Green Tractor Talk banner

1 - 10 of 10 Posts

·
Registered
Joined
·
61 Posts
Discussion Starter #1
Posting here on behalf of my brother with a dead LT155..

Story as I've understood it

1) was recently serviced and running fine
2) his son was mowing with it, stopped and turned it off to go do something, everything normal to this point
3) Went back out to start it, and reports a "loud rattle" but no start, engine cranking OK

His diagnostic steps so far

1) checked spark at spark plug by grounding to engine.. There is spark
2) Tried starting with starting fluid.. nothing..
3) replaced some crank key that apparently affects timing?

Now, he says with thumb over spark plug hole there's no obvious air movement, which might indicate low compression, or that there's no piston moving, but it seems like something so dramatic as a broken con-rod, crank etc, would make a terrible racket when turning over..

Doesn't seem to be a fuel problem since he's tried starting fluid.

His next step is to remove the head and inspect for damaged valves/piston etc... Any other diagnosis he can try before that?
 

·
Super Moderator
Joined
·
2,698 Posts
The loud rattle noise he reported is an indication of something internal, or at least, something just not right. I'm betting a broken rod. Does it crank really fast? With low or no compression, it's something internal.
 

·
Registered
Joined
·
61 Posts
Discussion Starter #3
Claims it's cranking normal, and no unusual noises (the "rattle" was reported by his 11 year old son, not something he heard)
 

·
Registered
Joined
·
3,228 Posts
You know how kids are. The slight rattle could have been a loud bang. Lol
 

·
Registered
Joined
·
2,843 Posts
Might be a valve hung open or dropped. Or, you lost timing between valvetrain and crankshaft.
 

·
Registered
Joined
·
61 Posts
Discussion Starter #6
Or, you lost timing between valvetrain and crankshaft.
This really seems the most likely to me..

Sounds like it's time for a tear down. Was just wondering if there was some possible sensor or electrical connection that could throw it off..
 

·
Registered
Joined
·
2,843 Posts
This really seems the most likely to me..

Sounds like it's time for a tear down. Was just wondering if there was some possible sensor or electrical connection that could throw it off..
Are you sure you have no vacuum or compression at the spark plug hole?
 

·
Registered
Joined
·
61 Posts
Discussion Starter #8
Not at all, he just said he didn't feel much air movement with thumb over it.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
2,843 Posts
Not at all, he just said he didn't feel much air movement with thumb over it.


Sent from my iPhone using Tapatalk

I had a buddy 30 years ago who used a carved up wine cork just for testing this, push it in and crank and if it pops out she's fine. This was back before we could afford real compression testing equipment.

You could stick a drink straw in the cylinder to see if the piston is fully stroking.
 

·
Registered
Joined
·
61 Posts
Discussion Starter #10
Latest update
Head is off along with flywheel. When I was turning over the motor using the puller for the flywheel, the piston didn’t turn with any frequency. Once in a while, the turn would get tight and it would go back up. Seems like it is an issue with the crankshaft. Perhaps a bearing is failing and preventing the crank from moving correctly? It certainly does not seem right.
I'm guessing broken connecting rod, but wouldn't rule out a sheared, or badly damage crank..
 
1 - 10 of 10 Posts
Top