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Donald
Donald, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1797
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: 11 months ago.
Category: Small Engine
Expert:  Donald replied 11 months ago.

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

Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
Some times it will go two or three or 7or 8
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
No laps
Customer: replied 11 months ago.
u still there
Expert:  Donald replied 11 months ago.

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

Expert:  Donald replied 11 months 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 11 months ago.
they are working fine when it runs it runs strong
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
six or seven
Expert:  Donald replied 11 months ago.

Are they OEM rocker arms?

Customer: replied 11 months ago.
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
mostly intake
Expert:  Donald replied 11 months ago.

Are you using a stock cam gear in your engine?

Customer: replied 11 months ago.
No it is a big cam
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
No it run 5 or six races ran great run up front every week
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
yup
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
ok
Expert:  Donald replied 11 months 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 11 months ago.

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

Expert:  Donald replied 11 months 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 11 months ago.
Key way is good springs they are dubble springs
Customer: replied 11 months ago.
they look good
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
ya
Expert:  Donald replied 11 months 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 11 months ago.
Have done that and no ping marks. Could the valve guides move up and do that?
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
How do you check them
Expert:  Donald replied 11 months ago.

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

Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months 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 11 months 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 11 months ago.

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

Customer: replied 11 months ago.
they seem to be good
Expert:  Donald replied 11 months 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 11 months ago.
the intake valve is a longer valve
Expert:  Donald replied 11 months ago.

Thank you for checking.

Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
it is sorry I did not see u got back to me
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
shoot
Expert:  Donald replied 11 months 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 11 months ago.
I have had the head off to have seat replaced and found no problem with it at the machine shop
Customer: replied 11 months ago.
Maybe I"ll have to replace the cly head
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
ok thank you
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
sounds good I'm bewillerd to
Expert:  Donald replied 11 months 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 11 months ago.
I agree
Expert:  Donald replied 11 months ago.

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

Customer: replied 11 months ago.
I have one here thank u
Expert:  Donald replied 11 months ago.

You are welcome!

Customer: replied 11 months ago.
good night
Expert:  Donald replied 11 months ago.

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