My Lawnmower Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter · #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!
 

·
Registered
Joined
·
266 Posts
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.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #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.
 

·
Registered
Joined
·
266 Posts
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.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #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.
 

·
Registered
Joined
·
39 Posts
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.
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 ?
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #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.
 

·
Registered
Joined
·
266 Posts
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.
there is a torque spec on those sump bolts.

End float is the same as end play.


Edit. here it is
SUMPBOLTS.PNG
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #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.
 

·
Registered
Joined
·
266 Posts
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.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #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.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #14 ·
Possibilities. Ignition coil on back to front and or sheared / partially sheared flywheel key ?
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.
 

·
Registered
Joined
·
39 Posts
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.
I was looking for reasons that the fuel was not being ignited. Assuming that your engine has electronic ignition it will spark at the wrong time with An incorrectly fitted coil or sheared key. Unlike a points ignition unit that will loose its spark entirely under those circumstances.
Appreciate that trying to assist from a distance involves a certain amount of guesswork.
 

·
Registered
Joined
·
387 Posts
With the engine currently not running and the carb is still supplying gas, it has to go some where, and that is the exhaust port.
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #17 ·
I was looking for reasons that the fuel was not being ignited. Assuming that your engine has electronic ignition it will spark at the wrong time with An incorrectly fitted coil or sheared key. Unlike a points ignition unit that will loose its spark entirely under those circumstances.
Appreciate that trying to assist from a distance involves a certain amount of guesswork.
Understood. I appreciate everyone's input. I'm new when it comes to small engines, which the past week has been confusing. I completely forgot about ignition timing. The frustration is growing because it started right up before I took it apart. Could it be the magneto is too far or too close to the alternator? Would that affect the spark, or is it black and white, where there's either spark or no spark. I adjusted the magneto using a business card. I can't find my feeler gauges. I made sure timing was correct by having the piston at TDC and the timing marks on the gears aligned. The only thing I can think of is the carb, The carb is original. I have a new carb and I'm going to swap it out today and see if that solves the problem.
Thanks!
 

·
Registered
Joined
·
39 Posts
Understood. I appreciate everyone's input. I'm new when it comes to small engines, which the past week has been confusing. I completely forgot about ignition timing. The frustration is growing because it started right up before I took it apart. Could it be the magneto is too far or too close to the alternator? Would that affect the spark, or is it black and white, where there's either spark or no spark. I adjusted the magneto using a business card. I can't find my feeler gauges. I made sure timing was correct by having the piston at TDC and the timing marks on the gears aligned. The only thing I can think of is the carb, The carb is original. I have a new carb and I'm going to swap it out today and see if that solves the problem.
Thanks!
The size of air gap between the coil armature legs and the flywheel will make a little difference but a business card will be fine . Using conventional steel feeler gauges is a bit tricky as they get stuck to the flywheel magnets. The correct way of doing the job is to turn the flywheel magnets away from the coil , pull the coil away from the flywheel and pinch up it’s securing screws. Then rotate the flywheel to line the magnets up with the armature legs, insert your business card and slacken the screws so that the magnets pull the armature onto the card.Then do up the screws and rotate the flywheel to aid removal of the card - job done!
 

·
Registered
Joined
·
12 Posts
Discussion Starter · #19 ·
The size of air gap between the coil armature legs and the flywheel will make a little difference but a business card will be fine . Using conventional steel feeler gauges is a bit tricky as they get stuck to the flywheel magnets. The correct way of doing the job is to turn the flywheel magnets away from the coil , pull the coil away from the flywheel and pinch up it’s securing screws. Then rotate the flywheel to line the magnets up with the armature legs, insert your business card and slacken the screws so that the magnets pull the armature onto the card.Then do up the screws and rotate the flywheel to aid removal of the card - job done!
If the magneto is not distanced correctly, can that affect the amount of output at the spark plug?
 
1 - 20 of 25 Posts
Top