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OS70 Ultimate FS


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Dave Sanderson07/01/2009 12:55:00
7 forum posts

I need to replace the internal parts of the pump holder assembly which have became dislodged due to the length of time it has taken for the spare pump holder to arrive from Ripmax.

I have asked the Ripmax engineer but, he told me he did not know!  If I had asked RCV for this type of help/information they would have found it for me.

There are 3 internal parts and a spring to the pump.  The first part and the spring is quite straight forward to replace, the next 2 parts consists of 1 round plastic disc and 1 thin round gasket, this is where the confussion lies can anyone please advise on how to replace these parts.

Braddock, VC11/01/2009 16:48:00
1654 forum posts
82 photos

Go to the OS website and you should be able to get a copy of the exploded view of the unit.

Oops, checked it out and there's no exploded diagram of the pump, the engine doesn't seem to be available any more, either.

Dave Sanderson11/01/2009 17:36:00
7 forum posts
I've tried the website and as you said there is no exploded view of the pumps internals.  As far as I now know the pump now only comes in 1 whole unit with a different stock code.  It also looks like this engine is being discontinued, since I have been asking for help on this engine I have learned from others who own one is that it is not a great preformer eg running hot difficult to start, I just thought I had not set the engine up correctly.  Anyway I have a basic idea on the sequence to which the pump parts go back together so I will just give it a go.  Nothing to loose apart from £275.
Engine Doctor17/01/2009 10:34:05
2508 forum posts
39 photos
Hi Dave . Two members of our club bought the 70 Ultimate when it fist came on the market some time ago . They very quickly blew holes in the pistons! The parts were replaced but as you say they were dissapointing and troublesome.
If all else fails , is it not posible to bypass the pump and run with a pressure from the exhaust ?as per Surpass . I know a few guys who couldn't get to grips with the earlier surpass pumpers an converted their engine back to standard Surpass'
Engine Doctor
Dave Sanderson20/01/2009 16:55:25
7 forum posts
Thanks for the ideas.  As I still have all the pump components I will have a try to rebuild the pump first.  I have not had any problems with the piston but I can see how others have as this engine always runs very hot and I never use the engine for longer than 5 minute flights because of this.  If this was a car the manufacturer would have recalled it as defective.  If I was to bypass the pump would I need to change the carb?
Engine Doctor21/01/2009 11:35:26
2508 forum posts
39 photos
Hi Dave . I sholdn't think so . The pump is purely to bring the fuel to the engine , not to fuel inject . e.g If you were flying an aerobatic model with a large tank, the tank could be placed on the C of G  so as not to interfere with the trim of the model as the fuel was used up . This distance required the use of a fuel pump as exhaust pressure was not enough .If the fuel can pass freely through the pump under exhaust pressure then the needle valve will control flow and mixture . As I said earlier many modellers used this technique when they had trouble with or could not set up the earlier mechanical pumps on the surpass engines.The tuning of the mixture controls with the earlier pumps was very sensetive  The only restriction/difference is that the tank will have to be close to the engine and not back on the CG .Fitting a pressure nipple is quick and worth a try and a lot cheaper than the spare parts . Hope it helps
If you really want to keep it as standard then have a look on Tower Hobbies  USA web site  They have very good explode views and parts are a lot cheaper .
Dave Sanderson21/01/2009 22:04:51
7 forum posts
Thanks for the info, I will have a go.

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