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    Old Saito 40 lost compression after attempted cam replacement

    I tried the "heart transplant" suggestion for improving an old Saito 45, but tried it on my old Saito 40 instead. I thought it ought to work because the 40 looks identical to the 45 and even has the "40" printed on a metal tape over what was probably a "45" on the case.

    Unfortunately it didn't work because the larger cam would not turn inside the cam case. There wasn't enough clearance for it to go around.

    But now I have a new problem: After the attempt the engine completely lost all its compression. I was using the Higley book and thought I did everything right. The rockers move up and down, and I'm pretty sure I got the mark on the cam lined up correctly with the gear on the crank (it's hard to do because the whole thing becomes impossible to see right at the moment when you would like to watch it as it goes together).

    Anyone have an idea about why I lost compression?

    Jim

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    SrTelemaster150's Avatar
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    RE: Old Saito 40 lost compression after attempted cam replacement


    ORIGINAL: buzzard bait

    I tried the ''heart transplant'' suggestion for improving an old Saito 45, but tried it on my old Saito 40 instead. I thought it ought to work because the 40 looks identical to the 45 and even has the ''40'' printed on a metal tape over what was probably a ''45'' on the case.

    Unfortunately it didn't work because the larger cam would not turn inside the cam case. There wasn't enough clearance for it to go around.

    But now I have a new problem: After the attempt the engine completely lost all its compression. I was using the Higley book and thought I did everything right. The rockers move up and down, and I'm pretty sure I got the mark on the cam lined up correctly with the gear on the crank (it's hard to do because the whole thing becomes impossible to see right at the moment when you would like to watch it as it goes together).

    Anyone have an idea about why I lost compression?

    Jim

    If you got the lifters, pushrods or rockers switched around, you will have to check for adequate valve lash. One of the valves is probably not closing all the way.
    Club Saito #785 - FA91S, FA150, FA180, FA180HC/BBC, FA200TI, FA300TTDP: All with CH Ignitions CDI/Glow fuel
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  3. #3

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    RE: Old Saito 40 lost compression after attempted cam replacement

    Ah, I only took out the pushrods, but I could easily have switched them. I'll check the clearances. The lifters stayed inside the boots, and I didn't touch the rockers.

    I took apart as little as possible. First I took off the carb and inlet tube, then loosened the cylinder bolts, and then the cam housing bolts. Then I finished taking out the cylinder screws and lifted the cylinder off just enough to get the pushrod tubes out. Then I took off the cam housing and got the cam out. At some point the push rods fell out.

    Thanks, I'll go back and check the valve lash.

    Jim

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    RE: Old Saito 40 lost compression after attempted cam replacement

    Jim, I had a Saito 40 with broken mounting lugs. I found a crank case on Ebay and picked it up. Everything looked OK, but when I assembled it, two issues showed up. The cam was binding on the crank and the crank pin was scratching on the back plate. I ended up cutting some shims from a coke can for both the cam cover and the back plate. That cured the binding.

    Timing the cam can be a bit of a problem, espically with the shim I made. I found that if I took a piece of packing plastic, a flat onenot more than 0.010 thick, and made a horse shoe, U , shape the would just fit the width of the minor diameter of the cam gear. I could lock the cam gear timing and that simplifyed trying to hold the gear in place while dropping it onto the crank. My old 40 ran like a top after. Getting the timing correct can be a pain. But it has to be right before woring about valve clearance. Make the plastic narrow enough that the screws will miss it, but tight enough to the cam to keep it from rotating. It slips on from the front, so once you have the cam lockedand set on the crank case, you simply slideit out from under the coverand then screw the cover down. Once you have the cam cover on and know it is in time, then check the valve lash. 0.002" go, 0.004" no go at TDC on the compression stroke, Getting the pushrods swapped shouldn't make a big difference. they are interchangable as the length is the same, but one could be slightly more worn that the other. A quick adjustment is all that is required to set things straight.

    Don

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    RE: Old Saito 40 lost compression after attempted cam replacement

    ive had that problem before on ringed engines.... make sure the timing is right and valve gap/lash and fire it up....that ought to bring the compression back up
    \"Propellers are notorious for inflicting serious bodily harm while vigorously defending their space\" George Aldrich

  6. #6
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    RE: Old Saito 40 lost compression after attempted cam replacement

    I can check the valve timing with the engine all assembled and in the plane

    Or by taking the valve covers off and looking at the rocker arms.

    Also if you are feeling of compression, you must have the carb fully open.

    Find Top Dead center on the compression stroke.

    Turn the crankshaft 360 degrees. Both valves sould be open. You can blow through the exhaust and out through the open carburetor. Or take off the valve covers and see where both rocker arms a parrallel across their tops. This parrallel point is usually about 5 degrees before top dead center.

    Fact is . . . the overlap must pass through top dead center on the overlap stroke.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Very helpful everyone, I got the compression back...whew! I like Campgems idea for keeping the cam from moving while installing it. But I think I got it right. Here's what happened:

    I discovered both valves were very tight. I don't know how that happened. They were right before I started, and wrong when I finished assembly. I never touched the rockers or the adjustments. But as soon as I got the valve lash right the compression came back.

    That still leaves the timing. I think it's OK, but please tell me if this sounds right. I'm turning the crank counter-clockwise, the same way it runs. Just after compression the exhaust valve opens. As I continue turning, the intake valve starts to open just as the exhaust valve is closing. The intake valve continues to open, and then closes and at that point I start feeling compression again. Sound OK?

    Thanks for all the help. I think the Higley book taught me just enough to get into trouble.

    Oh, one more thought. Tell me if this is a really bad idea. I was thinking of using my Dremel to cut enough clearance inside the cam housing to allow the bigger cam to rotate. Forget it, right?

    Jim

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    RE: Old Saito 40 lost compression after attempted cam replacement

    Actually, I think I can just get a new cam housing from Horizon, the one for the 40S, 45S, 50, 56 etc. http://www.horizonhobby.com/products...ii-jj-SAI5033A

    That should fit my engine and allow me to put in my cam, right? They only cost 7 bucks.

    Jim

  9. #9
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    RE: Old Saito 40 lost compression after attempted cam replacement

    ORIGINAL: Campgems

    Jim, I had a Saito 40 with broken mounting lugs.Β* I found a crank case on Ebay and picked it up.Β* Everything looked OK, but when I assembled it, two issues showed up.Β* The cam was binding on the crank and the crank pin was scratching on the back plate.Β* I ended up cutting some shims from a coke can for both the cam cover and the back plate.Β* That cured the binding.Β*

    Timing the cam can be a bit of a problem, espically with the shim I made.Β* I found that if I took a piece of packing plastic, a flat oneΒ*not more than 0.010 thick, and made a horse shoe, U , shape the would just fit the width of the minor diameter of the cam gear. I could lock the cam gear timing and that simplifyed trying to hold the gear in place while dropping it onto the crank.Β* My old 40 ran like a top after.Β* Getting the timing correct can be a pain.Β* But it has to be right before woring about valve clearance.Β* Make the plastic narrow enough that the screws will miss it, but tight enough to the cam to keep it from rotating.Β* It slips on from the front, so once you have the cam lockedΒ*and set on the crank case, you simply slideΒ*it out from under the coverΒ*and then screw the cover down.Β* Β*Once you have the cam cover on and know it is in time, then check the valve lash.Β* 0.002'' go, 0.004'' no go at TDC on the compression stroke,Β* Getting the pushrods swapped shouldn't make a big difference.Β* they are interchangable as the length is the same, but one could be slightly more worn that the other.Β* A quick adjustment is all that is required to set things straight.Β*

    Don

    Even though the pushrods are theoretically the same length they can & do sometimes slightly vary, especially after being used for some time. There is also the relationship of the interface on the tappet & rocker arm that can induce changes in the shape of the junction to further influence valve lash.

    I have often had to re-adjust valve lash when getting pushrods swapped.

    All of the above can be said for every component in the valve train. Tappets, rocker arms & the individual valves can all vary slightly in length, especially when they have been in service for a long time..

    However, in the OP's case, both valves having insufficient valve lash is a mystery. Ususlly mixing up the pushrods has resulted in 1 cylinder W/excessive lash while the other was tight.

    Your timing fixture trick is useful & I use a similar jig on my big block singles that have nailhead shaped tappets & it will work on any Saito engines.

    On the small & medium sized singles W/the tappets that are cylindrical, the cam can be held in time W/a pin inserted through the intake lifter tappet bore into a hole in the intake lobe of the cam.



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  10. #10
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Jim,

    There is a small gasket under the cam housing that is very important. You need this and may have overlooked it.
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  11. #11
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    RE: Old Saito 40 lost compression after attempted cam replacement

    ORIGINAL: blw

    Jim,

    There is a small gasket under the cam housing that is very important. You need this and may have overlooked it.

    I've heard that sometimes adding an additional gasket or 2 can also help when the gear lash is really tight.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Thanks blw. I recall a gasket under the cam housing that just looked like the foot print of the housing. Is that what you mean? If so, it's still there. I worked in a clean place and didn't wind up with any extra parts.

    Does it sound like I got the timing gear lined up correctly, from my description above?

    Jim

  13. #13
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    RE: Old Saito 40 lost compression after attempted cam replacement


    ORIGINAL: buzzard bait

    Thanks blw. I recall a gasket under the cam housing that just looked like the foot print of the housing. Is that what you mean? If so, it's still there. I worked in a clean place and didn't wind up with any extra parts.

    Does it sound like I got the timing gear lined up correctly, from my description above?

    Jim
    To double check the timing, run the engine up on TDC on the EX/IN cycle (360* from TDC compression) before you put the rocker covers on.

    When you rock the crank back & forth @ TDC you should see both rockers moving equally in opposite directions. They should both be slightly down (valves slightly open) @ TDC.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Yes, that's what they do, thanks.

    I'm going to get a cam housing to fit the cam. I've come this far, I gotta see what happens!

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    RE: Old Saito 40 lost compression after attempted cam replacement


    ORIGINAL: buzzard bait

    I'm going to get a cam housing to fit the cam. I've come this far, I gotta see what happens!
    Just make sure the new cam housing type is not for the new high case. Your's is probably the old half-circle low case type.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    I'm getting the one that says it's for a 40S, 45S, 50, 56, etc. Old style.

    The gasket set for the old FA-40 also works for the old 40S, so the cam housing that fits the 40S etc. should fit the FA-40, right? Since they both use the same cam housing gasket.

    Jim

  17. #17
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Putting something wood like a toothpick resting on the piston crown thru the glow plug hole may make it easier.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Make sure you have the pushrods in right side up too, the smaller tapered end must go toward the rocker arms. If you reverse them it will affect the clearance and over time will break out the sockets in the adjustment screws.
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  19. #19
    SrTelemaster150's Avatar
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    RE: Old Saito 40 lost compression after attempted cam replacement


    ORIGINAL: bigphil

    Make sure you have the pushrods in right side up too, the smaller tapered end must go toward the rocker arms. If you reverse them it will affect the clearance and over time will break out the sockets in the adjustment screws.
    Oh wow, I'm so used to working on the big blocks that I forgot all about that.

    Yes, while the 120/150/180 have pushrods that are the same on both ends, the smaller engines have a definate top & bottom to the pushrods.

    That might explain BOTH cylinders having no lash.
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    RE: Old Saito 40 lost compression after attempted cam replacement

    THANK YOU! I could not see any difference when I put them back in. I'll have to inspect it closely when I get the new cam housing and do the process all over again.

    Jim

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    RE: Old Saito 40 lost compression after attempted cam replacement

    I got the new cam housing from Saito and sure enough, there is a subtle difference in the interior that allows the larger cams to turn! Cold and windy out right now, but I'm excited to do a test.

    Thanks to Big Phil, I have the pushrods in the correct way now.

    Just to be clear about what I found, here is what happened: I tried to hop up an old Saito 40 with a cam that is listed for the 40S, 45S, 50, and 56 engines. The problem is that the new cam wouldn't turn inside the old cam housing. So I bought a new cam housing that is listed for the same engines the cam was listed for. That gave the clearance and also fit my engine. So in theory, I should have the equivalent of a 40S now, with more power.

    Only thing that doesn't quite fit right is the little rubber booties that go over the base of the push rod tubes. They are too short now, because the brass stubs that hold the cam followers stick up farther. I just positioned the booties so they seal the place where the push rod tubes go in. There's a gap at the bottom now, so I suppose the potential problem is that they could slide down. I really don't want to place a third order to Horizon and pay shipping again. There's enough friction I doubt they'll slide down.

    Will give a test report when I get a chance to fire it up!

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    RE: Old Saito 40 lost compression after attempted cam replacement

    Rats!! I spoke too soon. The push rod tubes don't fit because the the brass guides in the new housing for the cam followers stick up too much. So now I need shorter push rod tubes. Cut them down? But then I'm committed. If something else about this experiment doesn't work I can't go back to the old engine as it was.

    Can I make push rod tubes from aluminum tubing? Wall would be thicker, but I think there would be enough clearance.

    Man, this thing sounded so simple in the beginning...

  23. #23
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    RE: Old Saito 40 lost compression after attempted cam replacement

    I would say the aluminum tubing should work. Check to make sure the pushrods don't drag through a complete two turn rotation of the engine. The pushrods don't stay precisely centered in the tubes due to the geometry of the rockers, they MUST swing very slightly fore and aft. If they don't touch your aluminum tubes, then I'd say give it a try.

    Actually you could give it a brief test run without the tubes in place. It might sling a little oil from the lifters but won't hurt for a test run. Not good for the long term because oil is supposed to travel through the tubes to lube the rockers.
    Big Phil
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    RE: Old Saito 40 lost compression after attempted cam replacement

    Ah, I was wondering if it would be OK to run it without them, and then I got to wondering about their purpose.

    Unfortunately the usual tubing dimensions are wrong for the push rod tubes.

    Thanks,

    Jim

  25. #25
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    RE: Old Saito 40 lost compression after attempted cam replacement

    I didn't go back and read all the posts so this may have already been said?

    As for the tubing around the ends of the push rod tubes, you can use most any tubing that willl fit. I bought a Saito with glow fuel tubing on the ends of the tubes. I changed it and put the original type on.

    You can buy new tubes for the 56 and cut them off to fit your 40. Cut them off with the abrasive cut off disk of a Dremel.
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