• June Project of the Month (Click "x" at right to dismiss)
[4]

Small engine shaking too much when running, Why?

[3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#1
I've bought couple of small generator couple of months back and started a thread on this forum, link: https://www.hobby-machinist.com/threads/old-gasoline-generator-repairs.66014/ The smaller one is finished works as it should, but the Tecumseh HS40 powered Bosch is definitely something wrong, now the carb works as it should and the ignition seems to work right, but the entire engine and generator is shaking so much it walks at walking speed on the garage floor. Any advice what would cause so much imbalance in the engine, i've split the generator of the engine is still shaking, the flywheel key and the flywheel are both good, i've change the oil today and run the generator but it started dying after 15 min of running, it will star on the first pull again and run almost seams the fuel is shaking so much in the carb it starves. It is mounted on rubber mounts to the frame which allow it to move a lot, very strange, any advice is much appreciated
DSC_0284.JPG
 

GA Gyro

H-M Supporter - Premium Member
H-M Supporter-Premium Member
Joined
Aug 12, 2014
Messages
930
Likes
203
15
#2
I would start with ignition timing... sounds like it may be just a little too advanced... firing just before TDC... causing pressure on the piston before it crosses TDC... thus the shaking.

OTOH... firing waaaay too late could cause shaking also.

Check ignition timing first... then go looking for anything loose that shakes or rattles...

Might be a magnetic thing in the genset, however given it shakes with the generator removed... probably the engine.
 

mikey

Active User
H-M Supporter-Premium Member
Joined
Dec 20, 2012
Messages
3,902
Likes
4,152
#3
Might also be the mixture on the carb.
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
3,229
Likes
1,534
#4
Is the engine haunting rev up slow down? Try holding the throttle on the carb to see if it's the governor or the springs to control the speed. It should be set at 3600rpm max. Are the isolation mounts on the frame or between the frame and generator ? Most of those will inherently waddle if not locked down. If it's dying at fifteen minutes , inline spark test it running , if no spark when it dies its the ignition , if still sparking Ck the lid on the tank for breather holes. It will hold the fuel if not vented ,. Small jet holes in carb can be blocked or water present also.
 
Last edited:

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#6
Is the engine haunting rev up slow down? Try holding the throttle on the carb to see if it's the governor or the springs to control the speed. It should be set at 3600rpm max. Are the isolation mounts on the frame or between the frame and generator ? Most of those will inherently waddle if not locked down. If it's dying at fifteen minutes , inline spark test it running , if no spark when it dies its the ignition , if still sparking Ck the lid on the tank for breather holes. It will hold the fuel if not vented ,. Small jet holes in carb can be blocked or water present also.
At slower speed seems to be more stable, at high, on which needs to run to achieve 50Hz speeds up and down, i can see the governor opening and closing the throttle, i can open the throttle by hand but as soon the engine speeds up the governor closes the throttle, the engine and generator mounts are soft rubber and when running it shakes about 50 mm in both directions which causes it to walk, the fuel tank has a breather a aslo run it with the fuel cap backed off, i've been in that carb so many times now i know it is clean and all the jets are clean, could the timing be causing this?
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
3,229
Likes
1,534
#7
Ok we're getting somewhere, on the rod or next to it the throttle link should have an extra tiny spring in a separate hole or in with the linkage. Is it missing ? Is it a bowl carburetor ? The bowl nut does it have an adjustment screw n it? Is there a separate low speed jet in the side ? If there's a adjustable jet take the bowl nut out , unscrew the adjustment screw , in the bowl nut there's a tiny hole on an angle just above the lower part of the thread push a wire thru it to clean it. The low speed adjustment screw may be blocked , if you have 2+2 carb cleaner spray it in the holes , you can use air compressor to blow out to help. With it haunting it's usually blockage or the spring to hold tension on the throttle linkage is missing or installed wrong. As for timing the only timing on those is the flywheel key ... If it's half sheared or on backwards it will make for kickbacks when starting or back fire thru intake valve. Tecumseh are fickle but we're great engines really . They all have oil pumps not just slingers for lube distribution.
 

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#8
The small throttle return spring is present and attached right, the carb is a bowl type, The bowl nut has no adjustment screw in it, is solid there is no hole at an angle, i've read all the repair manuals i could find and know exactly what are you talking about, there is an adjustment screw near the throttle lever, the carb is spotlessly clean, infect the entire engine i don't believe it has more than few hours total run time, you can see the points cam is like new, the flywheel key is straight it has some marks but is not damaged, the ignition plate has adjustment and i can hear it misfiring and backfiring when is running not sure is it thru carb or exhaust. The biggest problem now is the violent shaking (vibration),which i think is is making the fuel bowl shake so much is starving for fuel, is there something like contre weight or balance weight that could cause this, when i had the generator motor separated, i clamped the Tecumseh engine to my workbench, all steel very heavy, when i fired it up the vibrations in less then 30 seconds all my wrenches and sockets fell on the ground.
DSC_0282.JPG DSC_0274.JPG
 

tq60

Active Member
Active Member
Joined
Jan 11, 2014
Messages
606
Likes
353
20
#9
Check point gap as it is somewhat critical.

The timing can be different depending on gap.

Also check key to make sure not split.

The magneto gap needs correct setting and a matchbook works well.

Check flywheel for chunks of crud or missing fins.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

FOMOGO

Active User
H-M Supporter-Premium Member
Joined
Sep 2, 2013
Messages
1,718
Likes
1,606
20
#10
The magneto gap needs correct setting and a matchbook works well.
Now all you need, is to find a matchbook. .016-.018 If memory serves. Process of elimination. You'll get it. Mike
 

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#11
Now all you need, is to find a matchbook.
You correct on that one Mike, i need to find a matchbook and light it on fire, for all the time lost and all the aggravation. The points are set correct everything is as per the service manual, i'm starting to think this engine may be faulty from the factory in because of that is seen so little use.
 

juiceclone

Active Member
Active Member
Joined
Oct 24, 2014
Messages
191
Likes
110
15
#12
U might lookup whether this model has a history of imbalance? Also, is there a possibility the flywheel is not the correct one, subbed by a previous owner? Maybe check with manufacturer for part no. That level of shaking requires some real explanation. I see that model Tecumseh has flywheel options with/without ring gear, and ally or composite plastic/ally construction. Fins seem to be "set" in plastic.! Single missing fin could be significant.
 
Last edited:

rgray

Active User
H-M Supporter-Premium Member
Joined
Nov 26, 2012
Messages
969
Likes
484
20
#13
The carbs without adjustable needles for the main jet are sometimes lean. That will cause the engine to surge up and down.
The last big ethanol push here caused a lot of this trouble the carbs are lean as possible in the first place then add 15% ethanol fuel and they are to lean and surge up and down.
Never seen one that would "walk" so I would suspect there is a different imbalance also.
As far as being to lean... I take miniature drills and gauge the main jet hole, then drill to next size and see if the surging is then stopped.
If you go to big they are easy to solder closed and redrill.
There is the argument that the jet hole is an orifice and not simply a hole.... very true and if soldered closed and redrilled it will usually require a larger hole to match the original jetting as the hole ends up longer. You can use a larger drill to keep one end length in check, but the other end is not accessible.
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
3,229
Likes
1,534
#14
Your sealed jet carb isn't adjustable, as others are saying a larger jet hole may help. Your points call for .020 , the only other check is the the valve clearance between the valve and the tappets. There they call for .010 each. You might try the can gas they sell , it's usually two cycle mix but it's high octane and if there's any varnish left it'll clean where you can't. Did you change the condenser along with the points . And did you wipe the contacts after setting.
 
Last edited:

David S

Active User
H-M Supporter-Premium Member
Joined
Nov 18, 2012
Messages
1,240
Likes
983
#15
sure sounds like an imbalance due to something major. It doesn't have a two piece crank that has slipped?

David
 

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#16
Your sealed jet carb isn't adjustable, as others are saying a larger jet hole may help. Your points call for .020 , the only other check is the the valve clearance between the valve and the tappets. There they call for .010 each. You might try the can gas they sell , it's usually two cycle mix but it's high octane and if there's any varnish left it'll clean where you can't. Did you change the condenser along with the points . And did you wipe the contacts after setting.
Here we have 95 octane, 98 octane, 100+ octane, on the pumps, i have 100+ octane fresh fuel in it, the fuel and the fuel tank is clean, the condenser and points are still the same, i did vipe the points after setting them, i don't know if i can upload a video here just to show you how much this little engine is shaking and how much it walks on the floor, only thing i can think to compare it to is rock separating screens at a rock quarry.
 

juiceclone

Active Member
Active Member
Joined
Oct 24, 2014
Messages
191
Likes
110
15
#17
sure sounds like an imbalance due to something major. It doesn't have a two piece crank that has slipped?

David
Hmmm .. never considered the possibility of a split type of crank ...only seen those on single cyl motorcycles. If the crank was not assebled or repaired correctly...or slipped? that would imbalance everything plus wear all bearings.
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
3,229
Likes
1,534
#18
Oh I know they walk , not many will sit still unless there real heavy cast iron. The only thing I do know it should run even, and better when mounted with the generator and frame. Tecumseh engines are real dancers always were till mounted , that style with a cast flywheel have counterweights on the larger motors . It's the flywheel which is bouncing it . With out that it wouldn't be start able.
 

dtsh

H-M Supporter - Sustaining Member
H-M Supporter - Sustaining Member
Joined
Sep 22, 2017
Messages
80
Likes
89
5
#20
That looks perfectly normal to me, just need some rubber pads on the underside to give it some grip to the floor and absorb some of the vibration.. Such a small unit doesn't have enough mass to soak up that much vibration.
 

David S

Active User
H-M Supporter-Premium Member
Joined
Nov 18, 2012
Messages
1,240
Likes
983
#21
I am of the same impression. Especially when it stopped walking around and became stuck. My snow thrower has the 8 hp version and when the speed is just right all the control rods and one panel breaks into resonance with the vibration. Of course the mass of the machine keeps it from "walking".

I think yours looks normal.

David
 

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#22
The generator weighs a lot, the whole unit is close to 40 kg, the bottom of the frame has studs it scrapes the concrete as it moves.
 

David S

Active User
H-M Supporter-Premium Member
Joined
Nov 18, 2012
Messages
1,240
Likes
983
#23
I am not sure if the flywheel on that unit is aluminum or cast iron. I would think perhaps aluminum and the generator rotor would act as the rest of the flywheel, like the blade is on vertical shaft lawnmowers.

David
 

BtoVin83

Active Member
Active Member
Joined
Aug 30, 2017
Messages
123
Likes
126
10
#24
Are you sure the crank isn't bent. Had a mower with a bent crank and didn't seem odd but nothing would stay tight on it finally the gas tank flew off and I thought well that ain't right.
 

rgray

Active User
H-M Supporter-Premium Member
Joined
Nov 26, 2012
Messages
969
Likes
484
20
#26
Are you sure the crank isn't bent. Had a mower with a bent crank and didn't seem odd but nothing would stay tight on it finally the gas tank flew off and I thought well that ain't right.
I'll second that thought. Indicate the crank end and see what you have for runout. Not sure how one of those would get twisted, but could happen I guess. Everyone with a bent lawnmower crank knows exactly why it's bent.
 

yendor

Active User
Active Member
Joined
Dec 11, 2013
Messages
166
Likes
50
10
#27
High Octane fuel in motors that do not require it is a waste of money and sometimes will cause reduced performance and symptoms of running rich due to incomplete burn.

Higher Octane is meant for higher compression motors where the ignition timing is advanced and requires a fuel that actually burns slower so the fuel can be ignited well before TDC and it reaches Max Burn at approx. 2 degrees After TDC.
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
3,229
Likes
1,534
#28
I'd say yes for Tecumseh engines it's normal , it needs rubber isolators on the frame with feet . It'll sit and shake all day long and produce power. Just keep a Ck on the oil at every fill up , or daily if used a lot.
 

GoceKU

Active Member
Active Member
Joined
Jul 14, 2017
Messages
476
Likes
798
#29
The frame of this generator has steel feet at the bottom of the frame, which leave deep scratches as it moves around, i'm very surprised so many of you think is normal, because the shaking is so bad i can't keep the extension cord plugged in the socket on the generator, i've used tape even that failed, i'm sure the phone with which i filmed it can't show it as in real life. I do drive diesels, not even the old mechanical diesels shake so much.
 

rgray

Active User
H-M Supporter-Premium Member
Joined
Nov 26, 2012
Messages
969
Likes
484
20
#30
High Octane fuel in motors that do not require it is a waste of money and sometimes will cause reduced performance and symptoms of running rich due to incomplete burn.

Higher Octane is meant for higher compression motors where the ignition timing is advanced and requires a fuel that actually burns slower so the fuel can be ignited well before TDC and it reaches Max Burn at approx. 2 degrees After TDC.

I couldn't have said it better. This is so misunderstood most people think it's the opposite.
 
[6]
[5] [7]
Top