Craftsman DT4000
Briggs & Stratton Intek 24 HP Model 445677- 0413-E4
TL/DR: After misdiagnosis of an internal engine rattle, I removed engine and opened crankcase to find nothing wrong inside. Motor has 600 hours. Has had regular oil and filter changes and air cleaner service. Has good compression, doesn’t smoke, foul plugs, or use excessive oil. Before I reassemble and install, what parts should I replace as a precautionary measure to ensure long engine life.
The long story…
In the past, I have had trouble with it not wanting to turn over but I could always get it to start by hand rotating it past TDC on the compression stroke and it would fire right up. I assumed it was a weak battery and just kept using it.
One day it suddenly lost power and would barely run over idle. It would backfire when the throttle was open like an exhaust restriction. I removed valve covers to see if valves were opening and found on the left (from back of engine) side the pushrod had fallen out completely. When I removed the pushrod I found it was bent.
Read on this forum somewhere that this is a common problem due to valve guide migration, so I inspected the head and saw the exhaust guide seemed to be extending further above the head and ordered a new head and pushrods.
Replaced all, adjusted everything, cleaned excess dirt and debris from cooling fins, and test drove. Everything seemed fine. Next time mowing, about an hour into the mow, again lost power and backfiring. Pulled valve cover and pushrod is still in place but very loose. Adjuster and lock nut still tight so assumed I had done something wrong and readjusted valve. Test drive, runs fine.
Next use, it ran fine for about an hour. I stopped to empty bags and left motor at idle. The first time I notice that it seems to stumble and stall when I open throttle. I open throttle slowly to full throttle and continue to mow. The next stop, I again leave motor at idle. When I start to open throttle, motor begins to stall as before and won’t take fuel. I continue to slowly open throttle. Suddenly something in engine starts to tick and rattle loudly so I shut it off. Pulled valve cover, valves and pushrods are in place. Try to rotate crankshaft clockwise by hand and motor locks up. Will go counter clockwise but clockwise only moves a few degrees clockwise and locks.
Assuming some internal problem possibly related to compression release I pull motor and open crankcase. I’m really surprised that there is nothing obviously amiss and there is no metal debris in crank case. I’m a little stunned, but needless to say happy there is not internal crankcase damage. I’m even more surprised to find that my engine does not have a compression release. I check the cam lobes and tappets and the internal governor parts. Everything seems to be working. Now I try rotating the crankshaft by hand to see what is locking up. Everything seems fine except for an apparent and consistent tight spot in the rotation when left piston is at TDC. There is no damage to the rod and both rods are securely fastened to crankshaft.
I pull the left side head. I find two small pieces of what I determine was a small screw. There are small impressions in the piston and cylinder head from this debris. In one spot on the piston I can clearly see that the screw was a small screw and very similar to the type used to secure butterfly valves in a carburetor. There is no apparent damage to the cylinder walls, nor are there holes or cracks in the piston or cylinder head.
I grab the carburetor and look down into the intake and I can see the choke butterfly is lying there loose. Both screws are missing. As you can probably guess, by now I’m really pissed at myself for jumping to an erroneous conclusion again, but at this stage of my life I’m getting used to it so I get over it pretty quickly.
I can still see the marks left from the cylinder hone when the engine was first assembled in both cylinders. The cam lobes look fine and don’t appear to be worn, although I have not checked them with a micrometer.
Now I have to reassemble and reinstall everything so I get to the point of this post:
As long as I have it down this far what should I replace? I don’t mind putting in a new cam and tappets, governor, and oil pump or anything else if the experts here think it is advisable.
Thanks for being here and reading this!
Briggs & Stratton Intek 24 HP Model 445677- 0413-E4
TL/DR: After misdiagnosis of an internal engine rattle, I removed engine and opened crankcase to find nothing wrong inside. Motor has 600 hours. Has had regular oil and filter changes and air cleaner service. Has good compression, doesn’t smoke, foul plugs, or use excessive oil. Before I reassemble and install, what parts should I replace as a precautionary measure to ensure long engine life.
The long story…
In the past, I have had trouble with it not wanting to turn over but I could always get it to start by hand rotating it past TDC on the compression stroke and it would fire right up. I assumed it was a weak battery and just kept using it.
One day it suddenly lost power and would barely run over idle. It would backfire when the throttle was open like an exhaust restriction. I removed valve covers to see if valves were opening and found on the left (from back of engine) side the pushrod had fallen out completely. When I removed the pushrod I found it was bent.
Read on this forum somewhere that this is a common problem due to valve guide migration, so I inspected the head and saw the exhaust guide seemed to be extending further above the head and ordered a new head and pushrods.
Replaced all, adjusted everything, cleaned excess dirt and debris from cooling fins, and test drove. Everything seemed fine. Next time mowing, about an hour into the mow, again lost power and backfiring. Pulled valve cover and pushrod is still in place but very loose. Adjuster and lock nut still tight so assumed I had done something wrong and readjusted valve. Test drive, runs fine.
Next use, it ran fine for about an hour. I stopped to empty bags and left motor at idle. The first time I notice that it seems to stumble and stall when I open throttle. I open throttle slowly to full throttle and continue to mow. The next stop, I again leave motor at idle. When I start to open throttle, motor begins to stall as before and won’t take fuel. I continue to slowly open throttle. Suddenly something in engine starts to tick and rattle loudly so I shut it off. Pulled valve cover, valves and pushrods are in place. Try to rotate crankshaft clockwise by hand and motor locks up. Will go counter clockwise but clockwise only moves a few degrees clockwise and locks.
Assuming some internal problem possibly related to compression release I pull motor and open crankcase. I’m really surprised that there is nothing obviously amiss and there is no metal debris in crank case. I’m a little stunned, but needless to say happy there is not internal crankcase damage. I’m even more surprised to find that my engine does not have a compression release. I check the cam lobes and tappets and the internal governor parts. Everything seems to be working. Now I try rotating the crankshaft by hand to see what is locking up. Everything seems fine except for an apparent and consistent tight spot in the rotation when left piston is at TDC. There is no damage to the rod and both rods are securely fastened to crankshaft.
I pull the left side head. I find two small pieces of what I determine was a small screw. There are small impressions in the piston and cylinder head from this debris. In one spot on the piston I can clearly see that the screw was a small screw and very similar to the type used to secure butterfly valves in a carburetor. There is no apparent damage to the cylinder walls, nor are there holes or cracks in the piston or cylinder head.
I grab the carburetor and look down into the intake and I can see the choke butterfly is lying there loose. Both screws are missing. As you can probably guess, by now I’m really pissed at myself for jumping to an erroneous conclusion again, but at this stage of my life I’m getting used to it so I get over it pretty quickly.
I can still see the marks left from the cylinder hone when the engine was first assembled in both cylinders. The cam lobes look fine and don’t appear to be worn, although I have not checked them with a micrometer.
Now I have to reassemble and reinstall everything so I get to the point of this post:
As long as I have it down this far what should I replace? I don’t mind putting in a new cam and tappets, governor, and oil pump or anything else if the experts here think it is advisable.
Thanks for being here and reading this!