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OS FS 90 - One of Max's early four strokes Babe_b10
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OS FS 90 - One of Max's early four strokes Empty OS FS 90 - One of Max's early four strokes

Post  rsv1cox on Thu Jul 07, 2016 7:02 am

My son who used to bring home kittens now brings dead or half dead glow engines.  I can't fault him though, as a kid I once brought home a dead cat, seriously.  But that's another story.

$30 at a flea market.  Crashed engine with a JB welded repair.

OS FS 90 - One of Max's early four strokes Geese_11

OS FS 90 - One of Max's early four strokes Geese_10

No compression, both rockers moved in unison, severely out of time.  Into the A/F pot.

OS FS 90 - One of Max's early four strokes Os_90_13

OS FS 90 - One of Max's early four strokes Os_90_10

OS FS 90 - One of Max's early four strokes Os_90_12

OS FS 90 - One of Max's early four strokes Os_90_11

OS FS 90 - One of Max's early four strokes Os_90_14

Cam followers are little hammer shaped things.  Easy to remove, a pain to get back in.

OS FS 90 - One of Max's early four strokes Os_90_15

OS FS 90 - One of Max's early four strokes Os_90_19

OS FS 90 - One of Max's early four strokes Os_90_18

OS FS 90 - One of Max's early four strokes Os_90_17

I'm not sure how to repair the broken carburetor mount.  The JB Weld went away in the boiling pot.  It's a poor design eliminated in the later OS 91 Surpass, meant to be friction secured by a machine screw.  I'm thinking epoxy would work as well.  No parts are available for this old timer so I will have to use gasket blue RTV on the cases.

Everything is just test fitted now, it will have to be completely disassemble and do a final cleaning in alcohol.  But I timed it by the book and no compression, so I will have to revisit that again.  But I didn't torque the head down either, so that may be a factor.  Setting the valves was easy though and now they both operate sequentially.  Fun and games.

Bob
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Post  Kim on Thu Jul 07, 2016 8:24 am

COOL!!!!

"Bob...Savior of Busted Kittens"

Hope you can get it going!
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Post  getback on Thu Jul 07, 2016 9:16 am

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 This Site Rocks!
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Post  Cribbs74 on Thu Jul 07, 2016 10:48 am

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
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Post  KariFS on Thu Jul 07, 2016 11:36 am

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

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

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Post  ian1954 on Thu Jul 07, 2016 1:47 pm

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!



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Post  fredvon4 on Thu Jul 07, 2016 2:40 pm

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
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Post  rsv1cox on Thu Jul 07, 2016 3:46 pm

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.  

OS FS 90 - One of Max's early four strokes 90_lat10

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.  

OS FS 90 - One of Max's early four strokes Os_90_20

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

OS FS 90 - One of Max's early four strokes Os_fs_11

OS FS 90 - One of Max's early four strokes Os_fs_10

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.   Smile

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.
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Post  Oldenginerod on Thu Jul 07, 2016 5:50 pm

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? Huh...
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Post  rsv1cox on Thu Jul 07, 2016 7:14 pm

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? Huh...

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
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Post  TDbandit on Thu Jul 07, 2016 8:07 pm

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)
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Post  Oldenginerod on Fri Jul 08, 2016 1:39 am

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.
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Post  TDbandit on Fri Jul 08, 2016 2:23 am

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)
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Post  rsv1cox on Fri Jul 08, 2016 6:22 am

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
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Post  rsv1cox on Fri Jul 08, 2016 10:25 am

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......

OS FS 90 - One of Max's early four strokes 90_st_11

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.

OS FS 90 - One of Max's early four strokes 90_st_10

OS FS 90 - One of Max's early four strokes 90_st_12

Bob
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Post  RknRusty on Fri Jul 08, 2016 11:02 am

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

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Post  rsv1cox on Sat Jul 09, 2016 6:39 am

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. Smile

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

OS FS 90 - One of Max's early four strokes Os_fs_12

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.

OS FS 90 - One of Max's early four strokes O_ring10

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.

OS FS 90 - One of Max's early four strokes O_ring11

OS FS 90 - One of Max's early four strokes O_ring12

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
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Post  fredvon4 on Sat Jul 09, 2016 7:59 am

Bob please post a link to the O ring vendor...I have been needing both those kits
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Post  rsv1cox on Sat Jul 09, 2016 8:17 am

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
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Post  RknRusty on Sat Jul 09, 2016 8:55 am

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.

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Post  getback on Sat Jul 09, 2016 10:09 am

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 !! United States
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Post  rsv1cox on Sat Jul 09, 2016 11:43 am

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 !!  United States

Ya, Fred and I will be supplying the neighbors with O rings for years to come. Smile 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.... Smile

Bob
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Post  Kim on Sat Jul 09, 2016 12:06 pm

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

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Post  rsv1cox on Sat Jul 09, 2016 12:44 pm

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

The perspicacious Bob
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Post  1/2A Nut on Sat Jul 09, 2016 4:51 pm

Great find and can make wheels out of the big rings 4th of July Flag
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