LAST EDITED ON Jul-18-01 AT 10:15 AM (EST)>I have struck a deal for,
>but do not yet have
>possession of, a runout baffle-piston
>OS .40 (40S?) ballbearing r/c
>engine (not enough compression to
>support a reliable idle).
>I know where I can
>get an appropriate venturi, nva,
>bearings, and a ring, but
Peter;
A couple of things on the Max-H 40. Firstly, a ring replacement is usually all you need to get one of these to restore compression. Frank Bowman makes replacement rings for these engines at minimal cost. Frank or Leonard can get/make for you a venturi (Leonard's works well on my Max-H 40). Leonard also has long ST type NVAs that worked well on my Max-H 40s.
The only things that I would worry about is the shape of the crank bearings and any conrod/wrist pin play. A way to check the conrod/wrist pin is to give the engine a good shot of oil to help seal the compression better. Turn it over by hand. As you come past TDC, you shouldn't feel much play between push and pulling the piston. The Max-H 40 had a bushed conrod, and they usually hold up well. If there is a lot of click, the engine needs a new conrod, and there aren't too many of them out there for sale. As for the crank bearings, that is a more subjective call. I have one Max-H 40 that felt rough when I got it, but a little running and it was just fine.
Total cost to convert this engine (with venturi, NVA, and new ring, plus postage) will run between $30 - $45. Add that to the cost of the engine outright. You will have to make the call if this is worth the cost to convert or to buy a new engine. If you do decide to get it, I am not sure what kind of fuel most will recommend, but I like 5% nitro and 25% all castor lube fuel. These older engines don't always hold up well with the synthetics or synthetic blends. Lost compression now due to synthetic lube and low lube content/percentage could be the reason the engine is getting weak on compression. All castor is messier, but the engines seem to hold up.