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Craftsman tractor - B&S sudden failure

Posted by MikeK1005 CT (My Page) on
Sat, Nov 23, 13 at 15:56

A little back story first...I was nearly finished mowing the neighbor's 1/2 acre yard (and planning to start on my own), when suddenly - and without sound or other indication - the machine (Carftsman YS4500 with B&S 21 HP OHV : 331877 0805 E1) just stopped dead. I tried to start it again - the motor turned over slow/hard, but wouldn't fire up, so I pushed it into the garage for further diagnostics

I checked all the basics - I'm getting spark, I have compression, air filter is clean, fuel flows freely through the inline filter and there's fuel in the carb bowl. One thing I noticed was that despite repeated efforts to started the engine, it never smelled like it was flooded...

I'd adjusted the valve clearances in the beginning of the season and the tractor was running great. And having read much in this forum, I understand how much a simple little adjustment can impact engine starting/performance. So my next thought was to remove the valve cover and check the clearances again...although not understanding how this would explain the sudden engine stoppage. I removed the spark plug (and oh yeah, I forgot to mention that I noticed earlier how much easier the engine turned over when I'd removed the plug to check for spark) and turning the flywheel by hand, I was surprised to notice that the valve assembly was not moving one bit. I completed several rotations, and with a sinking feeling in my stomach, concluded that I was not mistaken. The pushrods, rocker arms and valves weren't moving. I removed the rocker arms, and with some effort, confirmed movement of the valve/spring assembly. While holding the pushrods in place one at a time and exerting some inward (horizontal) force, I rotated the flywheel a few more rotations and observed that they weren't doing their pushing, not even a tiny little bit that I could feel.

I have a little knowledge of the theory of IC engines, but don't claim to be well-versed in their various designs, so I spent some time on YouTube reviewing the mechanics particular to an OHV engine, noting a few elements that I found to be significant: 1) the crank drives the camshaft via interlocking gears, 2) timing is determined by aligning marks on these gears, and 3) the nature of the cam is that it possesses lobes that drive the pushrods. And here's where I sit now. I don't want to tear down the engine without knowing that it's necessary. And I know if it comes to that, I'll need to order the Briggs engine manual, replacement gaskets, etc, plus a replacement for whatever parts are determined to be faulty. I'm not afraid of the work, but I don't want to do it unnecessarily.

Walt Conner - I'm a big fan of yours since first finding this forum...hoping you or a colleague can help out yet another distressed homeowner & DIY'er. It won't be long now before we have our first snowfall and I'm looking at a yard full of leaves...much gratitude goes out to anyone who can lend advice for getting my machine running again!


This post was edited by MikeK1005 on Sat, Nov 23, 13 at 16:15

Follow-Up Postings:

RE: Craftsman tractor - B&S sudden failure

First, let me apologize for this not really being a properly helpful response. That said, I have a similar machine, and can tell you from direct experience that, with the engine info you've posted, you should have no trouble getting a PDF copy of the manual for both the tractor itself and the engine. The briggs archives are surprisingly deep, and their search tool makes the process just about foolproof.

And now my one hopefully-useful question: when you had the valve cover off, could you see down into the shafts the pushrods live in at all? In my engine, there's a metal plate with plastic guides, that keeps the top end of the rods in line with the rockers, but below that, it's just open. It almost sounds as if the pushrods had lost contact with the cams, which actually happened with one of mine not too long ago. So this'll sound a bit like blaming the victim, for which I apologize, but here's my one crazy guess, based on what you've told us...

If there's any chance that, when you adjusted the valve clearances, you didn't torque down the nuts tightly enough, I can see the possibility that one or both may have worked loose enough that the pushrod(s) could have lost contact with the cam. I'm sure there are a hundred better explanations for what you're seeing, but it does seem to fit the symptoms, and it should be fairly easy to check. (On my engine, all I needed was a 10mm wrench to take off that plate; once it was off, I could see down in there, no problem.)

Good luck!

RE: Craftsman tractor - B&S sudden failure

I'd say that if the tappets aren't moving (where the rods insert into) - it needs to be split so you can investigate further. Gear/ cam will have a story to tell.

RE: Craftsman tractor - B&S sudden failure

Thank you fearboy for such a quick reply! I have already been able to acquire both the owner's/service manual and the illustrated parts reference online. The parts guide is even linked to the B&S store so I can order virtually everything I'll need...once I figure out exactly what all that is anyway.

As you described, I had removed that plate with a 10mm wrench (gonna be asking Santa for a small metric deep socket set...) and saw down into the shafts. At the other end, I assume I was looking at the "cam followers". When I described my test while holding the pushrods "in place", I neglected to mention I did this both with that plate installed and removed.

As I was in unfamiliar territory, I tried what I thought was how things would align...but with your fresh advice, I went back for a second look. I included an image this time. It's a shot of the top channel behind that plate through which the pushrods are installed. I believe what I'm looking at here is that the exhaust tappet (thanks for the correct verbiage tomplum) is the top circle... and I'm guessing the bottom circle (the center of the complete pushrod region) is a port for lubrication? I have another shot down the intake shaft and I can see another tappet for the intake pushrod. Aligning a pushrod into either tappet and hand-turning the flywheel produced absolutely no movement.

Does anyone know if the cam lobes or gear teeth are ever known to fail or break? Are there any other possible explanations for why I can confirm piston movement but not valve movement? Again, before I commit to a tear-down, I'm hoping to rule out all less-involved repairs...actually, I'm hoping there IS some less-involved repair. Thanks again for all responses!

RE: Craftsman tractor - B&S sudden failure

Concur with tomplum. If there is no movement at all in the tappets/push rods..........there has been a sudden failure in the camshaft driving parts, and that is a most unusual type of failure.
I doubt that you are actually getting "genuine compression" as defined by a mechanic, but you probably are just feeling the effects of a good piston/rings and seated valves which are sort of mimicking true, cyclic compression events.
You will at least need to remove the sump cover for further reviewing.

I came back to edit this as you posted another entry while I was working.
I see what appears to be some "torn up" metal in your photo (I have marked with arrows).
Post further photos of your findings as you progress please.

This post was edited by mownie on Sat, Nov 23, 13 at 20:34

RE: Craftsman tractor - B&S sudden failure

Thanks mownie...looks like I'll be borrowing a machine to get the leaves off the ground for this season.

I attached a shot of the intake channel - I was suspicious of the opening below the tappet - not sure if that too is of any concern (not that one tear in the housing isn't enough for a complete failure).

I intend to tear down the engine over the next week...might not have anything more to share until next weekend, but I do really appreciate the responses from you, tom and fear... happy Thanksgiving to all!

RE: Craftsman tractor - B&S sudden failure

Mownie and company, I'm sharing one more pic - a more in-focus image of what appeared to be torn metal. I believe that this is merely the cylinder wall housing. Please take a you agree?

Any thoughts on the exposed region below the intake tappet in the prior pic? Intended design or potential damage?

RE: Craftsman tractor - B&S sudden failure

Dear Santa-
I've been a good boy this year and all I want is
331977-0001-G1 -Mike (cookies and milk on the mantel ;)

RE: Craftsman tractor - B&S sudden failure

The more in focus photo does take away some of the previously disturbing appearance of the "metal" I saw first.
That better, clearer photo appears to show only the curvature of the cylinder below the juncture point of the cylinder head and cylinder block (aka crankcase). The black "fuzzy looking" material is likely just a bit of the edge of the head gasket showing.
While this does clear up that there is no torn up metal in this area, there is still to have a peek inside after removing the sump cover.

RE: Craftsman tractor - B&S sudden failure

We're pulling for you Mike. It is a different perspective from a normal repair situation. You don't ever really pay that much attention to the galley area- other than to keep it clean when doing a head gasket. The new photo is clearer in front. Things look sketchy behind the return hole. Something came apart? This could be interesting!

RE: Craftsman tractor - B&S sudden failure

concur with the others - i'm thinking you're gonna have to get inside there. by way of commiseration, i can tell you that i had to go into mine three times over the past 2 weeks; once to do rings & head gasket, the second time to fix the timing (which i'd completely neglected to check the first time through - nothing funnier than a geyser of gas & oil shooting up through the air intake!), and then again for some other damn thing i've now blocked out. oh, and one of those times, i got it all put back together, then found the governor on the bench. that made me feel reeeal smart.

anyway, we're rootin' for ya. one last piece of advice: if you haven't already, invest in a tube of permatex - really good for replacing the gasket on the oil sump.

happy hunting!

RE: Craftsman tractor - B&S sudden failure

***"Any thoughts on the exposed region below the intake tappet in the prior pic?"***
As tomplum said, we seldom have a reason to look closely at things that are not part of a repair job we might be engaged in, so we usually do not have a visual memory of how "normal" parts look.
Only when we are faced with a failed component do we tend to gather visuals of different perspectives.
Focusing on the view you mention above, I see what might be a "separation failure" in the camshaft (red arrow).
But that "suspicious area" might just as well be nothing but an intentionally machined area of the cam lobe that is a "press fit" onto the central portion of the multi-piece camshaft assembly.
Is that the spot you were referring to?
And DO NOT use any type of RTV or "Permatex" as a substitute for the sump gasket.
The sump gasket is a specific thickness of material that is factored into setting the dimensions of the assembled sump cover to the engine crankcase.
Using RTV or other sealants to replace that gasket is going to skew the design dimension of the crankcase, and that has an effect on bearing clearance and end play of the crankshaft and camshaft.

This post was edited by mownie on Sun, Nov 24, 13 at 12:24

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