I mean, compression on my lawnmower is so high that I was inadvertently lifting the deck (suspended the entire mower!) by the rip cord on the compression stroke (and only on compression stroke, the motor spins freely on other strokes). Anyone else ever have that happen on a small engine? Just had to log in to post that lol
Compression that high?
- Thread starter jrustles
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What engine? Most of the Chinese knock-offs don't have the compression release mechanism that reputable brands like Briggs, Honda, Tecumseh, etc. all have.
Or the compression-release cam might be inoperative for some reason. Its a centrifugal mechanism that swings the compression release finger off the back side of the cam lobe once the engine comes up to speed, if its spring isn't returning it to place, you might not be getting compression release.
Or the compression-release cam might be inoperative for some reason. Its a centrifugal mechanism that swings the compression release finger off the back side of the cam lobe once the engine comes up to speed, if its spring isn't returning it to place, you might not be getting compression release.
It's a 5-6 yr old Tecumseh, broken in hard. It was my first engine purchase after learning about the motoman method.
The little 'valve bump' is still there, it's still a two stage resistance (the first one is strongest). It's just the funniest thing; each year the compression stroke puts up more and more resistance it seems. I went back out and could get the whole mower (was holding the handle side up) to suspend in the air for a good 1-2seconds before it bled down enough, to hit the valve bump! Kinda want to video it lol
Past two seasons been running SAE50 in it. No this isn't an endorsement for straight oils, that's just the oil I'm running in there. I was doing it because I have been experimenting with diesel, and got it up to about 70% before cold starts needed major assistance. The diesel never smoked until you released the run handle. I remember that with a significant amt of diesel in there, the mower would compression ignite after a certain amount of load. It's very loud on a flat head engine. And while I cringed when it happened, still felt emboldened enough to see if it would cause any damage. Nothing yet. It was just after discovering the compression ignition under load thing, that I dropped the Castrol Motorcycle SAE50 (SG? SH?) in there.
This happens on a cold engine. Was just tooling around with it, got it to fire on brake cleaner (tank is still empty) to verify that the ignition corrosion issue had not come back.
The little 'valve bump' is still there, it's still a two stage resistance (the first one is strongest). It's just the funniest thing; each year the compression stroke puts up more and more resistance it seems. I went back out and could get the whole mower (was holding the handle side up) to suspend in the air for a good 1-2seconds before it bled down enough, to hit the valve bump! Kinda want to video it lol
Past two seasons been running SAE50 in it. No this isn't an endorsement for straight oils, that's just the oil I'm running in there. I was doing it because I have been experimenting with diesel, and got it up to about 70% before cold starts needed major assistance. The diesel never smoked until you released the run handle. I remember that with a significant amt of diesel in there, the mower would compression ignite after a certain amount of load. It's very loud on a flat head engine. And while I cringed when it happened, still felt emboldened enough to see if it would cause any damage. Nothing yet. It was just after discovering the compression ignition under load thing, that I dropped the Castrol Motorcycle SAE50 (SG? SH?) in there.
This happens on a cold engine. Was just tooling around with it, got it to fire on brake cleaner (tank is still empty) to verify that the ignition corrosion issue had not come back.
Originally Posted By: AandPDan
Time to adjust the valves.
Just curious how you came to that conclusion?
It's a flat head btw with no provisions for adjustment.
Carbon is theoretically possible, but super-unlikely. It always gets hot and regularly see's WOT 'boosting' well over the governed speed. It runs great.
What speaks to me, is that leakdown rate with the thing hanging on it's own weight! gonna try and make a video doing that, and then it running
Time to adjust the valves.
Just curious how you came to that conclusion?
It's a flat head btw with no provisions for adjustment.
Carbon is theoretically possible, but super-unlikely. It always gets hot and regularly see's WOT 'boosting' well over the governed speed. It runs great.
What speaks to me, is that leakdown rate with the thing hanging on it's own weight! gonna try and make a video doing that, and then it running
@jrustles:
check your flywheel key to see if it has shifted somewhat.
I had similar issues with a Sears Craftsman 21" mower (older version B&S 5.00hp with sidedraft carb, circa late 90s) that roughly 3 out of every 5 pulls (cold, warm, etc. doesn't matter), the rope kicks back violently.
Checked the key has shifted quite a bit. Replaced it with a fresh new key and that solved the pulling issue (timing advanced too much to the point where the ignition timing worked against my pull-start...
Q.
check your flywheel key to see if it has shifted somewhat.
I had similar issues with a Sears Craftsman 21" mower (older version B&S 5.00hp with sidedraft carb, circa late 90s) that roughly 3 out of every 5 pulls (cold, warm, etc. doesn't matter), the rope kicks back violently.
Checked the key has shifted quite a bit. Replaced it with a fresh new key and that solved the pulling issue (timing advanced too much to the point where the ignition timing worked against my pull-start...
Q.
Originally Posted By: jrustles
Originally Posted By: AandPDan
Time to adjust the valves.
Just curious how you came to that conclusion?
It's a flat head btw with no provisions for adjustment.
If clearance increased you wouldn't hit the "bumps" on the compression release as hard. It's easy enough to check with just a feeler gauge. To adjust the valves you have to pull it and grind the seat to increase clearance or grind the tip of the valve stem to decrease it.
It's more common on an OHV engine but you do need to check it on a flat head too.
Originally Posted By: AandPDan
Time to adjust the valves.
Just curious how you came to that conclusion?
It's a flat head btw with no provisions for adjustment.
If clearance increased you wouldn't hit the "bumps" on the compression release as hard. It's easy enough to check with just a feeler gauge. To adjust the valves you have to pull it and grind the seat to increase clearance or grind the tip of the valve stem to decrease it.
It's more common on an OHV engine but you do need to check it on a flat head too.
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Originally Posted By: Quest
@jrustles:
check your flywheel key to see if it has shifted somewhat.
This!
@jrustles:
check your flywheel key to see if it has shifted somewhat.
This!
Originally Posted By: PhilsSmallEngine
Originally Posted By: Quest
@jrustles:
check your flywheel key to see if it has shifted somewhat.
This!
Easily tested- pull the spark plug wire. If it cranks normally, then the timing has shifted. If it cranks the same way with no source of ignition, then there's an issue with the compression release, or damage from abusing it with diesel oil in the fuel causing detonation.
Originally Posted By: Quest
@jrustles:
check your flywheel key to see if it has shifted somewhat.
This!
Easily tested- pull the spark plug wire. If it cranks normally, then the timing has shifted. If it cranks the same way with no source of ignition, then there's an issue with the compression release, or damage from abusing it with diesel oil in the fuel causing detonation.
Originally Posted By: Quest
@jrustles:
check your flywheel key to see if it has shifted somewhat.
I had similar issues with a Sears Craftsman 21" mower (older version B&S 5.00hp with sidedraft carb, circa late 90s) that roughly 3 out of every 5 pulls (cold, warm, etc. doesn't matter), the rope kicks back violently.
Checked the key has shifted quite a bit. Replaced it with a fresh new key and that solved the pulling issue (timing advanced too much to the point where the ignition timing worked against my pull-start...
+1! I had a 6hp Tecumseh in the late '90s that would do the exact same thing when the flywheel key had deformed and shifted timing. This was not a result of hitting anything and stopping the blade. The tecumseh just did that fairly often. I wasn't sad to see that engine go.
Q.
@jrustles:
check your flywheel key to see if it has shifted somewhat.
I had similar issues with a Sears Craftsman 21" mower (older version B&S 5.00hp with sidedraft carb, circa late 90s) that roughly 3 out of every 5 pulls (cold, warm, etc. doesn't matter), the rope kicks back violently.
Checked the key has shifted quite a bit. Replaced it with a fresh new key and that solved the pulling issue (timing advanced too much to the point where the ignition timing worked against my pull-start...
+1! I had a 6hp Tecumseh in the late '90s that would do the exact same thing when the flywheel key had deformed and shifted timing. This was not a result of hitting anything and stopping the blade. The tecumseh just did that fairly often. I wasn't sad to see that engine go.
Q.
Hey guys, sorry to disappoint but it's not ignition related in any way
the rotating assy is solid, nothing is mechanically wrong with the engine.
There is no fuel to prematurely ignite, the engine has not run on gasoline this season, bc I haven't gotten the first can yet! It's only been fired on a couple squirts of brake cleaner so far.
I grabbed these videos today in amongst the tree branch carnage from the ice storm. It's clearly not ignition of any sort, just good ol' compression! Enjoy
http://tinypic.com/player.php?v=2s6a5mr%3E&s=8
A couple of "wheelies" at first, then an actual lift & shift in the middle and then a total levitation towards the end
http://tinypic.com/player.php?v=2lxxc1h%3E&s=8
and a quick startup with a dry carb, no gas tank or fuel in the lines.. just a couple squirts of brake cleaner
There is no fuel to prematurely ignite, the engine has not run on gasoline this season, bc I haven't gotten the first can yet! It's only been fired on a couple squirts of brake cleaner so far.
I grabbed these videos today in amongst the tree branch carnage from the ice storm. It's clearly not ignition of any sort, just good ol' compression! Enjoy
http://tinypic.com/player.php?v=2s6a5mr%3E&s=8
A couple of "wheelies" at first, then an actual lift & shift in the middle and then a total levitation towards the end
http://tinypic.com/player.php?v=2lxxc1h%3E&s=8
and a quick startup with a dry carb, no gas tank or fuel in the lines.. just a couple squirts of brake cleaner
Pull the spark plug and see iff it still has as much "compression". I bet there is carbon on the head above a valve, causing more resistance when the valve opens.
Originally Posted By: datech
Originally Posted By: AandPDan
Time to adjust the valves.
Maybe it is carbon build up raising the compression level.
This. You have been running a gas engine on a ?70% diesel blend?
you probably have a bunch of carbon all over the piston top. The compression is probably high from that. Pull the head and clean it.
Make sure the muffler is not plugged with carbon too.
Originally Posted By: AandPDan
Time to adjust the valves.
Maybe it is carbon build up raising the compression level.
This. You have been running a gas engine on a ?70% diesel blend?
you probably have a bunch of carbon all over the piston top. The compression is probably high from that. Pull the head and clean it.
Make sure the muffler is not plugged with carbon too.
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Originally Posted By: asand1
Pull the spark plug and see iff it still has as much "compression". I bet there is carbon on the head above a valve, causing more resistance when the valve opens.
With no plug in, of course it doesn't, spins free (and makes a funny gasping 'wwahwahwah' noise). Is it possible for carbon to buildup enough to impede a valve, in the time fame of three strokes..before the valve again travels it's entire path.. does that happen? Aside from all of that, though.. cylinder pressure leakdown decreases with head carbon buildup?
Originally Posted By: spasm3
You have been running a gas engine on a ?70% diesel blend?
you probably have a bunch of carbon all over the piston top.
Nahhhh! lol I promise, it's not carbon
That diesel run was a short-term experiment, and as I noted earlier, it did burn very cleanly in a HCSI mode, as noted by the same usual non-odourous exhaust, lack of smoke or soot on the muffler and clean plug; areas that would be notably sooty with poor quality combustion. Only time I could get it to blow a little diesel smoke was when disengaging the run handle just enough to cut the spark, but not enough to hit the brake, if you know what I mean! Mmm smelled like truckin'. Otherwise, no smoke faint smell, proper combustion.
I appreciate the ideas, but I'm not seeking diagnosis. There is nothing wrong with the engine, it runs incredibly. Exhaust smells very 'clean' as far as uncatalysed small engine exhaust goes, it has excellent stall resistance, esp with that diesel mix because it would compression ignite under those loads! Nevertheless, it runs regular gas 98% of the time, and has never knocked.
The engine's had a [excessively] good start to it's service life with about 10 initial oil changes in about 10hours, broke in hard, has been filled with a variety of oils from Esso XD-3 0w40 to the old Castrol Motorcycle mineral SAE50 in there now. Doesn't burn oil. It used to have a piece of dental floss tied to the throttle that I'd yank as a preemptive 'booster' for heavy mulch ops over wet bulky grass, a highly engineered setup
It's been kerosene flushed and drained at all angles to wash the break in sparklies away. Aside from being covered in winter salt dust, that engine's service plan has been BITOG neurosis tier
Anyway, this isn't normally a kind of post I'd make, but had just felt so compelled yesterday when what had happened made me chuckle and want to share.
Pull the spark plug and see iff it still has as much "compression". I bet there is carbon on the head above a valve, causing more resistance when the valve opens.
With no plug in, of course it doesn't, spins free (and makes a funny gasping 'wwahwahwah' noise). Is it possible for carbon to buildup enough to impede a valve, in the time fame of three strokes..before the valve again travels it's entire path.. does that happen? Aside from all of that, though.. cylinder pressure leakdown decreases with head carbon buildup?
Originally Posted By: spasm3
You have been running a gas engine on a ?70% diesel blend?
you probably have a bunch of carbon all over the piston top.
Nahhhh! lol I promise, it's not carbon
That diesel run was a short-term experiment, and as I noted earlier, it did burn very cleanly in a HCSI mode, as noted by the same usual non-odourous exhaust, lack of smoke or soot on the muffler and clean plug; areas that would be notably sooty with poor quality combustion. Only time I could get it to blow a little diesel smoke was when disengaging the run handle just enough to cut the spark, but not enough to hit the brake, if you know what I mean! Mmm smelled like truckin'. Otherwise, no smoke faint smell, proper combustion.
I appreciate the ideas, but I'm not seeking diagnosis. There is nothing wrong with the engine, it runs incredibly. Exhaust smells very 'clean' as far as uncatalysed small engine exhaust goes, it has excellent stall resistance, esp with that diesel mix because it would compression ignite under those loads! Nevertheless, it runs regular gas 98% of the time, and has never knocked.
The engine's had a [excessively] good start to it's service life with about 10 initial oil changes in about 10hours, broke in hard, has been filled with a variety of oils from Esso XD-3 0w40 to the old Castrol Motorcycle mineral SAE50 in there now. Doesn't burn oil. It used to have a piece of dental floss tied to the throttle that I'd yank as a preemptive 'booster' for heavy mulch ops over wet bulky grass, a highly engineered setup
Anyway, this isn't normally a kind of post I'd make, but had just felt so compelled yesterday when what had happened made me chuckle and want to share.
It is possible to have enough carbon built up in the head that the valve hits it. The carbon does not remain compressed though. It is spongy enough that the valve hits each time and encounters resistance to movement.
The reason I asked about the spark plug is because resistance in the absence of a plug would rule out compression increase. You never stated that removed the plug, an "of course" was not warranted, and a bit insulting.
Yes carbon build up would increase compression ratio. And leak down would then take longer.
The reason I asked about the spark plug is because resistance in the absence of a plug would rule out compression increase. You never stated that removed the plug, an "of course" was not warranted, and a bit insulting.
Yes carbon build up would increase compression ratio. And leak down would then take longer.
Bottom line is this engine has a compression release, and you don't have more compression than you did, especially at starting rpm.
Originally Posted By: asand1
Bottom line is this engine has a compression release, and you don't have more compression than you did, especially at starting rpm.
You're right, compression has always felt high, even the first year I had it- and it's been getting better- which according to you, could only be carbon, springy gaseous compressable carbon lol.
I know why you asked, the plug was out @ end of last year when it flooded because of a no-spark condition which has been rectified by removing the coil, sanding the grounding mounting points and reinstalling. The engine was spun (freely) w/o the plug to dry up the cylinder. Any resistance would be an instant red flag during that time, of course.
If it is carbon, then the ring leakdown before the cam compression release 'bump' is a new way to improve engine performance and I should tell engine builders and servicemen worldwide!
But seriously, there is nothing wrong with the engine. Please, just accept that or move on. Again, I appreciate you trying to help? (or hassling me trying to debunk something for some reason, not sure).
By time I'm done addressing each and every one of these 'concerns' I'd have done told my life story!! sheesh never imagined that excellent sealing rings would garner such offense!
Bottom line is this engine has a compression release, and you don't have more compression than you did, especially at starting rpm.
You're right, compression has always felt high, even the first year I had it- and it's been getting better- which according to you, could only be carbon, springy gaseous compressable carbon lol.
I know why you asked, the plug was out @ end of last year when it flooded because of a no-spark condition which has been rectified by removing the coil, sanding the grounding mounting points and reinstalling. The engine was spun (freely) w/o the plug to dry up the cylinder. Any resistance would be an instant red flag during that time, of course.
If it is carbon, then the ring leakdown before the cam compression release 'bump' is a new way to improve engine performance and I should tell engine builders and servicemen worldwide!
But seriously, there is nothing wrong with the engine. Please, just accept that or move on. Again, I appreciate you trying to help? (or hassling me trying to debunk something for some reason, not sure).
By time I'm done addressing each and every one of these 'concerns' I'd have done told my life story!! sheesh never imagined that excellent sealing rings would garner such offense!
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