[Surfincr]

So after using the brush hog this weekend on my 6.6 l8 i am getting the feeling she needs a rebuild. i've noticed with the 40" commercial she'll do ok with short grass but if it gets thick or tall it'll bog right down. with the brush hog it turns with a little stiffness but does not appear to have a bent blade but the L8 when trying to start the pto with kill the tractor. i found giving it a little throttle and a lot of patience i can get it going and it does ok. so is this normal for the 6.6 or is it time for a rebuild?

if its rebuild time is it worth upgrading to the 7.6 and if so what parts do it need?

my thought is if it needs it why not rebuild both gravelys and see about investing in a powder coating system for the rebuild.

 

[CTPhil]

I'd start with a compression test, that should tell a lot.

 

[Surfincr]

I'd start with a compression test, that should tell a lot.

i have the compression tester but i need the correct adapter, any good places to find the correct one? (i think when you stopped by to look at the l's we talked about this then too, but i dont remember the answer)

 

[beaner2u]

A thirty inch mower should not have any stiffness, you should be able to tip the mower up and spin the blade and have it coast for a turn or two.

When you hand crank your engine over do you encounter much compression? It should not be easy to turn over buy hand. A loss of compression is a loss of horsepower.

The 7.6 cylinder is stronger at the top, that is the real advantage of the 7.6, and the bottom cases do have some additional reinforcing at the exhaust cam and cylinder mounting bolts, the carburetor venturi was changed from a 17mm to an 18mm, the flywheels and connecting rod are a few ounces heavier, but the horsepower gain is a sales tool. The higher horsepower rating was obtained mostly by over-reving the engine for testing.

The real horsepower change was between the 5hp and the 6.6hp, the cams changed both profiles and timing, the carburetor went from a 15mm venturi to 17mm, the high pressure oil pump, and the stronger connecting rod with oiler squirt holes.

Roger.

 

[CADplans]

Does a manometer test work on a Gravely engine? :dunno:

 

[beaner2u]

CAD,

A fair question, but Gravely never gave us any specs to work with that would be pertinent to a Gravely built engine. Let us remember that the bottom cases of a Gravely built engine are open to the chassis of the tractor.

Sure you could block off the advance casting and plug the oil filler hole, but there is a whole different volume of air in the combined engine/chassis of a Gravely compared to the sealed engine cases of a Kohler.

If you rebuild a Gravely engine, block off the advance casting, plug the oil fill hole, check out all oil seals on the chassis, we will wait for your test results so that we can check our engines. :-}

Roger,

 

[CADplans]

Roger, LOL!! :ROF

One more reason I run the Kohler powered 2-wheelers!!

I had not thought about the open engine.

:fing32:

 

[CTPhil]

i have the compression tester but i need the correct adapter, any good places to find the correct one? (i think when you stopped by to look at the l's we talked about this then too, but i dont remember the answer)

I got mine here.

 

[rscurtis]

Check the valve clearance before you do anything. Unleaded gas will cause valve seat recession on these engines.

 

[Surfincr]

I got mine here.

Thanks Phil, i was trying to figure this out yesterday is it this one i need?

7/8" Flat Seat x 14mm Tapered Seat Sparkplug Adapter
- 1" Hex Diameter
- 7/8" Thread Diameter (Outside)
- 14mm Thread (Inside)
- Fits most engines built between 1925-1939


last time i had to use the pull strap there was a decent amount of compression. i'll have to make my way out tonight to check by hand

 

[cmeyers77]

If you don't already have a service manual download one from the the gravely tractor club website, they are very helpful when needing specifications for adjustments.

Things that will cause your tractor to loose power

Dirty air cleaner
Poorly adjusted/worn carburetor
Poorly adjusted/worn magneto, check/replace points and condenser. Check timing and spark strength, magnetos can become weak over time
Worn spark plug
Valve adjustment
A governor not adjusted properly may give the illusion of power loss

I was once of the belief that a Gravely L Engine was not powerful enough to power a 40" mower, turns out I was wrong. Turns out what I had was a worn out machine. Valves were out if adjustment and needed a regrind, as was the carburetor. The timing was wrong and the points were shot. After I rebuilt the carburetor, a later one with the larger Venturi, complete with new throttle bushings, set the valves correctly and properly adjusted the governor it performed like no other Gravely L I have ever operated. If you have good compression then the rest is easy, if you are low on compression and the engine is not blowing smoke I would suspect the valves are in need of work, weather they just need adjustment or a regrind. If you end up taking the head off the Jug inspect the cylinder for cracks as well as a worn piston, large gap between the piston and cylinder on the exhaust side. Gravely engines are low compassion engines so a little bit of compression loss can show up as a bigger power loss then other higher compression engines.

Good luck
Corey



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[cmeyers77]

Also as someone ales has mentioned check for smooth operation if the mower deck, I know after if rebuilt my 40" mower deck the tractor seemed to have an easier time powering it.


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[Richard-tx]

Lapping the valves is NOT the same as grinding. Never lap a worn valve. Get it ground.

 

[cmeyers77]

Lapping the valves is NOT the same as grinding. Never lap a worn valve. Get it ground.

Very true, I would think in most cases if the valves need to be reground then the cylinder needs work too, it just depends on how hard the engine has been worked and or if it has sat for long periods with a valve open.


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[CTPhil]

Thanks Phil, i was trying to figure this out yesterday is it this one i need?

7/8" Flat Seat x 14mm Tapered Seat Sparkplug Adapter
- 1" Hex Diameter
- 7/8" Thread Diameter (Outside)
- 14mm Thread (Inside)
- Fits most engines built between 1925-1939

I believe that's it. As long as your in it for shipping, buy several. As you get older you'll forget where you left them, LOL.

 

[Surfincr]

If you don't already have a service manual download one from the the gravely tractor club website, they are very helpful when needing specifications for adjustments.

Things that will cause your tractor to loose power

Dirty air cleaner
Poorly adjusted/worn carburetor
Poorly adjusted/worn magneto, check/replace points and condenser. Check timing and spark strength, magnetos can become weak over time
Worn spark plug
Valve adjustment
A governor not adjusted properly may give the illusion of power loss


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i probably should have added so far with the tractor i've done the following:
replaced the air cleaner
rebuilt the carb
new spark plug
adjusted the governor

on one of the tractors i know i replaced the points and condensor i think it was the l8 as well, now i have to check.



not sure if it helps i forgot to mention after i was running the brush hog it did not want to shut off and started dieseling. i pulled the spark plug wire and she still went for another 30 seconds

 

[Surfincr]

I believe that's it. As long as your in it for shipping, buy several. As you get older you'll forget where you left them, LOL.

i've already started getting duplicates of a lot of my tools since half the time i cant remember which project i was using them on

 

[cmeyers77]

not sure if it helps i forgot to mention after i was running the brush hog it did not want to shut off and started dieseling. i pulled the spark plug wire and she still went for another 30 seconds

Dieseling, or run-on is a good indication of running too hot and or very poor timing. If the fuel mixture is too rich and or the timing is too far out, advanced, run on can happen. When an air cooled engine is running hot a loss of power is a given. If the mixture is too lean the engine will run hotter. It sounds like you have a lot going on with this engine, does the power loss occur over time, meaning the longer you use it the more you notice the power drops?




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[Surfincr]

Dieseling, or run-on is a good indication of running too hot and or very poor timing. If the fuel mixture is too rich and or the timing is too far out, advanced, run on can happen. When an air cooled engine is running hot a loss of power is a given. If the mixture is too lean the engine will run hotter. It sounds like you have a lot going on with this engine, does the power loss occur over time, meaning the longer you use it the more you notice the power drops?

This was actually this first time it has happened to me with the engine experiencing run on. the loss of power i find to be the entire time i use it. i'll see to checking the timing when i have some down time and see about pulling the carb apart again.

 

[cmeyers77]

This was actually this first time it has happened to me with the engine experiencing run on. the loss of power i find to be the entire time i use it. i'll see to checking the timing when i have some down time and see about pulling the carb apart again.

It really can be a pain to troubleshoot engine problems, as far as the ignition from what I've read magnetos can loose their magic over time, coils can crap out as they get hot. To me if the engine starts up easily and does not consume oil then the core of it is good, you may have a burned exhaust valve or a leaky head gasket. The head is easy enough to remove for an inspection of the the piston and valves as well as to see if any cracks are present.


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