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James W
James W, Small Engine Troubleshooting Expert
Category: Small Engine
Satisfied Customers: 3708
Experience:  7 years as Mechanic & Parts Manager for Brother who has Owned Lawn & Garden Repair shop for 35 years
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I have briggs and stratton over head valve engine bent a push

Customer Question

I have briggs and stratton over head valve engine bent a push rod probable causes and can I just replace the push rods with out taking the whole thing apart
Submitted: 6 years ago.
Category: Small Engine
Expert:  James W replied 6 years ago.

James W :

Greetings, My name is James W, and I am here to help the best I can. My goal is 100% satisfaction. Let's get started.

James W :

To help you out, I have supplied you with a complete service manual for repairing your engine

James W :

There are a couple reasons why a push rod will bend

James W :

The absolute most common reason for one bending is an engine that is overheating.

James W :

What could cause the overheating problem?

Overheating can be attributed to two things something getting to hot or something not getting cooled properly.

Lets take the situations that would cause something to get too hot first.

Engines can create extra heat by having the engine run too lean....(Not getting enough fuel) Fuel is not only used to create the power in an engine but it is also used as a coolant in the combustion chamber. If it runs too lean, then the explosions will create more heat and then there is also not enough fuel to help cool the engine.

What would cause the engine to run too lean?

As engines sit or get older, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems.

Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.

More than 70% of all of our repairs in our lawn mower business are due to this same issue. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carb. It Must be removed from the engine, cleaned very well, blown out with compressed air and reassembled using a NEW carburetor rebuild kit. ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carb too. Dirt and water from a dirty fuel tank will also plug up the carb. Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carb kit.

Ok now lets see what could cause the engine to have insufficient cooling.

When small engines run, they build up heat as a natural byproduct of combustion.

Just as a wood burning stove gives off heat so does a combustion engine. Different fuels will produce different amounts of heat. Coal for instance burns much hotter than wood.....a hardwood such as oak or hickory burns much hotter than softwoods such as soft maple of cottonwood. The same can be said for gasoline. 87 octane gives off much more heat than 89 octane of premium. That is because 87 octane explodes and all of the heat is transferred to the piston in one very fast burst. It cannot be transferred through the piston and cylinder to the air fins where the air from the cooling fan takes it away fast enough to keep the engine running as cool as we would like. On the other hand, mid-grad 89 octane and premium fuels do not explode...they burn in a much slower manner and the added time aids the engine in cooling., so the engine runs much cooler. This is due to the antiknock compounds that have been added to the fuel. The tiit-knock compounds job is to slow the burning process and to eliminate the explosions that result in the knock (or pre-ignition) that occurs with regular gas. The problems we are having with the gas these days is that they keep making it cheaper and cheaper by not adding as many additives as they one did. These additives are very expensive.

So as a conclusion, we do not recommend using 87 octane in ANY SMALL ENGINE. We would prefer that only good Brand (NOT CHEAP DISCOUNT STATION) gasoline is used in all 4-cycle engines and Premium MUST be used in ALL 2-cycle engines.

Another situation that causes the engine not to cool well is that grass builds up under the engine cover....we call this the birds nest affect.....When grass is built up under the shroud or cover as we call it, it blocks the flow of air around the cylinder and block of the engine. This prevent the engine from cooling because it cannot take away the heat that was created during combustion. In many cases this grass build-up gets so hot that it can even create a fire under the cover.

James W :

Instructions for installing the push rods the easist way stat about on chapter 100 of the service manual

James W :

Also, read about the need to adjust the valv gap

James W :

the engine has a compression release for starting, but misadjusted the compression release does not operate at all. this can also bend push rods

James W :

if the head has warped the push rods may warp again

James W :

the only way to fix that is to replace the head

JACUSTOMER-3ig5it7h- :

the carb was all gummed up put a new kit in so that was probaly the reason it got hot it was missing some when the last time I ran it and it was running when I shut it off when I went back the next time to cut grass no start my next question is is it advisable to put new push rods in with out tearing the whole thing down it still has good compression can't hear any leaks coming from the head does not have many hrs. on it

James W :

The push rods are not that expensive

James W :

there is no reason to perform a whole teardown if the compression is good

James W :

but you will adjust the valve lap to specs and do that EVERY YEar

James W :

Did you have a chance to download the service manual

James W :

??

JACUSTOMER-3ig5it7h- :

thanks the shop that I had put the the engine in didn't tell me that and no I have not yet but will

James W :

While you have the head off, remove all the carbon as per page 11

James W :

Most owners manuals are wrong on purpose

James W :

this is calle planned obsolecence

James W :

they want you to buy a new engine every 7 years

James W :

You can make it last 20 to 25 years with proper care

JACUSTOMER-3ig5it7h- :

ya I just bought that one 3 years ago

James W :

OK, when new, change oil and filter after first 2 hours to get put together grit out

James W :

then after next five hours change oil and filter again

James W :

then after every 15 or so hours NOT after 50 hours.

James W :

You will notive that the same engine may be used for various purposes, not just lawn tractors

James W :

they manuals will always say "More often if used in dirty or dusty environments".

James W :

But, there is not worse environment than or a riding lawn mower, so you MUST change oil often

James W :

ALSO old gas has particles of gum and varnish in it that changes to carbon burnt nodules that damage the cylinder, then get mixed into the oil

James W :

these nodules then wear out the internal parts that touch oil unless the oil change more often

James W :

change air filters just as often as the oil and oil filters to keep the dirt out and the oil clean

James W :

Get on a cycle of about every 15 hours

James W :

I will be available for additional follow-up questions. If my answers have not been acceptable, please let me know what more I can do. I will be notified via email of your responses even after you Hit ACCEPT.

JACUSTOMER-3ig5it7h- :

thanks again I don't think I will be returning to that repair shop again they were suposse to to have put a carb kit in last year and i have chanaged the fuel filter regular

Expert:  James W replied 6 years ago.
I have converted the question to Q&A Mode rather than chat. I will be available for additional follow-up questions. If my answers have not been acceptable, please let me know what more I can do. I will be notified via email of your responses even after you Hit ACCEPT.