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Donald
Donald, Small Engine Technician
Category: Small Engine
Satisfied Customers: 2188
Experience:  I have 25+ years of experience repairing 2 & 4 cycle engines
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I have a Tecumseh 17 hp ohv engine I race the engine on a

Customer Question

I have a Tecumseh 17 hp ohv engine I race the engine on a lawn mower. It broken many rocker arms. I"ve sure the valves were right.Done it many times.What is the deal?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Donald replied 1 year ago.

Hello, and thank you for choosing Just Answer. My name is***** will be happy to assist you.

Expert:  Donald replied 1 year ago.

How long will your engine run, before your rocker arm breaks? Does it break off near the rocker arm stud?

Customer: replied 1 year ago.
Some times it will go two or three or 7or 8
Expert:  Donald replied 1 year ago.

Are you saying two or three times, or two or three days?

Customer: replied 1 year ago.
No laps
Customer: replied 1 year ago.
u still there
Expert:  Donald replied 1 year ago.

Thanks for your reply. Have you checked to see if your valve is sticking?

Expert:  Donald replied 1 year ago.

Keep in mind that if you are using the correct push rod, this means that our problem has to be valve related.

Customer: replied 1 year ago.
they are working fine when it runs it runs strong
Expert:  Donald replied 1 year ago.

Let's go back. How many rocker arms have you replace already?

Customer: replied 1 year ago.
six or seven
Expert:  Donald replied 1 year ago.

Are they OEM rocker arms?

Customer: replied 1 year ago.
Expert:  Donald replied 1 year ago.

Are you having this problem on your intake side or your exhaust side? These are troubleshooting questions.

Customer: replied 1 year ago.
mostly intake
Expert:  Donald replied 1 year ago.

Are you using a stock cam gear in your engine?

Customer: replied 1 year ago.
No it is a big cam
Expert:  Donald replied 1 year ago.

Have this problem existed since you first started racing this engine?

Customer: replied 1 year ago.
No it run 5 or six races ran great run up front every week
Expert:  Donald replied 1 year ago.

Can you give me a minute, to pull up your engine?

Customer: replied 1 year ago.
yup
Expert:  Donald replied 1 year ago.

Looking over your engine, here are some things I would like for you to check.

Customer: replied 1 year ago.
ok
Expert:  Donald replied 1 year ago.

First check your flywheel key. Pre-detonation could cause our problem. Keep in mind that ignition timing is very critical, when you are racing and revving your engine at high rpms.

Expert:  Donald replied 1 year ago.

The next thing to check, will be your valve springs.

Expert:  Donald replied 1 year ago.

When you are checking your valve springs, rotating your crankshaft until your piston is at Bottom Dead Center. Press each valve in, and feel the pressure on each spring.

Customer: replied 1 year ago.
Key way is good springs they are dubble springs
Customer: replied 1 year ago.
they look good
Expert:  Donald replied 1 year ago.

Thanks for this information. Can I get you to check something for me?

Customer: replied 1 year ago.
ya
Expert:  Donald replied 1 year ago.

I would like for you to remove your spark plug. Shine a flashlight into your spark plug. Take a look at the top of your piston. Check to see if you see any ping marks in the top of your piston.

Customer: replied 1 year ago.
Have done that and no ping marks. Could the valve guides move up and do that?
Expert:  Donald replied 1 year ago.

Valve guides was going to be my next suggestion for you to check. You and I have basically covered everything else.

Customer: replied 1 year ago.
How do you check them
Expert:  Donald replied 1 year ago.

First, remove your valve cover, and shine a flashlight in between your valve springs, to check for obvious movement.

Expert:  Donald replied 1 year ago.

Check to see if your intake valve guide protrudes higher that your exhaust valve guide ...

Customer: replied 1 year ago.
If they have move what would u do to stop it .the valve cover is off. U would have to tack the springs off to do that right
Expert:  Donald replied 1 year ago.

Before removing your springs, remove your spark plug, and rotate your flywheel, check to see if both rocker arms travel the same distance.

Expert:  Donald replied 1 year ago.

If your valve guides are at fault, I would consider replacing the head ...

Customer: replied 1 year ago.
they seem to be good
Expert:  Donald replied 1 year ago.

If you measure the distance, after your rocker arms fully opens your valves, is the distance the same on both valves. Measure from the bottom of your cylinder head, to the top of your valve keeper.

Customer: replied 1 year ago.
the intake valve is a longer valve
Expert:  Donald replied 1 year ago.

Thank you for checking.

Expert:  Donald replied 1 year ago.

Are you saying your intake valve is longer than your exhaust valve??

Customer: replied 1 year ago.
it is sorry I did not see u got back to me
Expert:  Donald replied 1 year ago.

No problem. I would like to make a suggestion to you ...

Customer: replied 1 year ago.
shoot
Expert:  Donald replied 1 year ago.

Ok. You stated that your ignition timing is good, so we can eliminate pre-detonation as a possible cause. This leads me to say, that you and I can reasonably suspect, that our problem is very likely caused by a problem within your cylinder head. I suggest that you remove your cylinder head, and give it a really close inspection.

Customer: replied 1 year ago.
I have had the head off to have seat replaced and found no problem with it at the machine shop
Customer: replied 1 year ago.
Maybe I"ll have to replace the cly head
Expert:  Donald replied 1 year ago.

I will agree, because I strongly believe that another cylinder head will resolve our problem.

Customer: replied 1 year ago.
ok thank you
Expert:  Donald replied 1 year ago.

You are very welcome! Find a good used one, and carry it to your local machine shop, to get it rebuilt.

Customer: replied 1 year ago.
sounds good I'm bewillerd to
Expert:  Donald replied 1 year ago.

My suggestions are based upon the fact that your engine ran great for the first 5 or 6 races. Since then, something have worn, or moved within your existing head.

Customer: replied 1 year ago.
I agree
Expert:  Donald replied 1 year ago.

Check eBay for a cylinder head, if you do not find one locally. You may save yourself some money ...

Customer: replied 1 year ago.
I have one here thank u
Expert:  Donald replied 1 year ago.

You are welcome!

Customer: replied 1 year ago.
good night
Expert:  Donald replied 1 year ago.

I hope you also have a good night. I do hope all goes well for you.