A friend called yesterday and his 3 year old, John Deere 19.5 HP, single cylinder riding mower suddenly lost power, sputtered and wheezed to a full stop. Would crank but not start so I stopped by to look and see what it might be. I pulled the OHV cover to look at the rocker arms and the exhaust worked fine but the intake didn't move at all since the rocker arm was dangling and completely off the push rod. Re-installed it and the intake wouldn't move either by hand turning, or by starter with plug out. No bent or broken rocker arms or push rods. Both valves appear to open and seat properly but had to manually depress the intake valve against spring pressure, but appeared ok. I haven't dis-assembled it yet, but pulled the engine and took it home. She's waiting to hit the bench for repair as soon as I drain the oil. I suspect it's a broken camshaft. Any ideas? Will post updates as I proceed.
Model# 31P6770140B1
Serial# 081010ZE03140
#2
pugaltitude
Cam lobe sounds as though its worn away so yes a new cam required.
Thanks for the input. You'd think that it would lose power gradually with the camshaft lobe wearing down a little at a time. With no movement at all on the intake pushrod, I thought the cam might have broken clean in two pieces or maybe a lobe worn off? My cousin bought a brand new mower from Home Depot last year, used it for about 2 or 3 mowings and it started clanging and banging like a mule kicking in a tin stall. What it turned out to be was the camshaft broken clean in two pieces, but still enough grabbing to let it run. I don't see how it even ran, but it did!
My Intek 24 wore away the exhaust lobe to a circle due to a pushed guide. When it stopped the "lift" was about .060" to 1/8", enough to get a compression check, but not enough finally to charge the combustion chamber so it could fire. The thing would still mow and was not noticeable until it stopped (Vtwin). Torque rules I guess. In all cases of this reported here it is always by year 2-3. Hmmm.. Infant mortality?
#5
pugaltitude
I had one with engine difficult to start where sometimes it would or wouldnt.
Also engine sounded as though it was misfiring.
The cam lobe had rounded right off.
pugalitude, What is your take on the reason for cam wear? In my case there was severe "stack-up" of the valve train when the guide would not allow the valve to open fully so the "chilled" lifter being much harder , wore away the cam. I could not even measure any wear on the mushroom head of the exhaust lifter compared to the intake lifter which was unaffected. I believe that cast cams are flame hardenable , so perhaps the cooling bath was wrong or? If there is not a load- up problem it is normal pressure of the valve spring which wears the cam lobe?? These little springs do not really exert much pressure.
I just remembered the ASE data and auto mechanics caveats. They never ruled out cam wear on passenger car engines, not pro fuel funny cars etc, so maybe the cam lobes are a recurring process problem?
The problem is caused by improper cam lobe hardening at the factory. A valve guide that is working out, could be more pressure on the lobe, if the rocker is hitting the guide, but normally the guide moves quick enough that it just bends the pushrod.
That's probably it. I believe I probably thought "WTF" is wrong with this thing and the valve gear failed. So IL ENG it is a quality problem at the cam mfgr or BS problem accepting the cams on "certs," instead of some incoming sampling at receiving inspection. Seems like a little "Japanese" quality would help?
#10
Fish
The cam lobe failures that I see are on the Intek twins @ 2004 or so.
One of the 4 lobes rounds off, usually closest to the gear, others look fine.
UPDATE: I pulled the oil sump / oil pan and lifted it off careful not to damage the lower crankshaft seal. I cleaned and lubed the lower crankshaft and eased it off. However the pan gasket was toast since it was glued on at the factory. What I found was a perfectly intact, new looking camshaft! When I tried to remove the Intake Lifter it wouldn't budge. (That was the original problem...the intake pushrod wouldn't move and the rocker arm was dangling and the tower bolt was backed out about 3 or 4 turns, so we all assumed a worn lobe) I put the pushrod back in and pushed first one way and the other and finally broke it loose! The exhaust lifter came right out with no problem. It seems to me there was an awful lot of play in the push rods side to side. On the top end where the push rods exists the block there are two black plastic square bushings. It doesn't keep the push rods in line at all. The only thing I can come up with troubleshooting why the intake side failed is that the rocker arm tower had backed out about 1/4" and that would give enough play for the rocker arm to come off the push rod. Why the intake lifter stuck off the lobe and in the bore is anybody's guess. Varnish deposits? Any ideas?
#15
Fish
Yes, that was your only problem.
You just didn't hit the lifter when you re-installed the pushrod.
I'm going back together with it now and have the camshaft in and the intake and exhaust valves roughly set tight enough to hold some tension on them for a final adjustment in the morning. Scraping that old gasket material off the engine and oil pan took the longest time. I like to pull an engine through a few rotations by hand before I fire it off, just to see if anything is amiss. Hopefully the oil pan, gasket, cam, governor and oil pump shaft etc. will all line up the first time. We'll see if she fires off and runs tomorrow!
