91AC or 91FZ
#3
My Feedback: (2)
RE: 91AC or 91FZ
The two differences from the outside are:
91AC Small Carb and "old sytle" needle valve (larger end in a "stainless steel" coloring).
91 FZ Standard carb (little larger "throat"), similar to the 110FZ carb and the newer needle valve. Side by side the 91 FZ and 110 FZ will look very close to each other. If this doesn't help post a picture and I can let you know which one your have.
Jimmy Skids
91AC Small Carb and "old sytle" needle valve (larger end in a "stainless steel" coloring).
91 FZ Standard carb (little larger "throat"), similar to the 110FZ carb and the newer needle valve. Side by side the 91 FZ and 110 FZ will look very close to each other. If this doesn't help post a picture and I can let you know which one your have.
Jimmy Skids
#4
Senior Member
RE: 91AC or 91FZ
One thing that can confuse is the older needle assembly and the new style needle assembly can be interchanged. Meaning remove the older one needle and needle seat together and you can replace the engine needle assembly with the newer style one.
The older larger Needle valve is a tell tale sign...but that doesn't solve the problem of the 91AC that somebody swapped out the needle assembly to the newer version.
I did this to all my older 120's as the new assembly is better with wear and vibration over time. Less mass swinging around with the engines vibration.
The carb inlet is larger on the 91FZ but without having both side by side its tougher to tell the difference.
Troy Newman
Team YS
The older larger Needle valve is a tell tale sign...but that doesn't solve the problem of the 91AC that somebody swapped out the needle assembly to the newer version.
I did this to all my older 120's as the new assembly is better with wear and vibration over time. Less mass swinging around with the engines vibration.
The carb inlet is larger on the 91FZ but without having both side by side its tougher to tell the difference.
Troy Newman
Team YS
#5
My Feedback: (2)
RE: 91AC or 91FZ
Troy,
Very true. I've also done the needle swap before on a 120. In fact I know of some that have swapped the carb/throttle body on the 91AC for the updated version. If 42etus does have the old style needle then at least that would make the deduction easier. I'll try to post pictures of the AC and FZ side by side if time allows after work.
Skids
Very true. I've also done the needle swap before on a 120. In fact I know of some that have swapped the carb/throttle body on the 91AC for the updated version. If 42etus does have the old style needle then at least that would make the deduction easier. I'll try to post pictures of the AC and FZ side by side if time allows after work.
Skids
#6
RE: 91AC or 91FZ
I have a 91 AC, in a flight I lost the muffler. I can´t find the original one because they are discontinued. Can I use the muffler of the 91 FZ in the 91 AC without any modification ?
#8
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Join Date: Feb 2008
Location: Salmon Arm, BC, CANADA
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RE: 91AC or 91FZ
I inquired a few years ago about replacing a crankcase on a 91AC with a minor leak at the front. Runs fine but dripped a little occasionally. I was told since the parts were unavailable just run it until it gives out.
Are you indicating that the 91FZ crankcase is a direct replacement for the 91AC and that I could send it in and have it repaired reasonably??
That would change the way I think about the future of the engine.
Are you indicating that the 91FZ crankcase is a direct replacement for the 91AC and that I could send it in and have it repaired reasonably??
That would change the way I think about the future of the engine.
#9
Senior Member
RE: 91AC or 91FZ
I don't know how we got onto a crankcase is the same, from talking about mufflers.
However, I think that a 91FZ crankcase will work on the 91AC. I'm not 100% positive but you can can YS Parts and service and ask them. There may be some other misc parts you might need to convert over to the 91FZ case but I think it might be possible. Richard can tell you the specifics.
you can get their contact info from www.yspartsandservice.com
Troy Newman
Team YS
However, I think that a 91FZ crankcase will work on the 91AC. I'm not 100% positive but you can can YS Parts and service and ask them. There may be some other misc parts you might need to convert over to the 91FZ case but I think it might be possible. Richard can tell you the specifics.
you can get their contact info from www.yspartsandservice.com
Troy Newman
Team YS
#10
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RE: 91AC or 91FZ
ORIGINAL: Troy Newman
I don't know how we got onto a crankcase is the same, from talking about mufflers.
I don't know how we got onto a crankcase is the same, from talking about mufflers.
Direct support forum
Thread starts out
"Since both engines use the same crankcase marked 91AC, is there a visual way to tell the 91AC and the 91FZ engines apart?"
SO I thought I would ask.
I will go away.[]
#11
Senior Member
RE: 91AC or 91FZ
ss40,
It was not my intent to send you away. Rather we tend to get threads going that stray pretty far from the subject at hand. Not that yours was...but the topic at the time was mufflers.
I welcome your questions and I apologize for adding some levity or a little human response to the question. Like in all things the grin on my face as I typed was not transmitted along with the words I wrote.
I'm sorry.
The 91AC and 91FZ cases are different parts number. It is my belief that they are interchangeable. Like I said there may be some misc parts that are needed to convert over to the new style case. YS is very good about using common parts among its engine line. needle valve assemblies, and bearings, carb bodies, and throttle barrels are often items that translate in some way across the different sizes. Backplate assemblies, and regulator parts are also often used on various size engines.
So to answer your question yes there is way to replace the case on your 91AC. however given the price of some of those parts that you may need it might not be in the best $$ and cents sense.
The part numbers for the 91AC and 91FZ that are different that could be attributed to the case.
case $42.95
cranksaft $61.25
so this $100 in parts that are different.
Now lets talk about the crank. I think the biggest change was newer one doesn't use the woodruff key instead is uses the tapered collet like the newer engines. This means you may have to purchase a new drive washer, and the tapered collet also. I don't know if the old crank will still work in the newer case or not.
This is why you need to call YS parts and Service regarding this issue. They can tell you if your 91AC crank will fit into a 91FZ case. If it doesn't then you would have to get a new crank, new drive washer, new collet, and of course new bearings, gaskets, and o-rings. This will easily add up to around $150-200 if you have to do them all. YS parts and service might be able to get some parts and make it work cheaper, but for you to buy the parts nd do it yourself this is what you are looking at. The decision to spend $200 on a engine that is over 10-12years old when a new 110S can be purchased for $360 is a decision that you would have to make for yourself.
To me I would fix it..but then again I know how to make things work, and would only change the parts that would be needed.
The question needs to asked of YS parts and service, will a 91Ac crank fit in a 91FZ case. If it can then you are out just the bearings and the case. The $61 crank and the drive washer and collet kinda blow the repair a little on the high side.
Again I hope this info helps you.
Troy Newman
Team YS
It was not my intent to send you away. Rather we tend to get threads going that stray pretty far from the subject at hand. Not that yours was...but the topic at the time was mufflers.
I welcome your questions and I apologize for adding some levity or a little human response to the question. Like in all things the grin on my face as I typed was not transmitted along with the words I wrote.
I'm sorry.
The 91AC and 91FZ cases are different parts number. It is my belief that they are interchangeable. Like I said there may be some misc parts that are needed to convert over to the new style case. YS is very good about using common parts among its engine line. needle valve assemblies, and bearings, carb bodies, and throttle barrels are often items that translate in some way across the different sizes. Backplate assemblies, and regulator parts are also often used on various size engines.
So to answer your question yes there is way to replace the case on your 91AC. however given the price of some of those parts that you may need it might not be in the best $$ and cents sense.
The part numbers for the 91AC and 91FZ that are different that could be attributed to the case.
case $42.95
cranksaft $61.25
so this $100 in parts that are different.
Now lets talk about the crank. I think the biggest change was newer one doesn't use the woodruff key instead is uses the tapered collet like the newer engines. This means you may have to purchase a new drive washer, and the tapered collet also. I don't know if the old crank will still work in the newer case or not.
This is why you need to call YS parts and Service regarding this issue. They can tell you if your 91AC crank will fit into a 91FZ case. If it doesn't then you would have to get a new crank, new drive washer, new collet, and of course new bearings, gaskets, and o-rings. This will easily add up to around $150-200 if you have to do them all. YS parts and service might be able to get some parts and make it work cheaper, but for you to buy the parts nd do it yourself this is what you are looking at. The decision to spend $200 on a engine that is over 10-12years old when a new 110S can be purchased for $360 is a decision that you would have to make for yourself.
To me I would fix it..but then again I know how to make things work, and would only change the parts that would be needed.
The question needs to asked of YS parts and service, will a 91Ac crank fit in a 91FZ case. If it can then you are out just the bearings and the case. The $61 crank and the drive washer and collet kinda blow the repair a little on the high side.
Again I hope this info helps you.
Troy Newman
Team YS