OS FS 90 - One of Max's early four strokes

Hi Bob , she is looking much better in your hands , I have never seen one of these engines taken apart and the insides , don't look too bad what's the valve lash on that puppy ? I have a OS 45 OHV brand new . Is this the epoxy your going to use ?  http://www.loctiteproducts.com/p/epxy_weld_t/overview/Loctite-Epoxy-Weld-Bonding-Compound.htm  I hope you can get it squared away >> like to see it run if possible. Eric

Not sure if Epoxy will work, it usually breaks down quickly with heat. Although JB is epoxy based so who knows.

Can you get someone willing to TIG weld it?

I didn't see any piston pictures, is it a ringed piston? Dykes ringed engines will not develop good compression until warmed and running.

Ron

"Techno-Weld" might be a suitable product for this.

http://www.techno-weld.co.uk/home.html

As Karl mentions, that can be repaired with "Techno-Weld" - I use it quite a lot for repairing crankcases. Mostly mounting lugs or busted venturis.

It needs a great deal of practice though! The melting point of "Techno-Weld" is only a smidgen off the melting point of most castings. Although they state that it is 200 deg less than aluminium. I use a small butane torch for repairs like this.

You have to "tin" both surfaces by simultaneously scratching the surface of the casting/aluminium with a stainless steel brush or sharp stainless steel pointy thing. I use tattoo needles. The "Techno-Weld" needs to penetrate the oxidised surface.

Once the parts are tinned - they can then be braised together.

This will produce a repair stronger than the original but, as I say, you have to be aware that the casting/aluminum must not melt. The "Techno-Weld" melts at 380 deg C and aluminium at anything up to 600 deg C. But when you are heating small parts with a torch to tin them - it only takes seconds to overdo it! The thinner the part - the harder it is to get it right!

The broken boss is ONLY a hard point for a post that holds the carb in relation to the intake runner

I would be tempted to grind it out of the way and fabricate a rear cover plate to hold the carb and bend a copper tube to mate back to what ever the new out of alignment position of the carb is

Thanks for the pointers and replies.  I will check them all out.  But, my goal is just to get it running, I don't have anything large enough to mount that lump on.  Maybe some day if it runs well.

But, hooray I now have gobs of compression.  I removed the rockers closing the valves but still no compression.  Had to anyway to get to the just snugged head bolts.  I tightened the head bolts and dropped some light oil in the glow plug hole and wow, there it is.  I thought I had it timed right and I did.  Now to replace the rockers and reset the valve lash. .1 mm I think, got to check it again.  



It is a ringed piston.  Fingernails come in handy when compressing for reentry.  I don't think the piston/con rod are directional, but just to be sure I center punched the outside of the rod just to be sure it went back in the same way.  



Mainly just a learning experience, I have never re-built one of these.  Very interesting.......





When I get it running I will post a video if my son's around with his "smart" phone.  I don't have one of those little walk-around marvels....or have a need to.  

BTW, I did not remove the valves. Looking at those little tiny C clips I realized that with my shaky hands I would never be able to get them back on, and if I lose one.....But I went to great pains to clean the seats in place holding the valves open while using hot AF/Simple Green and an assortment of brushes.

I have the early open rocker OS FS60. It states zero valve lash when cold. The gap opens with heat. Also, I would have thought that the carb "mount" was actually an induction port into the crankcase to allow some lubricating oil/fuel mix in. Otherwise, how is the bottom end lubricated?

Oldenginerod wrote:I have the early open rocker OS FS60.  It states zero valve lash when cold.  The gap opens with heat.  Also, I would have thought that the carb "mount" was actually an induction port into the crankcase to allow some lubricating oil/fuel mix in.  Otherwise, how is the bottom end lubricated?

These actually came with two feeler gauges a .04mm to set the lash and a .1mm to check it.  

Good question,  I always thought those larger holes in the piston were for lightening, but they also may assist in transferring lubrication to the bottom end.  ????

Youtube video. He mentions a .004 feeler then corrects himself to .04. Good series he gives on these, both dis and reassembly.

https://www.youtube.com/watch?v=8BgVVuSSQvY

Bob

Cool, the OS 90 was a good runner not as much power as the newer surpass series but still had nice running qualities.
One thing I would do is check bearings and the tappets (Cam followers) for pitting Four strokes run on a high synthetic oil diet so they are more susceptible to rust and corrosion and the tappets tend to get the brunt of the rust. About how they lubricate, Four strokes lube through piston blow by which is why they have a thin ring. About the fuel, run a high synthetic based fuel around 10-20% nitro. high castor fuel is not good for then because it tends to block them up when cold and since they run hotter varnish can be a problem. (Bandit)

Looking at Bob's photo of the inside of the head "before", I'd suggest someone must have been using castor. There's an awful lot of cruddy build up there. Shouldn't get that on synth.

Yeah it appears that it was run on heavy castor from the carbon buildup in the combustion chamber. It cleaned up nicely though and the bearings don't look too bad. BTW if you haven't run a four stroke before, make sure that you don't block off the breather, if it gets blocked off, it won't lubricate. (Bandit)

The bearings are quite good. The A/F boil followed by careful in place cleaning with Simple Green did wonders. A little light oil and they are silky smooth. The followers the same, looked as new after cleaning.

The cylinder liner amazed me, came right out with little effort. Almost no varnish inside or outside but that top end sure was nasty. I'm used to heat gun then using the piston leveraged against the buildup at the top of the cylinder to pop it out.

All I have in addition to my Cox fuels is 20% with added castor. I am going to snug the case screws up tight then try to get it to run as is before tearing it all down again, cleaning then replacing the O rings (waiting for new ones) on the outer push rod covers and applying gasket RTV to the case surfaces. After that, a shelf queen/serf until I find a use for it.

Bob

Well I'll be darned.  One flip and it started.

Three turns out, running pressure, primed through exhaust port, unsecured throttle and fuel tank, leather gloved hand flip and it started running rich at thankfully low RPM's.  I hadn't planned on it running, I would have been happy with a pop. We didn't even get that when we first started with it a few days ago.  Needled it off.  

Not proud of this picture, not the way to do it.  What would have happened if it started at full throttle......



Checked it out and found that the exhaust rocker had loosened up.  It's hard for me with shaky fingers to hit that little hex hole in the screw while trying to lock down the lock nut.  Takes three hands,  I used my chin to hold the allen wrench in place.  

Got it secured now, but after cutting up a couple of cedars this morning I'm just to spent to start it again.  A shower and lunch followed.





Bob

Good work, Bob. Now I know more about four stroke model engines than I did... which was nothing. Not much more now, but thanks for an interesting thread.
Rusty

RknRusty wrote:Good work, Bob. Now I know more about four stroke model engines than I did... which was nothing. Not much more now, but thanks for an interesting thread.
Rusty

Your welcome Rusty, anytime I can add to the knowledge of our local CEF genius I'm feeling pretty good.

I was checking though ebay's offering of four stroke glow plugs and came up with this from Omni models



It looked familiar, then I remembered that I had substituted a different glow plug from the one that came on it with one from my spares.  I did it because I couldn't find the gasket (which is probably on the bottom of my A/F pot).  So I sort through the junk on my workbench, found the original plug and replaced it with the gasket, ought to run better now.  A different look to the four stroke plugs.



Also, the O ring kits arrived. Fast shipping from the vendor was appreciated.  My old kits are well picked over so new ones were necessary, both metric and SAE for less than $20 shipped.  The smallest metric (marked .006mm) are perfect replacements for the outer push rod covers on the FS 90.





Neat way they designed the boxes, space saver as one size fits inside the other when closed.

Car show today, may get it running again tomorrow.

Bob

Bob please post a link to the O ring vendor...I have been needing both those kits

fredvon4 wrote:Bob please post a link to the O ring vendor...I have been needing both those kits

Here ya go..........

http://www.ebay.com/itm/262053495426?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Added to my watch list!
Me being the "Local CEF Genius" I can't believe I don't already have one. Really, Bob, that's too much, as I am quite the doofus Lol. A fun loving funny doofus, but never the less. I bet I've made more members sprain their eye-rolling muscles telling and re-telling me how to do stuff as I either resist or forget. Just ask my patient friend Ken... no, he'd never say it. Anyway, thanks for the gracious comp.

Why you not got the Muffler on it ?? I am happy to hear she fired up for you . That's a killer deal on the O- Rings !!

getback wrote:Why you not got the Muffler on it ?? I am happy to hear she fired up for you . That's a killer deal on the O- Rings !!  

Ya, Fred and I will be supplying the neighbors with O rings for years to come. It aways seemed that I didn't have the O ring size that I needed on hand, now with all these standard sizes we will.

I left the muffler off so I could prime it. With the way I had it configured I could not get a finger over the carb venturi to prime it that way by pulling the prop through. But it sure filled the supply line in a hurry once running. Got a nice little bark to it without the muffler.

Ya can't hide it Rusty, your videos, your prose, your character.....pure genius....

Bob

ARRG !!! Count me in too!!! Durn PayPal gonna be smokin' !!!!!

Gadget Bankrupt Kim

Did I mention that I expect a gratuity for each one sold..................    

The perspicacious Bob