Author Topic: LA 46 balancing (Read 13153 times)

Phil Coopy · « **on:** October 30, 2009, 07:26:03 PM »

Talked to someone (forgive the name fade) at Huntersville about better crank balanceing on the LA 46 and it was suggested that substituting an FP 40 crank will help the problem. Anyone have information on this approach?

Phil

Greg L Bahrman · « **Reply #1 on:** October 30, 2009, 08:01:50 PM »

I didn't know there was a problem......What is it

Phil Coopy · « **Reply #2 on:** October 31, 2009, 07:26:31 AM »

Greg,

The 46 vibrates much more than the 40, and I suspect that since they both have the same crankshaft (and counter balance), but the 46 has a heavier piston, it could benefit from better balance. I was going to experiment by drilling the counter balance and pressing in some tungston slugs as we did in my engine shop days, but a fellow I met at Humtersville last week told me that using a FP 40 crankshaft will go a long way towards correcting the balance. I'm asking if anyone else has tried this method.

Phil

john e. holliday · « **Reply #3 on:** October 31, 2009, 09:13:47 AM »

I have not noticed any vibration with my LA 46. Have fun, DOC Holliday

John Tate · « **Reply #4 on:** November 02, 2009, 07:19:07 AM »

Phil,
I am the guy you talked to at Huntersville. I had a vibration problem a few years ago in one of my LA 46 engines. I changed the LA 46 crankshaft with a Tower 40 crankshaft. The problem went away. The Tower 40 crankshaft has a better counterbalance than the LA 46. Now that there are no new Tower crankshafts around, I drill out a 3/16” hole in the counterbalance section of the LA 46 crank with a carbide drill bit and install a piece of tungsten in the hole. I also grind-off some material in front of the connecting rod journal as well. I know this is not perfect but the engine now runs with less vibration. Check out the link to my club’s web site to see how I modify the LA 46 crankshaft: http://control-line.tripod.com/

John Tate
Norfolk Aeromodelers

phil c · « **Reply #5 on:** November 04, 2009, 06:55:57 PM »

Phil, just about every single cylinder model engine needs more counterbalance weight. The counterbalance should be about half the weight of the piston and rod assembly. That is just about impossible to do on a plain steel crank, although the hi zoot crank shown of the Norfolk site might be getting close if it's used with an ABC or ceramic p/l . You can never get rid of the vibration, but the right counterweight on the cranks spreads the vibration out in all directions so you won't see the nose on a profile shaking so badly when the motor hits that particular resonant rpm.

Mark Scarborough · « **Reply #6 on:** November 04, 2009, 10:17:40 PM »

sheesh, there are a TON of LA 46 s flying around the northwest, I have never seen anyone complain about vibration on them,, profiles or otherwise. what is the rest of your combo? fuel, prop, rpm, ect,, maybe thats where the issue is,, Heck I thought my LA 46 was smoother than my FP 40s!

John Tate · « **Reply #7 on:** November 05, 2009, 07:24:12 AM »

Mark.
I had an airplane with flimsy landing gear with wheel pants. The airplane was flown with an OS FP 40 for a long time with no problem. Later I changed the 40 out with an LA 46. You could hear the wheel vibrating around hitting the wheel pants. The vibration also caused engine run problems. When I went back to the FP 40 the problem went away. After balancing the LA 46, there were not problems relating to vibration.

John Tate

Alan Hahn · « **Reply #8 on:** November 05, 2009, 07:54:56 AM »

My guess is that "excess" vibration is often a big function of the airframe--particularly the fuselage.

If you hit the resonant frequency of the fuselage with your setup, then even a nominally ok engine will have problems. If then you try to lower the vibration on that engine, maybe you can get the vibration low enough so that normal dampening of the wood will solve the problem.

So I think that everyone can be right on this topic.

Mark Scarborough · « **Reply #9 on:** November 05, 2009, 09:51:24 AM »

alan, agreed, there are true and not true situations everywhere surrounding this.
Resonance is a huge deal, it can be changed by altering the mass of the nose, the mass of the prop, the rpm the engine runs in , all kinds of things,, thats one reason I asked what his setup was, just to get a feel for comparativly what he was doing.

Personaly, my LA are very smooth, but I do NOT run them low rpm, they all run with a nominally 4 pitch prop in the 9600 to 10000 rpm range, mostly a 12.25 x 3.75 APC

Alan Hahn · « **Reply #10 on:** November 05, 2009, 10:44:30 AM »

Mark,
Yes I know what you are saying, and I know what John is saying.

And the difficult part is trying to understand what other people are reading into everyone's comments.

For example if someone makes a comment on --lets say---their electric power setup that works well but costs a zillion $$$. I want to immediately comment that you can also get one much cheaper. However the original poster is correctly describing their own system, and may not even be claiming you need to spend a zillion bucks---but that's not usually how I see it, and I feel it is my duty to post a alternative. Probably explains a lot of my posts!

But anyway, I also have 2 LA 46's and they seem to be fantastic engines. I tend to run them in a deep 4 stroke, and they just grunt.

What I am saying is that sometimes we all run into specific situations that require solutions to the problem. However that solution isn't necessary for everyone--but that is hard to figure out on forums like this.

Maybe this falls under "Different Strokes for different Folks" --sort of pun intended!

Phil Coopy · « **Reply #11 on:** November 05, 2009, 08:44:33 PM »

Not to stretch this into some kind of argument, but what started me thinking about this was that I changed from an LA40 to an LA46 on both my Vector 40 and my Gee Bee sportster, and noticed more vibration on both of them. Did all the prop balance etc. So I looked at the balance situation for both LA versions. The counterbalance on both are the same but the piston is heavier on the 46. That can't be right. So I did the weight an measure procedure (as I have been doing for years in engine shops on single and multiple cylinder performance and aircraft engines), and when I made up the proper bob weight for the piston rod combination it turns out that the engine is way underbalanced. As soon as I get a chance I'm going to put some tungsten slugs in one of the cranks to balance it at 50% (the usual starting point) and see what happens. It may seem trivial but an out of balance single cylinder engine loses a lot of power. If anyone is interested in the numbers when I finish I'll be happy to supply the technical info.

Phil

John Tate · « **Reply #12 on:** November 06, 2009, 11:50:33 AM »

Phil.
I made a weight that was 52% of the weight of the connecting rod and piston. Then placed the weight on the connecting rod journal of the crankshaft. Then balanced the crankshaft as close as I could. The 3/16” diameter tungsten installed came out close. I cannot remember where I found the info on the 52% of the weight of the connecting rod and the piston part. Sign of old age I guess.

John Tate

Bob Reeves · « **Reply #13 on:** November 06, 2009, 12:37:00 PM »

Quote from: Alan Hahn on November 05, 2009, 10:44:30 AM

Mark,
Yes I know what you are saying, and I know what John is saying.

And the difficult part is trying to understand what other people are reading into everyone's comments.

For example if someone makes a comment on --lets say---their electric power setup that works well but costs a zillion $$$. I want to immediately comment that you can also get one much cheaper. However the original poster is correctly describing their own system, and may not even be claiming you need to spend a zillion bucks---but that's not usually how I see it, and I feel it is my duty to post a alternative. Probably explains a lot of my posts!

But anyway, I also have 2 LA 46's and they seem to be fantastic engines. I tend to run them in a deep 4 stroke, and they just grunt.

What I am saying is that sometimes we all run into specific situations that require solutions to the problem. However that solution isn't necessary for everyone--but that is hard to figure out on forums like this.

Maybe this falls under "Different Strokes for different Folks" --sort of pun intended!

I think another variable is "what's good enough" some of us are not happy with anything less than the best it can be and others are (rightfully so) content with good enough. Neither is wrong and both have to do and use what works for them but what works for one isn't sometimes good enough for the other.

Phil Coopy · « **Reply #14 on:** November 06, 2009, 03:49:47 PM »

Bob,

And some of us retired guys just got too much time on our hands.

Phil

proparc · « **Reply #15 on:** November 06, 2009, 10:13:41 PM »

This business of engine balancing is always one that I personally have been very interested in, and wished that I could do. Don't you have to take into account the weight of the wrist pin also?
Please continue with this thread and any info or pictures you may have on the process.
I am not aware of any full size high performance engine that isn't VERY carefully balanced to say the least.

You guys have a really neat skill.

Greg L Bahrman · « **Reply #16 on:** November 06, 2009, 10:23:41 PM »

Milton,
If you go to reply no. 4 and click on the link at the bottom of the text there is some nice pictures of the crank balance and some updates for the LA46. Good information you will like it.

John Tate · « **Reply #17 on:** November 06, 2009, 10:30:00 PM »

Proparc.
You are correct with the weight of the wrist pin. When I listed the connecting rod and piston earlier, I should have included the wrist pin as well.

John Tate

Phil Coopy · « **Reply #18 on:** November 07, 2009, 09:36:48 AM »

Here is the process: (Taken from the PMB Model Boats site)

Firstly, any material that you can remove to reduce the reciprocating mass( piston/wristpin/ring/top half of rod) will make an improvement in engine performance, maybe not noticeable at lower rpm's but certainly at high rpm's plus it reduces stress on the engine parts. This will affect the balance of the engine but not greatly. However , it is a fact is that it is IMPOSSIBLE to balance a single-cylinder engine. The best that can be done is a compromise. The crankshaft counterweights will partly balance the reciprocating mass (piston/ring/wristpin/top half of rod). but this will introduce an out of balance at 90 degrees to the line of the cylinder but we have to put up with that. Simply put, to balance a single cylinder engine to the best compromise, do this if you have LOTS of time.
Use a good quality scales, digital if possible. Take apart the crank assembly, weigh the bottom half of the rod and then the top half of the rod. Then weigh the piston/ring/clips/wristpin as one assembly. Add the weight of the top half of the rod to the weight of piston/ring/clips/wristpin. Now you need to take a percentage of this weight of between 50 to 60%. Lets say we use 55%.
Add this 55% to the weight of the bottom of the rod and machine a piece of brass or steel of this weight to fit over the crankpin. Reassemble the crank with this weight in place and balance the crank on the ballrace surfaces on 2 knife edges. If the crank rotates because its heavier one side than the other( which it will do) you must grind metal off the heavy part of the crank-webs around the crankpin area or wherever until it does balance. At this point you will have balanced the engine to a balance factor of 55%. This balance factor will vary from engine to engine and is rpm dependent to a certain extent but at 15,000 rpm a factor of 55% is not too far off.

(At our lower rpm's, closer to 50% seems to work better, but that's hearsay and I have not tested that. It may be because of the imbalance cause by the chunk that is machined out of the crankshaft for the intake port.)

Phil

Ward Van Duzer · « **Reply #19 on:** November 07, 2009, 12:03:40 PM »

There are lots of ways to help bring our engines into better balance as I learned when I worked for Randy. But I am surprised that no one on this post mentioned the cheapest and simplest of all balancing techniques. As old as Fox .35's them selves.

Loosen the prop and rotate it 180 Degrees. Done!

or

Try a three bladed prop. Somehow an odd number of blades helps to smooth thins out! Done!

Ward - Older than Fox .35'S

Motorman · « **Reply #20 on:** October 08, 2024, 06:35:05 PM »

I see there are 2 different cranks for the LA 46. One is forged and one is cut from billet. Just wanted to know if one has more counter weight than the other.

Thanks,
MM

john e. holliday · « **Reply #21 on:** October 09, 2024, 09:17:02 AM »

Wards solution is what I was always told.

Ken Culbertson · « **Reply #22 on:** October 09, 2024, 11:54:02 AM »

Quote from: john e. holliday on October 09, 2024, 09:17:02 AM

Wards solution is what I was always told.

In my early years it was hard to find a McCoy or Fox that was in balance and I was too young to be tearing them apart. I was told that the answer to an out of balance motor was an out of balance prop. I also had a couple of prop washers with off center holes.

Ken

Colin McRae · « **Reply #23 on:** October 09, 2024, 05:33:06 PM »

I have both stock 46 and 40 LA engines. I have not noticed any undue vibration issues with either engine.

Might it possibly be a resonance issue with the model itself? Or the engine is not solidly mounted? I did have a 25LA on a CG Shoestring w/ a properly balanced prop. The model vibrated quite a bit at around 11,000 rpm. But at 12,000 rpm, no undue vibration. So, I chalked it up to a model / engine combination issue and resonance occurring at around 11,000 rpm. The exact same engine and prop on a Brodak Shark 402 had no undue vibration at any rpm.

Geoff Goodworth · « **Reply #24 on:** October 10, 2024, 12:26:04 AM »

G'day guys

Here is the full set of pics showing the modes to the LA 46 as mentioned above.

I think there are a couple of pics more providing detail and they are all bundled into a second PDF file.

If I remember correctly, Pat Johnston was the one who originally published the pics.

My LA 46s performed perfectly well straight out of the box and set up as noted in the pinned discussion at the beginning of the topic.

Ken Culbertson · « **Reply #25 on:** October 10, 2024, 07:42:30 AM »

I may be a bit uninformed but why was there an LA40 or LA46? Which one came first. Some class event displacement issue perhaps?

Ken

Lauri Malila · « **Reply #26 on:** October 10, 2024, 09:58:57 AM »

Quote from: Ken Culbertson on October 10, 2024, 07:42:30 AM

I may be a bit uninformed but why was there an LA40 or LA46? Which one came first. Some class event displacement issue perhaps?

Ken

I don't know for sure, but I'd guess that .40 came first. Then they saw a business opportunity in boring it out a little to make it a .46, it would make it useful in a wider range of models. They are not made for any specific class, just for RC-fun.
But as a consequence, increasing the bore seems to be a good way to make good stunt engines. Increasing the cylinder o.d. also makes the bypasses smaller, and that seems to be beneficial for scavenging in our use. Exactly the same story with ST .40 & 46. and many other engines. L

Motorman · « **Reply #27 on:** October 10, 2024, 02:31:14 PM »

Which works better the forged crank or the billet crank? I have a chance to get either one.

MM

Allen Eshleman · « **Reply #28 on:** October 14, 2024, 01:03:44 PM »

Is this what Randy Smith did to his balanced and blue printed LA-46's. I have one and it runs super.

M Spencer · « **Reply #29 on:** October 14, 2024, 07:24:45 PM »

Der Cranks ;

So deers free offem .

https://stunthanger.com/smf/engine-set-up-tips/cranks-a-lot!/msg656575/#msg656575

I threw a fully machined one in a LA , for kicks .

Appears to close 5 Deg. earlier . same open . ( Crank intake timeing ) I dunno if thats a good idea .
With the FP clones , the 44 will swing a inch extra prop . After that the 40 seems gutless . Theres similarities to VF liners & the LA 46 . And the SF has the same
Dimn.s port to flange , but is 22 bore . A SF will haul a ton of aeroplane on a 9 m.m. intake , 12 x 6 , 15 % Nitro . Match a S Tigre 60 zactly ..

Where a LA WONT . !

Thats the clone Sf on a 12 x 6 windsor wood & 15 % Nitro . 4 clicks lean . as they ( ST & SF ) need 6 1/2 Oz and its only got six . AND it dont weigh less than 80 onces . Dry .

We might need two LA 46s to do that .

Dave Hull · « **Reply #30 on:** October 14, 2024, 10:59:33 PM »

Hey! I thought I recognized the thumb in that picture....

This issue came up (for me) when I was working on a friend's engine and noticed a different crank. Some time later, I was trying to get the vibration out of the "very much stock" Cardinal kit-designed nose. The simplest answer at the time was to simply replace the .46LA with a .40LA resulting in noticeably less vibration. The OS parts lists show the same crank part number for both the .40LA and .46LA, but obviously that changed over time. I think the earlier cranks likely have much more counterbalance, but I didn't make measurements.

Dan McEntee · « **Reply #31 on:** October 15, 2024, 11:04:02 AM »

Quote from: Dave Hull on October 14, 2024, 10:59:33 PM

Hey! I thought I recognized the thumb in that picture....

This issue came up (for me) when I was working on a friend's engine and noticed a different crank. Some time later, I was trying to get the vibration out of the "very much stock" Cardinal kit-designed nose. The simplest answer at the time was to simply replace the .46LA with a .40LA resulting in noticeably less vibration. The OS parts lists show the same crank part number for both the .40LA and .46LA, but obviously that changed over time. I think the earlier cranks likely have much more counterbalance, but I didn't make measurements.

I think FP.40 and maybe FP.35 cranks are supposed to be the same also. I would have to search the forum archives but when I wanted to buildup some LA.46s using Brian Gardner ABC P&L parts, and I was advised that I could LA.40 and FP-40 cranks shafts, and checking the part numbers all agreed. I found crank cases and other part sat R/C PartsJapan but they had no crankshafts. So far I haven't noticed any issues. I have a ARF Nobler that no matter what engine I put in it, it vibrates more than I think it should and I have done all the tricks in the books. Sometimes, it's the airplane that is the offender.
Type at you later,
Dan McEntee

Motorman · « **Reply #32 on:** October 15, 2024, 04:13:56 PM »

Quote from: Dave Hull on October 14, 2024, 10:59:33 PM

I think the earlier cranks likely have much more counterbalance.

Which one was the earlier crank?

realSteveSmith · « **Reply #33 on:** October 15, 2024, 07:24:49 PM »

Quote from: Motorman on October 15, 2024, 04:13:56 PM

Which one was the earlier crank?

In this picture, the newest OS crank is on the left, Tower 40 in the middle and older OS crank on the right.

M Spencer · « **Reply #34 on:** October 17, 2024, 07:12:39 PM »

" .Which one was the earlier crank? "

The one in the irst motor !

Id thought the Fuly Cutaway job was the old Iron Piston FP ( 40 & 35 ) crank .

The less expensively machined , the ABC ( nickle ) FP & Early LA crank , and the rough forged the later LA 40 & 46 crank .

Incidently , the FP 35 and 40 are the same - bar the head & bore - so the bits swap out . as in 35 in 40 case or V.c.V. ,

So ALLthe cranks , 35 - 40 - & 46 can be swapped . Dunno on LA to FP with the liners , somebody said something once .

M Spencer · « **Reply #35 on:** October 17, 2024, 07:21:25 PM »

This is gotta 40 FP crank in it .

https://sceptreflight.com/Model%20Engine%20Tests/OS%20Max%2040FP.html

realSteveSmith · « **Reply #36 on:** October 17, 2024, 08:52:33 PM »

Quote from: Scientifiction . on October 17, 2024, 07:12:39 PM

...Id thought the Fuly Cutaway job was the old Iron Piston FP ( 40 & 35 ) crank...

This is the crank out of a Tower 40. I don't have any iron piston FPs but the article you linked above does show a crank that looks similar to this Tower 40 crank. I wasn't in a position (read that as 'I was too lazy') to measure the timing on this.