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  #1  
Old 03-24-2021, 11:04 PM
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Cubcadet_107 Cubcadet_107 is offline
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Default Bent Valves?

Well, today I picked up a free Ariens front-tine Rototiller from the side of the road, the classic "this has been sitting in the corner of the garage for years, it'll take way too much work to get it going again" story. Upon initial inspection I noticed almost no compression, though you could feel the piston moving still. No stuck valves, but the head gasket was junk. No big deal, I've got plenty of spare Briggs parts around. But once back together with a new gasket the compression was still really low.

It was at this point I realized that the head of the intake valve seemed to have a slight tilt to it. I pulled it out, put it back in and rotated it by hand, and sure enough, one half of it seated while the other didn't. On the side that didn't seat you could see a small gap between the valve and block. Who woulda thunk?

Again, I've got a ridiculous amount of spare parts for these, so I stole a valve off a nearly identical parts engine. Compression is much better with the replacement valve. Interesting side note, this is the first Briggs engine I've seen with a 2nd output on the camshaft. It runs the tiller tines in reverse.

But anyway, how common is this? And what causes it? Perhaps a major backfire? I haven't checked the points and timing, perhaps it's way off? Any insight is welcome here.
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Old 03-25-2021, 03:55 AM
Bryan S Bryan S is offline
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Don't really know on the little engines but on the Chevy V8's,
there's a laundry list of things that can cause a bent valve.
Maybe some can translate over, the first one most likely does not.
Novice engine builders put high lift cams in with out upgrading the
valve springs, valve hit's top of piston, bends valve and does damage
to the piston. Broken valve spring and or keeper, valve hits... wash,
rinse repeat.
Improper deck clearance, head milled too much,
wrong head gasket, not enough valve to piston clearance,
wash rinse repeat. Over revved the engine, little one had a governor go rouge on it? Just some of the many, many
things that can happen on the V8's.
When the pistons start swapping holes, you gots yourself some BIG problems, and BIG bills.
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Old 03-25-2021, 07:52 AM
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Well, this is a little old Briggs flathead engine, so nothing with valves hitting the piston apply here. Nothing has been milled, and I don't think the valves have been messed with. At the end of the day, this IS just a little old tiller engine.

My best guess of the list you've provided is, that someone over revved it, as there is a bit of custom made governor linkage that I'll probably replace with a proper piece from my parts engine. Either that, or the timing is way off and it suffered a backfire. Tonight I'll be tearing further in so we'll find out!
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'70 107 with k301 engine swap
'71 106 with 38" deck
'70 147R with factory replacement k321, 42" deck
'61 Original with 38" timed deck
'63 70 "pinkie"
1863 with 54" deck
'46 Farmall H, '50 Farmall Cub

105 x2 (parts)
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Old 03-25-2021, 02:14 PM
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I doubt a backfire can bend the valves. Bryan stated a lot of good reasons. Did you look at the head for impact damage?
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Old 03-25-2021, 03:12 PM
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From a quick inspection there does not seem to be any evidence of a valve hitting the head. But when I get home I'll give it a closer look.
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'70 107 with k301 engine swap
'71 106 with 38" deck
'70 147R with factory replacement k321, 42" deck
'61 Original with 38" timed deck
'63 70 "pinkie"
1863 with 54" deck
'46 Farmall H, '50 Farmall Cub

105 x2 (parts)
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Old 03-26-2021, 12:45 AM
Bryan S Bryan S is offline
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In between watching my fuel gauge drop like there was
a hole in gas tank today on my trip up and back to NY,
I was thinking about possible things that could cause a bent
valve in the little Briggs. I wondered aloud if maybe from sitting,
the valve stem had gotten seized up a little and when it was
turned over it caused the bent condition.
See if you can find any pitting or marking/marring on the stem.
If the valve did hit something, it would just be small nick like,
not even quarter moon/round size. Prob would be a very minimal mark.
Really that's all I can think of is being over revved and maybe a stuck
valve from sitting.
Hope you can find out the cause.
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Old 03-26-2021, 07:51 AM
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Those old bullet proof flathead B&S engines, will warp an intake if one runs then hard, like tilling, with a bad head gasket.
And as far as a PTO on the camshaft, they were/are popular on tillers.
They were in competition with Tejunkski engines built in the day.
( they always outlived the tillers) unlike tejunkski's that done blowed the rods out the side of the blocks.
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Old 03-26-2021, 09:43 AM
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Quote:
Originally Posted by ol'George View Post
Those old bullet proof flathead B&S engines, will warp an intake if one runs then hard, like tilling, with a bad head gasket.
And as far as a PTO on the camshaft, they were/are popular on tillers.
They were in competition with Tejunkski engines built in the day.
( they always outlived the tillers) unlike tejunkski's that done blowed the rods out the side of the blocks.
George, I think you've just figured it out. The head gasket that I removed from this engine was most definitely bad, as I had to scrape pieces of it from the head and block. There was no damage to the head that would suggest a valve hitting it, and the valve stem was smooth with no damage either.

On a side topic, I've actually got a 2nd one of these tillers, an earlier one complete with a Tejunkski that somehow isn't blown up. It's being used as a parts tiller for this one.
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'70 107 with k301 engine swap
'71 106 with 38" deck
'70 147R with factory replacement k321, 42" deck
'61 Original with 38" timed deck
'63 70 "pinkie"
1863 with 54" deck
'46 Farmall H, '50 Farmall Cub

105 x2 (parts)
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