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Rick
Rick, Factory Authorized Trainer
Category: Small Engine
Satisfied Customers: 8057
Experience:  Outdoor Power Equipment technical trainer since 1990, covering eight states.
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Techumseh 17.5 OHV engine. Starting problem. Have adjusted

Customer Question

Techumseh 17.5 OHV engine. Starting problem. Have adjusted valve lash, but still hard to turn over, actually stops each time it reaches peak compression. Inspected starter for internal problems and it is okay. Battery is new, has higher CCA (420) than original. Battery reads 13v. With starter engaged, volts at starter reads 10v. Connections at battery and starter have been cleaned. Have tightened adjuster nut on rocker arm to a no clearance position, but didn't help. What should I be looking at?
Submitted: 5 years ago.
Category: Small Engine
Expert:  Rick replied 5 years ago.
Hello, and thank you for choosing JustAnswer. I'll be helping you today and am committed to providing clear and concise answers to your question.

Does it turn over normally with the spark plug removed?
Customer: replied 5 years ago.
Hi Rick

Engine does turn over with plug removed, but it seems like it is not as robust as it I think it should be.
Expert:  Rick replied 5 years ago.
Let's verify that the valves are indeed adjusted at .004" on both, correct? Once we're sure of that, next let's check the compression release. Remove the rocker box cover and watch the action of the valves as the engine is cranked over slowly. It's best to do this by rotating the crankshaft by hand if possible, but you can do it with the key switch or recoil starter if your eyes are quick. Look for both valves to open and close fully, then check if one valve is opening and closing just slightly. This slight movement of one valve is the action of the compression release if it's functioning properly.

Let me know, please. Thank you.
Customer: replied 5 years ago.
Your last statement confuses me. There is only one way to adjust the valve clearance that I am aware of, and that 'is' with the rocker arm adjustment at .004". Am I wrong? Anyways, I have performed this action previously, setting the rocker arm adjustments, and still ended up with difficulty in turning engine over with starter. Several things there to verify before moving on further I think.
Expert:  Rick replied 5 years ago.
They could be set incorrectly at .002", .010" or any other specification one would care to use on the feeler gauge. .004" is correct, but you would be amazed how many times I've asked and the operator had them set .007"-.009" like Briggs. Just verifying.

The reason I verify is that an out-of-spec valve will not allow the quick test I asked you to perform to check the compression release to be valid. At least not if they are too loose. This process is the ONLY way to check if the compression release is working.
Customer: replied 5 years ago.
Okay. I will have to go out to garage and do this again to verify, but I have done it before and when I was done, my sense was that the compression release was not working at the desired setting. That is why in my original question, I indicated that I had reduced the setting to '0' and was still experiencing a problem.

Not to get ahead of you, but is the 10v reading on the engaged starter normal?

I will wait for your next response, before I go get my hands dirty. :)
Expert:  Rick replied 5 years ago.
It's slightly borderline. A battery should not drop more than 2 volts when using the starter, but 10V is a normal reading, althogh I'd like to see 10.5V. Your 13V reading is just a tad high, so you may have been reading a bit of residual "float" voltage from the charging system. A fully charged battery at rest should read about 12.6-12.7V.

And we're thinking alike. Once we verified the compression release by that slight valve opening I was going to explore what you meant by not as "robust". Since you replaced the battery and cables I would also ask once we verify the release whether the engine seems to turn over easy by hand with the plug out to eliminate any internal binding or parasitic loads.

I'm leaning at this point toward a faulty compression release based on the symptoms you describe and the frequency it occurs on Tecumseh OHVs. I love the engine, and it was my primary dealer line for many years, but I also admit to their weak spots. And the compression release was one of them.
Customer: replied 5 years ago.
I can verify from my working on this engine last week, that after I completed the valve setting adjustment, the engine turned over by hand, spark plug removed, without any difficulty. However, with plug in place, it was very difficult to get the engine to start without having the old battery with charger on, to turn engine strong enough to get it started, That is why I got the new battery, thinking it was the problem.

From what you said so far, and my experience for the last couple years of having to charge the battery every time before starting the engine, the compression release seems to me to be the problem. Are we talking about a new camshaft as the eventual solution?
Expert:  Rick replied 5 years ago.
Not necessarily. Can you provide your complete model and spec number, please? In later years, we beat Tecumseh up pretty good about this issue and they came up with a kit that fits the newer OHVs to replace just the flyweight and spring without having to replace the entire camshaft. Still a pain to take the engine apart but the difference was considerable in the price of the failed part. With your model and spec number I can verify.
Customer: replied 5 years ago.
I must apologize for not getting back to you last night. Seems the computer I was using decided to stop updating and I thought you were gone instead. Anyways from my office pc this morning I've got your last message and here is the info you requested.

Tecumseh OHV 17 204605B
Engine family STP 490U1G2RA
Displacement 490 D.O.M. 8126 S
Customer: replied 5 years ago.
IGNORE THIS REPEAT POST Sorry, refreshed other pc and post was resent.


I can verify from my working on this engine last week, that after I completed the valve setting adjustment, the engine turned over by hand, spark plug removed, without any difficulty. However, with plug in place, it was very difficult to get the engine to start without having the old battery with charger on, to turn engine strong enough to get it started, That is why I got the new battery, thinking it was the problem.

From what you said so far, and my experience for the last couple years of having to charge the battery every time before starting the engine, the compression release seems to me to be the problem. Are we talking about a new camshaft as the eventual solution?
Expert:  Rick replied 5 years ago.
Good news. There is indeed a camshaft repair kit for your unit for a fraction of the cost of a new cam....

Tecumseh 730656

I've linked the part number to a shopping search, or it can be ordered though a local Tecumseh dealer.

Keep me posted and let me know if I can assist, please.
Rick and 3 other Small Engine Specialists are ready to help you
Customer: replied 5 years ago.
Thanks Rick for expert advise. I'm compelled to tell you that after visiting many well meaning forums and salesmen of parts companies, that they all failed to come up with what I thought and you confirmed was the problem.

One last thing as I begin the tear down and rebuild project, is there a step-by-step instruction available? I probably can wing it, but it would be nice to have the official instructions if available.

Thanks again.
Expert:  Rick replied 5 years ago.
Thank you for your kind words and for being a great customer to work with. While not exactly step-by-step, here's a shop manual and parts list that should be helpful:

Manual

Parts List

Best of success with all your hands touch....