OS 61. Which one should I avoid?

[David Davis]

I am interested in acquiring a good used OS 61 two-stroke to suit a Supra Star which I will build once it comes to the top of the pile!

 

I already have a 61 SF which is a delightful engine and destined for DSM Aerostar once I get round to refurbing it.

 

Since the production of the SF ceased, OS have produced the FX and AX range.

 

Wasn't there a problem with chrome plating peeling on the liner of the FX engines, or was it the AX range? I haven't kept up with the alaphabet soup! 

[Nigel R]

Keep your eyes peeled for a nice 61SF on ebay, would be my suggestion. They are, as you noted, very nice.

 

 

[Engine Doctor]

I have an Fx with the chrome shedding problem in my spares / junk box and parts prices to fix it , if they were available are just too high.  Stick to an SF . They are good dependable engines made before OS out- sourced the plating to Taiwan . I think it was down to polution laws and like many businesses around the world OS  moved the process to a country who dont worry about poluting the planet . Anything later than SF are prone to the chrome peeling issue . Not sure about the larger engine range though. I have a OS 160 AX to strip and clean and fit new bearings and hope cylinder is OK . You cant tell by feeling compression as in early stages  of chrome peeling the compression will stil feel fine. If it must be an OS for you , ask if you can remove head and check around top of cylinder aand cylinder walls before parting with cash. We refer to it as chrome as in ABC construction but its called Nickasil plating so assume its a type of Nickel.

Ive never sèen a ASP, SC etc with peeling chrome, even MDS got it right although they both had other issues. 

[Nigel R]

The SF do also have plating issues. Buyer beware, etc. I have several 61 SF bought from second hand sources that had peeled liners. I read that Nickel plating requires a higher degree of both workshop cleanliness and chemical bath purity and OS struggled with that. The other manufacturers were not restricted by tighter environmental laws regarding chrome.

 

Of course OS did also use ringed pistons, I guess that wasn't fashionable, very few second hand engines have ringed setups. I do have a ringed SF, they are out there, and it runs just the same as the ABC one. The heli engines are a reasonable source of ringed piston/liner combos, if needed.

[Andy Stephenson]

There's a guy in Australia called Brian Gardner who specialises in replacement piston and liner sets for OS 61 SF and RF engines as they both suffer with the peeling problem. His products are absolutely superbly engineered. They are properly chromed and they come with con-rod fitted and a gasket set. I have two of these sets for my 61RFs after experiencing the problem. He does a run of about 50 or so at a time and he has a waiting list. He also does replacements for 61 FSR and 61VF engines. If you need to revive one of these engines to better than new running order you can get your name on the list at...

https://www.rcgroups.com/forums/showthread.php?3380853-Making-ABC-piston-liner-rod-pin-sets-for-O-S-61SF-RF-engines-(tally-in-OP)

 

[Paul De Tourtoulon]

Do you have to go with an OS ?.

 

I have had plating issues with Magnum and  Thunder tigre due to overheating on people who run them in on the bench, I have had both OS and Irvine

chrome peeling problems, there are other older engines that have never ( my experience) had any of the above problems, HP, Webra, Enya, K&B, Supre Tiger, and lastly my favourite, Rossi.

[Kevin Fairgrieve]

This came out of an FX

 

Substituted with an ASP liner.

 

Still going strong!