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Old 05-28-2020, 04:37 PM
  #46401  
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Originally Posted by FlyerInOKC View Post
Opps! What are you going to do reorder?
Yep, already did. I can use both sizes, and had considered ordering both, but didn't want to spend that much at once, so now I get to pay twice as much for shipping.

AWW CRAP. I just now remembered I had a 5% off code.
Old 05-29-2020, 02:40 AM
  #46402  
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Originally Posted by Hyjinx View Post
Hey Peer Group
Opening a Saito FA 90 T for repair. Any hacks to know on twins?
The left cam timing is different.




They are very different from each other.

Last edited by Hobbsy; 05-29-2020 at 02:44 AM.
Old 05-29-2020, 04:03 AM
  #46403  
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Wow, that left cam is an eye opener for me!

With those lobes having virtually no overlap how can the left cylinder run with the same efficiency as the right cylinder? I'm stumped, never seen that on a multicylinder engine.
Old 05-29-2020, 04:18 AM
  #46404  
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Got the fa180 all cleaned up and ready for the new bearings. This one, like a few others I've seen, has a collapsed exhaust valve spring. Obviously another case of the engine being stored long term on the exhaust stroke.

If you're new to four stroke model engines I should mention, always rotate the engine over until you feel compression before storing your engine for any length of time. The beginning of the compression stroke is also a great position for for a 2 or 4 stroke engine to be in while mounting your 2 blade prop horizontal. With the prop mounted this way if the engine quits in the air the prop will be horizontal on your dead stick landing and have less chance of striking the ground on a rougher than normal landing.

Last edited by Glowgeek; 05-29-2020 at 04:32 AM.
Old 05-29-2020, 04:54 AM
  #46405  
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Originally Posted by Glowgeek View Post
Wow, that left cam is an eye opener for me!

With those lobes having virtually no overlap how can the left cylinder run with the same efficiency as the right cylinder? I'm stumped, never seen that on a multicylinder engine.
I was wondering what the cams would look like in these opposed cylinder designs. Figured the valve timing would be tricky.
Just found a good old thread in this engine. Looks like a lot of help.
Old 05-29-2020, 05:03 AM
  #46406  
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Originally Posted by Glowgeek View Post
Got the fa180 all cleaned up and ready for the new bearings. This one, like a few others I've seen, has a collapsed exhaust valve spring. Obviously another case of the engine being stored long term on the exhaust stroke.

If you're new to four stroke model engines I should mention, always rotate the engine over until you feel compression before storing your engine for any length of time. The beginning of the compression stroke is also a great position for for a 2 or 4 stroke engine to be in while mounting your 2 blade prop horizontal. With the prop mounted this way if the engine quits in the air the prop will be horizontal on your dead stick landing and have less chance of striking the ground on a rougher than normal landing.
The action with the engine running is far more fatiguing than sitting compressed. Think of the coil spring as a torsion bar wrapped up for our convenience.

I will check out my 1.30 and see if has overlap on the left.

Last edited by Hobbsy; 05-29-2020 at 05:05 AM.
Old 05-29-2020, 05:18 AM
  #46407  
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Originally Posted by Hobbsy View Post
The action with the engine running is far more fatiguing than sitting compressed. Think of the coil spring as a torsion bar wrapped up for our convenience.
.............
I won't argue that running the engine promotes valve spring fatigue. Sure it does, especially if the engine is constantly over revved (harmonics) and/or run very hot (annealling), but so does leaving a valve fully open for years during storage.

You don't leave your guns cocked for the same reason. I've replaced more than a few firing pin springs in semi-autos that were left unloaded and cocked in someones closet for years on end.
Old 05-29-2020, 05:25 AM
  #46408  
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That's the reason I rarely use a prop with less than 6" of pitch, those popsickle stick props have no place at my house. On my little 30's I alternate between 10 x 5.5 and a 10.5 x 5. depending on the grass. On an LT 25 the 30 only needs about 3' of take run when using the 10.5 x 5.
Old 05-29-2020, 05:29 AM
  #46409  
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The 120 R-3 sold yesterday and I shipped it yesterday. It went to a great Saito guy.
Old 05-29-2020, 01:39 PM
  #46410  
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I did a check of the left cylinder at TDC between the intake and exhaust stroke and it has overlap in the same amount as the right cylinder. I pulled the cam and made sure the left cylinder had the wide spread lobes and the hash timing mark. I did this on the 1.30 twin.
Old 05-29-2020, 02:10 PM
  #46411  
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Originally Posted by Hobbsy View Post
I did a check of the left cylinder at TDC between the intake and exhaust stroke and it has overlap in the same amount as the right cylinder. I pulled the cam and made sure the left cylinder had the wide spread lobes and the hash timing mark. I did this on the 1.30 twin.
That would seem physically impossible.

Looking at the images of the 90T cams the difference in lobe separation angles is readily apparent and large. Small changes in LSA doesn't always affect the valve overlap period, depends on the lobe profiles but changes that large would certainly show up as a change to the valve overlap period.

That said, the left cam may have been designed by saito to compensate for fueling effeciency problems with the right cylinder, essentially and deliberately reducing the effeciency of the left cylinder to match the right. The left cylinder with the wider LSA would also produce peak torque at a higher rpm than the right cylinder as a consequence.

Last edited by Glowgeek; 05-29-2020 at 02:58 PM.
Old 05-30-2020, 02:41 AM
  #46412  
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I used a long ago suggestion made by w8ye to check the left cylinder overlap and sure enough at tdc between the end of the exhaust and the beginning of the intake the valves alternately open and close. while doing that I discovered that left cam was one tooth retarded. In other words the alternate opening and closing was happening off center with the crank ahead of the cam. That gave me the opportunity to make certain that the left cam was indeed a left cam, and it is. LSA? It would be very difficult to get the cylinders to turn at different rpm for one to peak higher.

You should check a left cylinder cam also and become a believer.
Old 05-30-2020, 04:57 AM
  #46413  
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Nevertheless, having different lobe separation angles between left and right cams as seen in the 90T is not the norm for multicylinder engines. There's some monkey business going on with that left cam and it's cam timing to compensate for something. Admittedly I don't get it.

Heres the cam for the 90TS

Both cylinders run off the same cam on the 90TS and run fine from the reports I've read.

Of course the two cylinders in a twin can't run at different rpm at the same time Dave but each cylinder can and does make different torque numbers at any given rpm. Nothing is perfectly matched between cylinders.

Last edited by Glowgeek; 05-30-2020 at 05:08 AM.
Old 05-30-2020, 05:57 AM
  #46414  
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Originally Posted by Glowgeek View Post
Nevertheless, having different lobe separation angles between left and right cams as seen in the 90T is not the norm for multicylinder engines. There's some monkey business going on with that left cam and it's cam timing to compensate for something. Admittedly I don't get it.

Heres the cam for the 90TS

Both cylinders run off the same cam on the 90TS and run fine from the reports I've read.

Of course the two cylinders in a twin can't run at different rpm at the same time Dave but each cylinder can and does make different torque numbers at any given rpm. Nothing is perfectly matched between cylinders.
Ok guys. I have started a fire again.lol
Being a much less forward thinker than you guys, I simply want to know where what cam timing mark goes where when I am lowering the cam covers to engage the cam gears.
But as usual, I am learning much more than I ever thought when I kindled the embers.


​​​​​

​​
Old 05-30-2020, 06:09 AM
  #46415  
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Originally Posted by Hyjinx View Post
Ok guys. I have started a fire again.lol
Being a much less forward thinker than you guys, I simply want to know where what cam timing mark goes where when I am lowering the cam covers to engage the cam gears.
But as usual, I am learning much more than I ever thought when I kindled the embers.
https://www.rcuniverse.com/forum/glo...lem-print.html


No fires started here Aaron, Dave and I are just sharing thoughts.
Old 05-30-2020, 06:23 AM
  #46416  
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It has been stated that since the right cylinder is now the left cylinder that the right intake port is now the exhaust port, and the right exhaust port is now the intake port the timing needs to be different, I have no clue about that, I'm OK with the fact it works and works very well. When flipping there is no difference in the feel between the cylinders. When slowly turning the engine with a tiny ball driver in the glow plug hole the left exhaust valve closes well before bdc and the intake valve closes well after bdc, same as the right side.
Old 05-30-2020, 06:42 AM
  #46417  
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Some skinny from Clarence Lee, he did not differentiate between left and right cylinders. The plot thickens.

intake valve opens 50 degrees BTDC
Intake closes 60 degrees ABDC
Exhaust opens 65 degrees BBDC
Exhaust closes 35 degrees ATDC
Overlap========85 degrees
Old 05-30-2020, 06:55 AM
  #46418  
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Still digging, this 1.82 timing.


I hope this readable.
Old 05-30-2020, 07:01 AM
  #46419  
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Well, the cylinders flipped from each other with both intakes on top and both exhaust on bottom so only natural to have two completely different cams. Right cylinder would be normal as in any other saito, intake on the right when facing from the prop, but the other cylinder with the intake on the left would be timed different, the exhaust lobe is the intake lobe, and the intake lobe is now the exhaust lobe. It wouldn't use the same cam since they now open and close at a different relation to the crank.
Old 05-30-2020, 07:15 AM
  #46420  
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Also consider that the cams are spinning opposite directions, so the opening and closing sides of the lobes are reversed as well. I have not seen an actual full camshaft profile yet so there is no guarantee that the opening and closing sides are symmetrical on either lobe.


As far as why the the cams are timed differently between left and right cylinders, even the author states that would be speculation! Well, if it's speculation to him I'll never figure it out!

Last edited by Glowgeek; 05-30-2020 at 07:29 AM.
Old 05-30-2020, 08:28 AM
  #46421  
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Crankshaft splines would do that. What works on one cam, 180* apart may not on the other, but both cams may use the same gear stamp at the factory, so the second notch is added by hand to compensate for the spline difference.
Old 05-30-2020, 02:26 PM
  #46422  
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True, good point acdii.
Old 05-30-2020, 02:56 PM
  #46423  
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Originally Posted by Glowgeek View Post
True, good point acdii.
Lonnie, check this crazy geometry with one cylinder fo

rward of the other.
Old 05-30-2020, 03:31 PM
  #46424  
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Yep, two crank throws on that one and it uses a single camshaft; the one I posted a pic of earlier.

Very nice engine Dave. That Jet bandsaw is pretty handy to have around, huh?

Last edited by Glowgeek; 05-30-2020 at 06:12 PM.
Old 05-31-2020, 02:37 AM
  #46425  
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It looked like this for a few days. Check out the price of these rods: https://www.horizonhobby.com/connect...d%3Ap-sai60t10


The jugs are different construction, as you can see. The left one, on the right is new.

Last edited by Hobbsy; 05-31-2020 at 03:06 AM.

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