bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
Guides can not be replaced they are cast in as happens on most mower engines now days
Guide replacement rarely happens on any vehicle now days most auto shops will sleeve the valve
You are equating water cooled horizontal shaft engines with air cooled vertical shaft engines and they are cheese & chalk
To replace guides now days you need to machine out the guide and guides are very very hard then collapse the reminant into the hole
If you try to push it out you will destroy the head
Even then you will have to fit an oversized guide then real it out to give proper clearances for the valve stem
Valve stems are soft now days so they wear & guides don't .
Modern emission laws have air cooled engines running way too hot and I would bet your engine is running that tiny bit hotter
Down here mowers are not as strictly controlled as in the USA so it is legal for me to ream out main jets a tiny bit so the engine runs a little cooler and I have needed to do this on a lot of engines.
The 7000 series are really bad , on the B & S engines with 2 barrel carbs I toss the small jet & use 2 large ones
The other thing I do on engines that are cooking is to double the magneto coil gap,
This retards the spark a poofteenth which causes the engine to run a tad less hot.
You can not do a reliable plug chop on a mower engine because of the fuel solenoid but when I change the timing I check the spark plugs , if they are sooty then I have gone too far .
Remember mowers have fixed timing unless that are EFI models so the timing is never 100% accurate.
Several companies tried to bring invariable ignition timing and when it worked it was amazing but when these units failed it was a disaster but I really think the reason was cost as all of them used a triple wound coil.
I have a motorcycle with a flywheel magneto ( Yamaha SR 500 ) and the magneto + trigger unit+ flywheel need to be replaced as a matched set which is $ 1600 ( AUS ) and that is more than most Americans want to pay for a complete engine
The usual test for guides is to rev then decelerate the engine which on a governed engine will require you to work the governor arm.
So you go from wide ope throttle then shut it down completely
Smokes on accleleration = rings
Smokes on deceleration = valves
You have to be careful doing this because most engines will happily rev up to 5000+ rpm very quickly and at around that speed most pistons will depart from the end of the con rods
In nearly 12 years I have never needed to replace valve stem seals , most engines only have one on the inlet by the way , except in cases where the engine has well & truely cooked and needed new rings .
Some of my customers who had a lot of problems with smoking on start up were causing this to happen by idling the engines down before they shut off
Again a water cooled engine practice that is very bad for aircooled engines as the heat removal is exponential to the engine speed and heat generated is linear with engine speed
So in that minute or so when they thought they were "cooling" the engine they were in fact baking the engine and in particular cooking the heads
This is assuming your engine is good and the reason for replacing both coils was not some sort of catastrophic engine failure as you have not provided any back story
Guide replacement rarely happens on any vehicle now days most auto shops will sleeve the valve
You are equating water cooled horizontal shaft engines with air cooled vertical shaft engines and they are cheese & chalk
To replace guides now days you need to machine out the guide and guides are very very hard then collapse the reminant into the hole
If you try to push it out you will destroy the head
Even then you will have to fit an oversized guide then real it out to give proper clearances for the valve stem
Valve stems are soft now days so they wear & guides don't .
Modern emission laws have air cooled engines running way too hot and I would bet your engine is running that tiny bit hotter
Down here mowers are not as strictly controlled as in the USA so it is legal for me to ream out main jets a tiny bit so the engine runs a little cooler and I have needed to do this on a lot of engines.
The 7000 series are really bad , on the B & S engines with 2 barrel carbs I toss the small jet & use 2 large ones
The other thing I do on engines that are cooking is to double the magneto coil gap,
This retards the spark a poofteenth which causes the engine to run a tad less hot.
You can not do a reliable plug chop on a mower engine because of the fuel solenoid but when I change the timing I check the spark plugs , if they are sooty then I have gone too far .
Remember mowers have fixed timing unless that are EFI models so the timing is never 100% accurate.
Several companies tried to bring invariable ignition timing and when it worked it was amazing but when these units failed it was a disaster but I really think the reason was cost as all of them used a triple wound coil.
I have a motorcycle with a flywheel magneto ( Yamaha SR 500 ) and the magneto + trigger unit+ flywheel need to be replaced as a matched set which is $ 1600 ( AUS ) and that is more than most Americans want to pay for a complete engine
The usual test for guides is to rev then decelerate the engine which on a governed engine will require you to work the governor arm.
So you go from wide ope throttle then shut it down completely
Smokes on accleleration = rings
Smokes on deceleration = valves
You have to be careful doing this because most engines will happily rev up to 5000+ rpm very quickly and at around that speed most pistons will depart from the end of the con rods
In nearly 12 years I have never needed to replace valve stem seals , most engines only have one on the inlet by the way , except in cases where the engine has well & truely cooked and needed new rings .
Some of my customers who had a lot of problems with smoking on start up were causing this to happen by idling the engines down before they shut off
Again a water cooled engine practice that is very bad for aircooled engines as the heat removal is exponential to the engine speed and heat generated is linear with engine speed
So in that minute or so when they thought they were "cooling" the engine they were in fact baking the engine and in particular cooking the heads
This is assuming your engine is good and the reason for replacing both coils was not some sort of catastrophic engine failure as you have not provided any back story