B&S 675 Series Camshaft Problems? Overheat? What did I do?

[Tiger Small Engine]

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!
View attachment 70375

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?
View attachment 70376

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?
View attachment 70377

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.
View attachment 70378

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?

If you pull the engine shroud and it is packed full of grass, dirt, and debris, then it may have overheated. If the cam is messed up, then replace it while you are in there, and it is cost effective. These engines are generally not worth spending a lot on. Finding the model, type, and code is pretty basic information that is needed.

 

[StarTech]

Considering this unit as manufacture in August of 2008 I am surprised those paper labels has survive to date.

 

[l008com]

Look at the metal cover. There is a metal flange that sticks out over the muffler. the model info is on that flat flange. You can see part of the model number sticking out from under the plastic cover in Star's picture. Looks like 128 of 12B

Its not there. That whole metal cover that goes over the flywheel has zero characters imprinted anywhere.Then inside doesn't have any surface rust, and it makes it much more clear that theres nothing imprinted anywhere. This is truly a ghost motor.

 

[l008com]

Considering this unit as manufacture in August of 2008 I am surprised those paper labels has survive to date.

I have machines from the mid 90s that still have their printed labels on there. This is the first machine I've ever come across that had no marking anywhere at all.

 

[l008com]

If you pull the engine shroud and it is packed full of grass, dirt, and debris, then it may have overheated. If the cam is messed up, then replace it while you are in there, and it is cost effective. These engines are generally not worth spending a lot on. Finding the model, type, and code is pretty basic information that is needed.

The cam looks fine, but the timing gear had some damage. There was some debris around the air flow areas. Not enough that I would think it would cause it to overheat, but maybe it doesn't take as much as I thought. It's certainly worth replacing that timing gear and seeing though.
... IF i am ever able to find out the engine model number.

 

[ILENGINE]

Its not there. That whole metal cover that goes over the flywheel has zero characters imprinted anywhere.Then inside doesn't have any surface rust, and it makes it much more clear that theres nothing imprinted anywhere. This is truly a ghost motor.

It may be my imagination but it looks like you second picture has numbers on that muffler shield. I can make out what looks like 126T0 and a 62 in the corner of the lighter area of rust and looks like a 0 to the left of your thumb.

 

[StarTech]

IL I see the image too of the numbers pn an enlarged image just going have buff the area. They not deeply embossed so lightly buff the area.

 

[l008com]

Now I'm going to have to go look at it again. In the photo, now I am starting to feel like I see something super subtle. But in person, with my own eyes, it looked blank. And I spent a long time looking over that shield again and again, looking at every speck of it. One more close look I guess and we'll see.

 

[StarTech]

Okay let's do this and by the owners manual for the YARD VACUUM. IT has a part list for the 126T02 engine.

https://www.manualslib.com/download/474499/Craftsman-247-77013-0.html

It say use crank timing gear 790345 but depending on the date code is might be 794388

 

[VRR.DYNDNS>BIZ]

According to SearPartsDirect it is a Briggs 126T02-0521-B1 but that is not 100%.

But that engine has four different gears listed. And I have never seen a plastic crank gear until now. I just don't many of that series engines.

Careful look at the shroud as the number should be on it although could be rust covered.

First, an excellent job of reporting the digest of failure. two key points: 1) The cool down may have refused the timing gear to spring the valves while exploring valve motion, usually without compression so motion would not be hindered by other than valve springs. 2) The cam gear also may have failed to maintain position on the cam plus the cost is minimal. Also the dark color indicated it was very hot. I strongly suggest it's replacement. If by now you do not have a good lead on the needed part numbers, repost: