Posted by LJD on May 11, 2012 at 14:18:40 from (75.250.222.133):
I've been hearing the many stories for years about the results due to a lack of unleaded gas in older machines. Many say it's all nonsense and some (like me) believe test results.
I've read test after test that an engine that lacks hardened valve seats suffers valve-seat recession if used long and hard.
Well it just happened to me.
I've got a 1010 gas crawler with an engine I rebuilt maybe 10 years ago. I personally did the valve job so I know exactly what condition the valves and seats were in. Wasn't too bad when I got it, but I recut/reground the valve faces and seats - all to specs. I did NOT install any seat-inserts that would require machining the heads to accept them.
Up to last month, I've never really used my 1010 long and hard. It's gotten plenty of use, but intermittent.
This Spring, I've been building a pond. Much of the work was done with my Allis HD6 and huge Pettibone backhoe/loader. But - I wound up using the 1010 crawler-loader much more then planned since it can get around on mud and has a bucket to transfer fill around. I used it heavy, all day, every day (more or less) for three weeks. I finally literally ran the tracks off it. I was almost done when the tracks were so bad I could no longer could keep them on. So, I pulled the crawler in my shop and started tearing down the undercarriage. It's been in my shop now for two weeks. Note that when I pulled it in the engine ran perfect. Purred like a kitten, no smoke, great power, etc. But on that last day of use it started getting hard to start. Once running, it was fine. After getting in the shop and needing to start it once in awhile to move sprockets, lift in the air, etc. it got even harder to start. Finally yesterday - I could not start it no matter what I did. I was kind of stumped. I usually try to be smart and diagnose problems. This time - in desperation - I changed the spark plugs, played with the timing, pulled the carb apart, etc. After nothing worked - I reluctantly did a compression test, which seemed absurd to me. An engine I knew ran perfect and rebuilt not very many hours ago? Well guess what? At cranking speed, #1 had 0 PSI, #2 had 75 PSI, #3 had 60 PSI, and #4 had 0 PSI. If hadn’t seen it, I would not of believed it. So I took off the hood, gas tank and valve cover and checked valve lash clearance. The intakes were fine and still at .012" like I put them at 10 years ago. The exhaust valves? None were closing. Less then 0 clearance. Since the intakes were still correct, I cannot blame this on the head-gasket or sleeve-deck-gasket shrinking. It has to be exhaust valve seat recession. So, I loosened the valves and now have 130 PSI on each cylinder. I assume when I get it all back together it will start fine. Now I'm thinking of using a valve-recession additive since I'm not eager to pull the head, machine for valve seat inserts, pay a fortune for gaskets, etc. I DO wish I had done that years back. I have the equipment to reface valves, grind or cut seats,, knurl valve guides, etc. I do NOT have the equipment to bore the heads for seat inserts. There is also no local machine shop around anymore to do it.
The seemingly odd thing is it ran great once running. I'm assuming it got to the point that when at running speed, there wasn't ample time for the compression to leak past the valves fast enough to affect anything. But at cranking speed - it lost compression as fast as it could make it - and ergo - no start.
A friend of mine recently had a similar problem with his Ford diesel tractor. But in his case - it was a month after installing a new head gasket. It "settled", i.e. became thinner under pressure. This caused the engine to loose all the valve clearance since the pushrods were pushing further into the head. When I checked it for him, he had no clearance on the intakes or the exhaust.
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