# Over heating Muffler



## Spit (Nov 3, 2006)

I am working a Craftsman 5hp (tecumseh engine) it's a pure rear bagger (no optional side chute it's grey with a red and balck engine shroud I think it's under 10 years old..sorry no model numbers at this time... I picked it up on the side of the road...turns out the carb was missing, had I noticed that I robably wouldn't have bothered. Anyway I got a carb off of a another Craftsman mower and installed it.. 

The engine has good compression and spark and is running with the replacement carb. I cut my grass with it last night. However it seems to run too fast (RPM) and it won't go to low speed... This particular engine has a high low setting lever that seems to work off of the governnor. The carb that I put on came off a Craftsman with the same type of 2 speed lever. It seems to be the standard Craftsman/Tecumseh non-adjustable carb..It has a primer bulb on the side of it and just a single throttle shaft..no seperate choke..no high speed and low speed needles just one screw to adjust the idle speed.

I tired to mimic the hook-up on the linkages to be 


Any way the muffler appears to be getting way too hot...hot enough to melt a hole through the belt shield for the front wheel self propelled system. The muffler sits right above the shield 2 inches or so off of it. Am I running it too fast and overheating the muffler? do I have an exhaust valve problem?
Maybe I have the governor linkage hooked up wrong. Funny thing is that the belt shield had a baseball sized melt/deformitiy in it when I picked it up...so what ever was wrong seems to have been wrong before I worked on it

I know I'm not giving you much to work on but if anyone has an idea I would love to hear it.

Spit


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## jsouth (Jan 31, 2008)

How does the air filter look,was it dirty when you pick it up.How about the plug did it have black soot on the end of the plug.Could have carbon built up in the combustion chamber,causing the muffler to get hot.May have to take the head off and clean the chamber.Hope this helps.

Jerry


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## LowRider (Dec 23, 2008)

Correct RPM is essential to a good running engine. Unless you post numbers off the engine i think its really a guess in the park on the muffler just yet. What does the engine idle at and what is the maximum rpm at full throttle? Don't say it sounds good cause that's no help, get a tachometer and check. A different carb off an identical engine could be the problem if it runs rich which isn't always good. Post the engine code and someone here can help you and maybe find out if the carb on it is the right one. I'm not sure but there is probably numbers on the carb itself also that can be checked.


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## 30yearTech (Sep 14, 2006)

It's also possible that there is an exhaust leak in the muffler, mounting gasket or head gasket, allowing a hot discharge to be directed at the belt cover.


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## Rentahusband (Aug 25, 2008)

Sometimes one mans junk is anothers treasure.This might just be pure junk. I would make sure the RPMs are within range. Carb may not be properly set up for this engine.
Dean


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## geogrubb (Jul 28, 2006)

I vote for leaking head gasket. Have a good one. Geo


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## Spit (Nov 3, 2006)

*Model number info attached.*

This is a Craftsman Mower model 917.372480 with a Craftsman engine model number is 143.424152 which is a Tecumseh # TVS120-63911H.

I rebuilt the carb last night... installed a new internal intake tube and both o-rings, inlet seat and needle, and bowl o-ring.I also replaced the intake manifold gasket (where it mounts to the intake port on the side of the engine.
I had been experiencing gas leaking from the air filter that's all fixed now.

It seems like I still don't have a low speed...engine seems to run at the same speed regardless of high-low setting lever. I rechecked both of the carb linkages to the governor and feel that those are in the right places top solid link goes to throttle link bottom 2 piece link spring and solid link to a lever on the speed control plate....I'm not sure that the spring on the one linkage has been stretched a little too much...and the the solid rod linkage doesn't have a little bit of a bend that it shouldn't have at the end where it connects to the engine governor? Not sure how much that would affect engine speed. 
. 

One thing I am not clear on is how the high-low carb control plate is aligned with the carb below it. I saw some instructions in the service manual I have but I'm not sure which type of control plate I have. There are 2 adjustment screws on this plate.. I did back one of them way off and it seemed to slow down the engine..I do think the RPMs were too high. Can anyone tell me what the 2 adjustments screws control and which is which

I did take the head off last night and cleaned it and the piston head of carbon. I did think that the bolts holding the head on were not very tight. The head gasket was completely intact..but I did think that the bolts should have been torqued tighter..does anyone know the torque specs?

I wasn't able to run the mower for very long after all of my adjustments...it was just too late at night for the neighbors etc. It did seem to start right up on the 1st pull I'm just not sure if the overheating is done or not.

any comments or ideas on things for me to check are greatly appreciated.


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## Spit (Nov 3, 2006)

I think I have the problem resolved. It looks like my problem was caused by the governor. I don't have a tach but I'd guess the engine was running much faster than it should have been. I was playing around with the linkage rods that attach to the governor arm. It just didn't seem like the governor was working right.. then I loosened the screw that attaches the governor arm to the side of the engine, it flipped around, I flipped it back and re-tightened the screw and the engine stopped racing. I have distinct low and high speeds..not 100% sure what I did but it seems to be working now. 

I used a little piece of sheet metal and some pop-rivets and made a patch for the hole that the muffler caused in the belt guard. It actually looks fairly decent.


spit









side of the engine


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## AW_3_3 (Jun 27, 2009)

The normal RPM of lawnmower engines is around 3600RPM. It's pretty much the defacto across the board, for briggs, tecumseh, honda, chinese engines.... Glad its working. For me, I can tell if its running too fast, because I want to run away and hide, it sounds like its going to explode... Haha


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## 30yearTech (Sep 14, 2006)

AW_3_3 said:


> The normal RPM of lawnmower engines is around 3600RPM. It's pretty much the defacto across the board, for briggs, tecumseh, honda, chinese engines.... Glad its working. For me, I can tell if its running too fast, because I want to run away and hide, it sounds like its going to explode... Haha


Maximum rpm's on lawn mowers are determined by the length of the blade. Maximum rpm's of the engine itself if determined by it's design and construction. Many models of engines will run in excess of 4,000 rpms with no problems at all, this would be way too fast for a lawnmower application, as is 3,600. Most mowers will fall into the 2,800 - 3,200 range, unless they utilize a fairly short blade.


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## geogrubb (Jul 28, 2006)

Sorry, I only do this because:

Formula for mower blade speed
RPM's on lawnmowers are actually set for maximum blade tip speed of 19,000 feet per second, and of course should not exceed the engine mfg specs. for the engine.


To calculate blade tip speed you would have to take the length of the blade say 21" and multiply that by the engine or spindle RPM's say 3200 then take the result (for this example 67200) then multiply this by 3.14 (pie) (211008) and then divide by 12 (inches in a foot) = 17,584 Feet Per Minute.

The maximum blade tip speed as set by government standards is listed as 19,000 feet per minute.

Blade length X RPM's X 3.14 / 12 = Blade Tip Speed in Feet Per Minute.

If you want to figure out maximum rpm's based on blade size then you could do this

19000 (divided by) the result of (Blade length X 3.14 (divided by) 12) = Max RPM's

Example:
For a 21" blade the formula would look like this:
19000 / ((21 * 3.14) / 12) = 3457
It carries out several decimal points, but you can just round down for the maximum blade tip speed.

The maximum RPM's you should set a 22" mower for is 3300.


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## Spit (Nov 3, 2006)

Geoerge, 30 Year & others

Thanks for the great information. I love having the formulas etc. for how things are calculated. Is there somewhere I can get a cheap tachometer. 
Seems like back in the day the techs at a shop I worked at had a small pocket sized gizmo with a wire that extended out of it...they would place it on the top shroud of the engine? and they could determine RPM? Sound right? Is there somewhere I could one?

Spit


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## geogrubb (Jul 28, 2006)

The item you refer to is Tecumseh Part# 670156 it is a Treysit made in Germany sells for about $10-$12. Have a good one. Geo


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## 30yearTech (Sep 14, 2006)

Briggs has one also called a Vibratach part no. 19200, but it's more expensive at around $30.00


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