l008com
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- May 25, 2015
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I want to keep this brief but I also want to give you the full backstory.
I need help assessing what happened to this machine, and what it's current condition is.
This is a Craftsman Yardvac with a B&S 675 engine. It was in my neighbors yard never being used for 15 years or so, and one day he gave it to me.
I drained the gas and the oil, refilled both, and more or less was able to start it right up.
While it was running, I noticed some sparks flying out. I though this was just leaves on the muffler that were burning. But it kept going and now I think it was leaves all up around the flywheel obstructing air flow.
So the machine was running and running well for maybe 15 minutes to a half hour or so. Then is sputtered a bit, then died out. Kind of like it was out of gas, but maybe a little more abrupt. Also it was not out of gas. When I tried to restart it, at first there was no resistance at all. The engine would spin freely like the valves were stuck open. After a little while, suddenly the compression was back but still no starting. Eventually I took the engine head off and confirmed that both valves were moving fully and properly seating. But what I didn't realize at first was that they timing of the valves was way off. Intake-Compression-Power-Exhaust, thats NOT the order the valves were opening and closing in! After a little research, I decided that there must have been way more junk up under the plastic engine cover than I realized, and I must have overheated the engine, causing the plastic camshaft to melt.
It made sense!
Tonight I finally got the engine off and took the engine block apart.
Here's where I could use some second and third opinions to what I'm seeing.
First off, much to my surprise, the camshaft looks perfect. I thought the lobes were going to be partially melted and distorted but they look perfect to me!
But it turns out, the small plastic gear on the crankshaft, that turns the camshaft, that might be where the problem is. it has a plastic notch that fits in to a notch on the crankshaft, and it looks like it is completely melted and smooshed. With that gear on the crankshaft, you can spin the gear easily without spinning the crankshaft. At first, that seems like the obvious cause of all this. But if it can spin THAT freely, wouldn't the valves not be opening at all? And why would just that one plastic nub melt, but none of the rest of the plastic in there?
Back to that camshaft, I said it was perfect but actually there is one flaw. The tip of one of the lobes does appear to have a little bit of damage. Not much though, I don't think this is causing any problems. But I'm curious what would cause that. Super hot valve rod maybe? Or maybe just a stuck valve rod causing the plastic lobe to be the weakest link? I'm thinking that with everything else fixed, this isn't a problem?
Now lets talk about the oil. I changed the oil right before I started it up, so it had at most half an hour on it. I believe it was 5w-30 either full synthetic or semi-synthetic. When I cracked the crank case open, the oil that leaked out was very grey. I expected it to either be gold still like new, or brown like it was burned. But grey, that suggests metal wear. But what metal would be wearing? I drained the bulk of the oil before I removed the engine, I don't remember it being discolored but its possible I just wasn't paying much attention to the oil's color then.
So whats your take on all this?
The simplest solution I can see is that there was too much crap around the flywheel, the engine overheated, that caused the tab on the crankshaft gear (timing gear?) to partially melt and slip, but then somehow grab again, so now the valves are opening and closing but out of timing by a mile. Meanwhile during overheating, one of the valves stuck temporarily but eventually loosened up and started working normally again.
Am I missing something? Or making incorrect assumptions I'm not seeing?
The one good thing here, is that this is a yardcvacuum. So its going to be seeing probably 5 hours of runtime at most, per year. So if I've set the engine down the path of premature failure, I'll still probably get a lot more years out of it until then.
Right now my plan is to replace that crankshaft gear (timing gear?), and of course the engine seals, put it all back together and hopefully that fixes everything. Unless we come to some different conclusions in this thread.
Also, side note. I have the model number of the whole machine itself (247.77013.0) but I cannot find a model number ANYWHERE on this motor. It has a decal that says 675 series, but no numbers. And I need a number to be able to look up engine parts. How can I figure out this ENGINE model number?
I need help assessing what happened to this machine, and what it's current condition is.
This is a Craftsman Yardvac with a B&S 675 engine. It was in my neighbors yard never being used for 15 years or so, and one day he gave it to me.
I drained the gas and the oil, refilled both, and more or less was able to start it right up.
While it was running, I noticed some sparks flying out. I though this was just leaves on the muffler that were burning. But it kept going and now I think it was leaves all up around the flywheel obstructing air flow.
So the machine was running and running well for maybe 15 minutes to a half hour or so. Then is sputtered a bit, then died out. Kind of like it was out of gas, but maybe a little more abrupt. Also it was not out of gas. When I tried to restart it, at first there was no resistance at all. The engine would spin freely like the valves were stuck open. After a little while, suddenly the compression was back but still no starting. Eventually I took the engine head off and confirmed that both valves were moving fully and properly seating. But what I didn't realize at first was that they timing of the valves was way off. Intake-Compression-Power-Exhaust, thats NOT the order the valves were opening and closing in! After a little research, I decided that there must have been way more junk up under the plastic engine cover than I realized, and I must have overheated the engine, causing the plastic camshaft to melt.
It made sense!
Tonight I finally got the engine off and took the engine block apart.
Here's where I could use some second and third opinions to what I'm seeing.
First off, much to my surprise, the camshaft looks perfect. I thought the lobes were going to be partially melted and distorted but they look perfect to me!
But it turns out, the small plastic gear on the crankshaft, that turns the camshaft, that might be where the problem is. it has a plastic notch that fits in to a notch on the crankshaft, and it looks like it is completely melted and smooshed. With that gear on the crankshaft, you can spin the gear easily without spinning the crankshaft. At first, that seems like the obvious cause of all this. But if it can spin THAT freely, wouldn't the valves not be opening at all? And why would just that one plastic nub melt, but none of the rest of the plastic in there?
Back to that camshaft, I said it was perfect but actually there is one flaw. The tip of one of the lobes does appear to have a little bit of damage. Not much though, I don't think this is causing any problems. But I'm curious what would cause that. Super hot valve rod maybe? Or maybe just a stuck valve rod causing the plastic lobe to be the weakest link? I'm thinking that with everything else fixed, this isn't a problem?
Now lets talk about the oil. I changed the oil right before I started it up, so it had at most half an hour on it. I believe it was 5w-30 either full synthetic or semi-synthetic. When I cracked the crank case open, the oil that leaked out was very grey. I expected it to either be gold still like new, or brown like it was burned. But grey, that suggests metal wear. But what metal would be wearing? I drained the bulk of the oil before I removed the engine, I don't remember it being discolored but its possible I just wasn't paying much attention to the oil's color then.
So whats your take on all this?
The simplest solution I can see is that there was too much crap around the flywheel, the engine overheated, that caused the tab on the crankshaft gear (timing gear?) to partially melt and slip, but then somehow grab again, so now the valves are opening and closing but out of timing by a mile. Meanwhile during overheating, one of the valves stuck temporarily but eventually loosened up and started working normally again.
Am I missing something? Or making incorrect assumptions I'm not seeing?
The one good thing here, is that this is a yardcvacuum. So its going to be seeing probably 5 hours of runtime at most, per year. So if I've set the engine down the path of premature failure, I'll still probably get a lot more years out of it until then.
Right now my plan is to replace that crankshaft gear (timing gear?), and of course the engine seals, put it all back together and hopefully that fixes everything. Unless we come to some different conclusions in this thread.
Also, side note. I have the model number of the whole machine itself (247.77013.0) but I cannot find a model number ANYWHERE on this motor. It has a decal that says 675 series, but no numbers. And I need a number to be able to look up engine parts. How can I figure out this ENGINE model number?
