Hobbsy

My Feedback: (102)

Contrary to what the bore and stroke lead you to believe, the .82 is a torquer. folks tend to get carried away when looking at the bore and stroke to decide if an engine is a revver or a torquer. The valve timing has much more influence over the torque peak @ whatever rpm than does the bore and stroke. It is an oft over looked fact that a short stroke large bore engine has more square inches of piston surface area for the combustion pressure to push on hence offsetting some of the longer strokes advantage.

mike early

But, because it has a shorter stroke, it would be easier to achieve higher revs, we presume?

Hobbsy

My Feedback: (102)

Yes, if the valve timing would permit it.

w8ye

My Feedback: (16)

The Saito 82 has the bore of a Saito 100 but it only has Saito 91 valves.

Apparently, the smaller valves permit more low end torque and possibly they are less shrouded than the 100 valves would be?

retransit

My Feedback: (18)

Doesn't the inertia advantage of the long stroke overcome any advantage of a larger piston area with everything else (including valve timing) being equal? I'm referring to equal displacement engines with different bore and stroke dimensions.

Do you happen to know the torque ratings of the Saitos?

Bob

retransit

My Feedback: (18)

Hobbys,
I have another thought. For a given amount of combustion pressure that charge would be dissipated over a larger piston area as compared to a smaller bore. One would have to increase the amount of charge, as in lengthening the the intake duration, isn't that correct?

Bob

w8ye

My Feedback: (16)

Whatever it is, the Saito 82 has almost as much power as the Saito 91 at less weight and size

Hobbsy

My Feedback: (102)

That inertia advantage of the long stroke can be partly matched (as Jim mentioned) by using smaller valves in the shorter stroke engine so the intake slug will be smaller in diameter and therefore easier to get moving. If using a larger bore to accomodate larger valves, then valve lift and overlap are both increased to aid and abet the inertia of the intake and exhaust lugs. This increases rpm which further increases the intake and exhaust tuning taking more advantage of the inertia of the intake and exhaust pulses(slugs). You have to know what you're doing when you go there. Our engines need to be tractable and predictible rather than out and out powerful.

My brother had three 358 Chevy's with 420, 505 and 555 hp respectively, 420 hp engine was the fastest on a 3/8ths mile track, the 505 was the fastest on a 5/8ths mile track, the 555 hp engine was slower and harder to drive. My brother called the 555 hp engine, 'sledge hammer", like.

japes999

My Feedback: (9)

Cherokee,

You were right, my low RPM was due to me being off by one tooth on the cam gear. Thanks for the instructions on how to do it right - wasn't too hard. I adjusted the valves too with the supplied feeler gauge, and now I'm *****g out at 8550 with a MA K 15x8. The RPM still seems a little low for that prop, does that sounds about right for an older FA-120?

A few questions:

Should you adjust the valves cold or hot?

Now that I have it timed correctly, it seems as though it is a bitfussier, and doesn't repsond well to being richened out at the top end. If you richen it more than 100 or so RPM it gets very unreliable and sputters somewhat, any ideas on that?

After reassembly do you have to start the break in procedure over again, as the piston ring has been moved from the original position? When I took the crankcase cover off today to retime the cam, I noticed the oil in the bottom of the crankcase had a slight metallic appearance to it.

I have an airbleed carb, and the air bleed screw for the low end mixture requires a whole lot of movement, it seems as though whatever I do with it doesn't make much difference. I get a nice low idle, but after waiting 15 seconds or so, the transition to high speed seems a little rich. The pinch test at idle increases RPM nicely, however. Should I leave it alone?

Since it is an airbleed, I have the mid range disc, at what RPMwhat I wnat to pinch test that to set it properly?

Last, I am using an OS type Fplug, and the idle seems stronger and the top end seems a bit more reliable when the glow charger is still apllied. I tried it with 2 new plugs and noticed the same behavior on both of them. Is this normal, or should I be trying a new plug?

Sorry for all the questions, but this is my first 4-stroke, and I'm pretty clueless...

mike early

One time, in one magazine, I saw a Saito powercurve-dynograph plotted out. It was the first Saito 125 review. I've looked and looked for that article again....

I'd like to see a dynograph of every Saito. That would be a help in prop selection with a tach. One could want the RPM to be at max torque, or for different applications, propped at the highest HP. Of course, seat of the pants works just as well, but one has to buy a lot more props that way....

Cherokee Flyer

You need to set the valves cold, I usually set them the day after I have run the engine. I also set them close, 0.0015 as a go guage and 0.002 as no-go, that is just what has worked for me for many years. And yes, you are breaking in a new ring position, did you change the bearings also, if so they will need to seat in.


L.

Craig 01

Model engine ball bearings do not require a "seat in" if installed "fully seated" initially and correctly within the case.

Saito18

My Feedback: (32)

Hello,

Can I join? I own a Saito 65, 72, 82 and 125. All run great!

Thanks.

w8ye

My Feedback: (16)

A re-ringed engine breaks in rather quickly

NM2K

My Feedback: (14)

Equally important is the position/placement of the wrist pin in the piston.



Ed Cregger

FNQFLYER

Reference the above discussions
1/ The little red Saito book put out by RCM all those years ago and still available around the traps will answer all the above questions, and it has beaut diagrams, charts and drawings for specialist tooling to use as required
There is also a little blue book for OS engines and I have a guard dog keeping an eye on my copies

2/ Plugs, here in OZ we have a new all encompassing range of Saito plugs that are great for general sports use and Texaco (Old Timer) flying, find your own for Duration (O/T vertical drag racing)

3/ In Texaco we turn 15 x 8 APC props on 62's and 65"s at around 4 to 5000 rpm for fuel economy and 13 x 6 Bolly props (if you can get them) 40% nitro 20% synthetic oil in the same engine for duration.  For general sport flying 12 or 13 inch props of varying pitch are the go 

w8ye

My Feedback: (16)

Nitro doesn't do anything for fuel economy

mike early

Nitro kills fuel economy. 1.7to1 vs 6.5to1 for methanol.

Hobbsy

My Feedback: (102)

FN, you have a real treasure in your Country, the TAIPAN 4c plug is great, the silver package below. I really like the way the insulators are color coded. Most plugs lose their identity when removed from the package.

Cherokee Flyer

As any bearing is not perfectly aligned when installed, at the first warming of the engine theywill align with the crankshaft. This is the reason precision spindles are run in when they are re-assembled.

L.

Rudolph Hart

I'm still waitin to hear that zero stroke engine joke ed

Craig 01

I would be interested if you would take the time and explain the process of how the front bearing aligns itself with the crankshaft at the first warming of the engine.

frets24

My Feedback: (15)

"As any bearing is not perfectly aligned when installed"

The degree of "mis-alignment" here is virtualy infintesimal, but there is the possibility of it none the less. Unless someone has really just beat the bearing in and not even tried to install it with some degree of precision, it's not something that we really need to give a second thought to, as it is self correcting in the first extended run of the engine in our situation.

When the bearing is pressed over the crank shaft and into the bearing cup in the front end of the case, in all likelihood, the outer race will not be fully seated AND geometricly aligned to the inner race. Likewise for the inner race to the outer and the true line of the crank. Both may be everso slightly "cocked".
Due to manufacturing tolerences and the "less than precision" methods and equipment we have available to us at home it just winds up that way. Whether you press in the bearing or gently tap it in with a mandrel or whatever doesn't matter. Even if you gently tap around the outer race to ensure a full seat, it bounces the opposite side up. same with the inner race. The result is that the two are not aligned. One or probably both are tilted relative to each other, the cup, crankshaft and relative to their optimum plane of operation. Again the degree to which they are off is so small that it would be very difficult to measure without some VERY sensitve and precise setups and tooling.

"at the first warming of the engine they will align with the crankshaft" Assuming that the machining has been done correctly to start with. The bearing can only shift as far as the physical limits of the structure will allow.

When the engine is run up and heats up the very first time after assembly or reassy the combination of the slight loosening of friction fit around the bearing, vibration, drag and resistance on the races and balls along with gyroscopic forces cause the bearing outter race to shift or settle into it's optimum position and "seat"; think of the outter race, balls and retainer ring as being a gyroscope....they are going to want to be aligned to the the rotational force. The inner race will shift more slowly but within the first or second running will be self aligned to it's best position also. The best running position for the outter race may not necessarily be firmly against the step at the bottom of the cup all the way around. The combination of tolerences may have that bearing a few 100,000ths off "on-plane" if firmly seated all around. Running in will correct that. The physics and forces of running it in will take care of the tiny misalignments inherent in the beast.
Have you ever pulled a bearing and found just a wee, tiny bit of goop in a small crecsent, just around one small area of the bearing seat? Did you ever really notice? How about only PART of the number on the face of a bearing transfered to the mating surface?

Anyway, minor, minor stuff and not really worth the time spent pondering it unless you are just one of those who loves to know stuff about stuff just for the sake of knowing about it. (Or you're an engineer/manufacturer/designer and you HAVE to know about it.)

Other than being about as clear as mud, hope it helped...

retransit

My Feedback: (18)

I bet you're really sorry you asked! LOL

Bob

mike early

Maybe someone can find that article with the dynograph of the Saito 125 and scan the chart and post it here. That'd be wonderful....