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dhoadley

Here's a real puzzler.

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dhoadley

This Tecumseh cam is from my brother-in-law's 40 year old Ariens snowblower. Last winter it stopped very abruptly after 5 minutes of WOT. I have a similar machine that was not working so well, so he thought I could use it for parts. I got mine running well enough that I never cannibalized it and thought I would do a post-mortum. I had expected to see a broken rod, but found this instead.

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The rest of the motor looks great, very smooth surfaces and the valves move freely.

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How do you guys get such great photos? My auto-focus point-n-shoot needs to get upgraded someday. I threw away a half a dozen shots of the break.

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The bearing surfaces look great.

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I got a valve spring tool recently, so I thought I would remove the valves to clean and evaluate. I'm thinking of just replacing the cam and letting her rip. Anything else I should look for? Why would this have broken.:II know this is slightly far afield for this forum, but I feel like I've gotten to know the regulars here as I read all the day's posts every morning over coffee. Other forums might be more appropriate, but they are strangers to me, and I know the wealth of knowledge here will serve me well. Thank you for allowing me to hang with you guys this past year to share in your trials and triumphs. Dave

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P3120338.JPG.d870c691af440bbbc63e1a5f85f82ed8.JPG

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ReedS

Way back in high school engine shop, I played with a couple of tecumsahs, and was successful in blowing them up easily. It just looks to me that the point of failure is a weak point in the cam where there is considerable horizontal stress on the cam lobes (esp @wot)and where it meets a relatively large verticle surface with a small section of joining material.

May just be the result of overspeed and fatigue, replace the cam, adjust the wide open throttle limit.

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dhoadley
quote:Originally posted by fishnwiz

Set your camera on Macro for tight shots.


id="quote">
id="quote">Macro? There's a little dial that shows a hand waving, a person's head, a mountain, "scene", "guide", a movie camara, "auto", and "P". Are any of these "Macro"? Thanx, Dave

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fishnwiz

Not sure what the P stands for.The macro setting is sometimes a flower. Most cameras have a macro setting of some sort. If you do not have your manual, look it up on google using the model number off of the camera and go to the index in the manual and find the macro setting symbol as this is what you need to set your camera on for extreme close settings.

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ZippoVarga

If you have a tri-pod, set the camera on it if it's equipped with the threaded base and scroll through each setting with the camera at no closer than 4 inches. The camera will tell you if its on the right setting by giving you a red field of view box when the shutter button is partially depressed. This has been an industry standard for a few years. Another possibility, is to set the camera to "easy"...then it should set it self when you have the field of view mere inches from the object. And yet another option, take the highest resolution possible and as close as you can and still focus well, then open the photo and enlarge it until you get the detail you like, then crop out all the extra that isn't important in the photo.

First problem is, it's a Tecumseh...lol. Sorry....I just don't like the little things. But.......I believe Reed is spot on. Weakest link scenario. Set low idle to 1100 RPM and high at a max of 3600. Laser tachs can be purchased on Amazon for 15 bucks and are real engine savers!! That, or, if you're lucky enough to have a friction tachometer, you're in rare company with only a few of the old timers around and can use it. Or sell it...like to...oh, I don't know...uh....ME! lol Cheers!! Zip~

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dhoadley

I know the Tecumsehs have a rep for throwing rods, so I thought this would be a good opportunity to get a small engine tach. The 6 hp. that is on the ancient Ariens now runs too slow and I need to adjust the high speed up, I just need to research how that's done. It'll just have to wait its turn as I think we're past big snow here in southern New England:J, and I have a free Gilson walk-behind rototiller that I'll be needing soon. Thanx, Dave

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BLT

If you Google "TEC 692509", you can download a free repair manual and that should show you what you need. If you read Al Eden's governor settings article and remember the theory, governor settings are like shooting fish in a rain barrel.;)

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toomanytractors

I had a cam break the same way on a riding mower about 45 years ago. My brother in law welded it back together and the last I knew of it about eight years later it was still running.

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dhoadley
quote:Originally posted by BLT

If you Google "TEC 692509", you can download a free repair manual and that should show you what you need. If you read Al Eden's governor settings article and remember the theory, governor settings are like shooting fish in a rain barrel.;)


id="quote">
id="quote">Bob, Never thought to look under "articles". That was simple and easily understood. Now let's see if I can apply it!;) Thanx, Dave

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dhoadley

I got a replacement cam off of Ebay. There are no marks on the crankshaft gear, that I can see. Anyone know how to time up the camshaft with the crankshaft on these old H-70's? Thanx, Dave

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dhoadley

Bob, you were right, it was in that manual on page 87. You line up the keyway on the crankshaft with a small "hobbing" hole in the camshaft gear. Every other one I've ever seen (admittedly not a ton) had marks on the teeth. Thanx for the guidence, Dave

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