Hi, I recently got my hands on an unused os max 35 (circa '76). The instructions state 25% castor oil, but can I use a modern fuel with say 16% synthetic and 4% castor or do I need to add castor to the fuel, or what?
Don't want to wreck this motor, so any advice would be really helpful.. Thanks
Phil Myers

Hi Phil  the following is from the fuel article pegged at the top of this forum, you may want to take a look at it

   So what percentage do you try? For motors like Fox .35s, OS Max 35s or the old McCoy’s and K&B’s, use a fuel with 26 to 28% oil content; preferably half castor and half synthetic, up to 75% castor  is OK. These  motors have very small bearing surfaces, and are subject to much wear and heat, most are all plain bushing motors and most have unbushed rods. They need a lot of  oil  to help cool the engines. Since these motors run hot, they need  extra oil to keep them lubed,clean, and to carry out heat . If you have one of these that is  in very good  shape but, is  just starting to get some brown or black varnish plating on it, the synthetic mix will clean it  up for you, resulting in increased life.  Do not use the synthetic  blend in an old motor that has a lot of time on it with all castor fuels; the synthetic will remove the castor varnish off the piston and sleeve and will in some cases, leave you with the worn-out motor that had to start with.  Also always try to NOT use  prop shaft extensions with these engine, as it adds a  lot of  wear on the crankshaft bearing.

Regards
Randy

Randy, thanks for the info; guess I should have read your original article first. There's a lot of information in that post... btw I forgot to mention that I want to use this motor in an s1 Ringmaster (winter project) how do other members on SH think of this match up? Too powerful or about right... once again any comments are much appreciated..Thanks
Phil Myers

I had dozens of S35s  I used the 30S and 35S in my Ring Masters, they worked very well in the plane
YOu can also use an Enya 25 or 30SS or a OS 25LA

Randy

I've got a Randy Smith prepared OS 35S in my Jamison Special, outstanding engine. You might wanna ask about having him do his thing on it since it's new.

Thankyou to all who have posted tips and advice for me.. Phil

Randy, I was told by a very experienced and renowned flier that, back in its day, the OS Max 35's that were competition material had Supertigre rods installed.  Of course, this was a "secret" and the big dogs weren't supposed to reveal the changes they had made.  Any comment?  Is the ST rod still available?

Randy, I was told by a very experienced and renowned flier that, back in its day, the OS Max 35's that were competition material had Supertigre rods installed.  Of course, this was a "secret" and the big dogs weren't supposed to reveal the changes they had made.  Any comment?  Is the ST rod still available?

What Randy said. Also, the fix that Big came up with was to use the stock rod with the venting Randy speak of as in oil holes and slots in the face of the rod where it contacts the crank. The big mod that saves the whole reciprocating/rotating bits is to limit the crank end play. Big made a teflon button that located in the hollow crankpin hat limited the end play to .015" to .020" The crank bouncing back and forth in the stock setup puts big time bending loads on the wrist pin and rod bearings. Limiting the movement limits the loads.

I hesitate to take my OS 35S apart and mess with the con rod or the wrist pin ends.  However, if it will make it last longer, I will do it.

GMA once reported putting aluminum rivets into wrist pins.  Some of my engines use wrist pin pads: the Orwick uses brass discs (which are easily lost when taking it apart).  Most wrist pin pads don't fall out, so I don't worry about them.
Floyd