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Can't Rotate The Engine By Hand

11K views 29 replies 4 participants last post by  leonmusk 
#1 ·
Hi everyone!
I am new to this forum and I am looking for some advice. I purchased a used MTD Yard Machine, with a 12.5 HP, 28T707-1154-E1 B&G
engine for 175.00. It started right up, but it acted weird. The PO said he replaced the crankshaft and piston rings, but thinks the rings weren't setup correctly. I took the engine apart and the crankshaft looked original and I noticed the gaskets were all original. For sure the PO did not replace anything internal, however while the head was off I saw the counterweight was broken into several pieces. I ordered a new counterweight, which was very difficult to find because B&G no longer makes the part!
I put everything back together, replaced the drive belt with a new one, went to start it and the engine just clicks. It does not turn. I checked the belts and the engine to see if there were any obstacles in the way, but everything looked good. I tried turning the engine with my hand, with the spark plug removed of course and it barely moved. I tried using my socket wrench at the pulley and it was very difficult to rotate the engine. I went at it at the flywheel and as I kept trying to rotate the engine, it started to turn a little easier, but by a certain point during rotation, it gets hard to turn and then it gets easier, then hard, then easier, etc, etc.. Basically, by one full rotation, it gets tight then it's easier to turn, then tight again, which I assume is when the piston is at TDC and compression is formed, but again, the spark plug is out. There shouldn't really be compression. I used assembly lube on the crankshaft journals, rod bearings, cam lobes, and counterweight.
Does anyone know what might be wrong? I made sure the engine was timed and at TDC before putting it back together.

Thanks in advance!
 
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#2 ·
First impression, makes me think the crankshaft endplay is too tight. Briggs sells several thickness gaskets to help achieve the correct endplay. (Crank end play is the amount the crankshaft can move in and out of the engine, generally anywhere from .003" in some cases .030" at the maximum allowed.
62002


However, if it were the endplay causing an issue, i would think you would get the same resistance during all the way around during the 360° rotation.


See if you can grab the crankshaft PTO end or the flywheel and try picking up on it and pushing down see how much or how little movement you get.
Ideally you use a dial indicator set up properly to set it end play.
 
#3 ·
Thanks for the information. I used the same size gasket as the original. I would assume the end play wouldn't change. I should have rotated the crankshaft before I set it on the frame. I do have to say, I didn't feel any play at the crankshaft while moving it around during re-assemble. I'm a bit confused on how the endplay would change if using the same size gasket. Could it be the magnet at the flywheel that would give tension during rotation? This is my first time taking apart a vertical engine. I'm used to car engines, which is helping me get through the tare down and rebuild.
 
#4 ·
Magnet should have no affect.
sometimes you might have to double up on the gaskets, like use a .015 and .005" to get the right clearance to where it will spin.
If this engine is equipped with a stator (alternator) under the flywheel, i would inspect it to be sure it is not broken or the coils aren't jamming up in the magnets.under the flywheel.

if that checks out, i would evenly loosen the sump bolts, try to spin it, loosen some more. etc. see if t gets easier to turn with less pressure coming from the sump.
 
#5 ·
I do have the alternator that is bolted on under the flywheel. I'm still confused on how the crankshaft can bind using the same size gasket. What changes to lose the gap? I didn't know the tighter the sump bolts are, the less gap you have. I have those sump bolts on tight.
 
#6 ·
When setting the crankshaft end float you must start with the thickest (15thou) gasket. If that achieves the recommended float it’s job done. If it’s too tight , add one of the others. If it’s too slack a shim washer is available. From there on, I would strip the engine completely and reassemble checking everything as you go.
Wild card suggestion. Just suppose the previous owner hasn’t fitted oversized rings into a standard bore ?
 
#7 ·
I started up the engine a few times before stripping it down. It ran good except there was gas mixed with oil. I think the only thing wrong with the engine was the carb. Since the PO mentioned replacing the crankshaft with a new one and vaguely mentioning the piston rings, I decided to strip the engine to verify the rings' positioning. Everything looked good except for the counter weight (dog bone). That was in pieces. I do recall trying to move the crankshaft after fitting the head and it wouldn't move.
I honestly don't want to take the engine apart again, let alone remove it from the frame.
Question, should I be able to turn the flywheel with my hand, or does it have to be turned by the flywheel or at the pulley bolts?
Crankshaft end float? Is that the governor/oil pump that rolls on the Cam gear, feeding oil inside the case?

Thanks for your help.
 
#10 ·
That’s what I thought. I recall being able to turn a flywheel by hand. What I don’t understand is, why would the float change if I’m using the same size gasket? I’m new when it comes to working on vertical engines. I don’t understand how the end play can change if I’m using the same size gasket. There’s nothing wrong with the rings. When I pulled the head off, the piston head and lifters were dry and in good shape, which tells me the rings are doing their job and the engine had compression when I rode it a couple of times before opening the engine. From what I saw, the dog bone was broken and the carb wasn’t in good shape.
 
#11 ·
It could even has something to do with the counterweight, i remember reading in a Kawasaki manual (i think for my fe290 i rebuilt) it said that whenever a part that is relative to the crankshaft is changed, that can affect it.. i personally don't see how the changing the counterweight on that could, but the i'm sure the engineers know.

You didn't have any trouble getting the sump back on did you? sometimes you got to wiggle the crankshaft and wiggle it and wiggle it for it to finally seat all the way down.
 
#12 ·
I took apart the engine again and I'm still not sure why it was hard to turn, but after reassembling, it was easy to turn and I had a little end play. I mounted the engine back on the mower, buttoned everything up and it spins perfect this time, but... won't fire up. It tries, but it just won't. I have spark and after trying to turn over the engine several times, the exhaust was hot to the touch.
I removed the muffler to see what's going on in the exhaust side and gas was present. I pulled off the head to look at the piston head to see if there's any oil or gas and it's dry, which tells me the rings are doing their job. I did see quite a bit of black gunk in the exhaust port. Is there a way to clean that section and does anyone know why there is fuel coming from the exhaust? I do have to say, I did reuse the original carb. I do have a new carb.
 
#14 ·
I'm confused. Ignition coil would cause gas to enter the exhaust port? I'm getting spark. I'm also confused about partially sheared flywheel key. How does that interact with fuel in the exhaust port?
Everything else seems fine. I can tell the fuel is getting burned, but just not enough to keep the engine running, but enough for the exhaust to be hot to the touch.
 
#21 ·
Here's what the inside of the exhaust port looks like. I would like to clean it up. View attachment 62030 View attachment 62030
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Seen far worse that are running satisfactorily.
Thought that I’d answered your query re the coil. A business card air gap will be fine and is well within the recommended range which does vary from engine model to engine model but only by a couple of thousandths of an inch. Pulling the coil away from the flywheel as far as it will go might kill the spark but that would need a stack of business cards.
Not covered so far ( as far as I can remember) is valve clearances or even a loose valve seat.
 
#23 ·
I checked for spark and I got spark, but I am not sure the output of the spark is strong enough. The spark plug looks ok. It's not saturated or gunked up. I think I'm going to readjust the magneto. The engine started up fine before I took it apart, with the exception of gas coming out of the exhaust. I concluded the carb was bad. I swapped the carb with a new one and the gas is no longer present in the exhaust. I can't find the small spring that goes on the governor link. I assume the adjusting idle screw adjusts the governor control? I haven't adjusted the screw yet. Could that be the reason why it won't start? Again,
I'm new at this. I don't know the proper procedure. I don't know if I'm supposed to adjust the screw all the way in and slowly unscrew it until the idle is where it supposed to be. I feel as if the plate that is controlled by the idle screw is closed. maybe that's the reason the engine isn't firing? I don't know. I can't find a repair manual that supplies instructions on how to adjust the idle screw and I don't even know if the governor control spring is needed. Any input would be greatly appreciated.
Thanks in advance.
 
#25 ·
Thanks for the link. I made sure the piston was at TDC and the index marks (dots) on the gears matched. I used a business card to adjust the magneto, but I basically followed a youtube video. I didn't pay close attention to the flywheel, I might have made a mistake by not paying attention to the flywheel location when adjusting the magneto.
 
#26 ·
I decided to look at the flywheel to see if it was aligned with the key. Turns out the key was sheared. I ordered a 10 pack from Amazon, aligned the flywheel, tapped in the key and the engine started up. I noticed some smoke coming out of the exhaust. not Blue or white. Looks like normal smoke. I pulled off the exhaust to see if I still had gas seeping out. No gas. I started it up a few times to see if anything would come out of the exhaust like the last time. Nothing, but is the smoke normal? I did read a few years back the smoke is normal, but yo don't see it normally because we are driving the mower. I just want to make sure the little smoke is normal, or maybe it's just remanence from rebuilding.
 
#27 ·
Black smoke tends to indicate over fuelling. / rich mixture. Blueish white, oil burning from either general engine wear or over filling . May be that the sump oil in your motor has become diluted with fuel during all your efforts to get it running. That would also have raised the level. Sniff the dipstick and if there’s any smell of gas it will be worth draining and refilling .
It’s worth noting that the function of the key is to align the flywheel, not to keep it aligned. That is done by the correct torque ( tightness) of the flywheel nut clamping it on the taper of the crank. - refer to the manual , it could be in the region of 160 foot pounds .
 
#29 ·
If you are referring to the light weight spring that wraps round the link , it is to keep the linkage in tension and aids prevention of surge. Running with out it no harm will come. However, if you are referring to the governor spring the motor won’t open up off idle - always assuming that the governor has not been messed with.
 
#30 ·
I'm referring to the light weight long spring that wraps around the governor linkage. I thought I put it in safe keeping, but I can't find it anywhere. Watch it show up when the new one arrives. LOL
The thicker stout spring that resides behind the accelerator cable and connect to the bottom of the governor link is intact. At least I know I can run the mower until the new spring comes in. Interesting... the engine did surge while it was idling. I hope I can cut the grass one time before the new spring comes in. Thank you very much! I appreciate your help..
 
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