones I have viewed show about 50% of the detail found in the printed manual, when disassembling or assembling your Engine it is real important you can see the details of the parts your working on.

Air leaks are not good for engines not only because it allows a unfiltered path for dirt and water into your Engine it allows un-metered air into the Engine when air enters the Engine that has not been through the carb it upsets the air to fuel ratio allowing more air than intended creates a lean condition, a lean condition creates more heat and can lead to a piston seizure or detonation, both are deadly to an Engine.

To test for leaks you pressure test the Engine, you block off the intake where the carb enters the Engine and the exhaust at the manifold the gently pressurize the Engine to see if it holds pressure.

I have found a PVC pipe cap fits nice into the intake manifold then you can use a hose clamp to keep it in place, in most retail plumbing departments you will find a expanding rubber plug that fits the exhaust manifold, you can make up your gauge and required fittings to introduce and monitor the air put in the Engine.

Check out this link this is my tester years ago I used a flat plate with rubber to cap the exhaust http://pilotodyssey.com/rebuild1.htm

A word of caution you need to be careful how you pressurize the Engine you don't want to blow out the crank seals you want to build pressure to 10 lbs slowly, the Engine should hold 10 lbs for 10 min minimum most engines I have rebuilt hold 10 lbs over night with no pressure loss, if you note any noticeable pressure drop you should investigate to see where its leaking, use fantastic or 409 cleaner spray it on the Engine look for bubbles, find the leak, start looking at your connections to ensure your plugs are not leaking.