bertsmobile1
Lawn Royalty
- Joined
- Nov 29, 2014
- Threads
- 64
- Messages
- 24,705
Firstly and this is important,
IT IS NOT A SCRATCH.
Scratches go along the bore not around it
It is a corrosion pit
It will be a lot deeper than it looks & feels but most importantly the rings will also have been damaged .
And this is verified by the big difference in the wet & dry compression readings
The piston grooves could also been damaged , they usually are .
As to weather the crack is the cause of your poor running that is one of those how long is a piece of string questions.
The wear & vertical scratched in the bore will not make the engine run better and that crack will not improve the running either.
It could be allowing excessive oil into the cylinder fouling the spark plug for example .
SO the first thing is to grind out the crack & polish the edges then new rings.
Have a good look at the air induction system as you are getting dust into that engine
Better would be to get the cylinder bored if you can get oversized pistons .
However if that is a cool bore, all aluminium engine then it can not be bored out
he alloy they use is an aluminium silicon copper casting alloy with high iron impurities & usually high chrome , nickle or titanium.
The last 3 come from remelting scrap and cause finner grain size .
The iron causes an iron silliside to to form on the wall of the casting, particularly is the core for the bore was a chill.
The depth of this high iron phase is very shallow but it provides a harder wear surface for the rings to run against.
This is std practice for model aircraft engines and basically the bore is just honed after casting.
Now I have never sectioned the barrel of an all aluminium engine so can not confirm this but I have sections a lot of model aircraft engines and made tons of casting ingots ( sticks like solder actually ) for factories making the castings .
And note Joed , because Australian business is lazy & we are stupid, we send the castings over to Italy to be turned into complete engines thus do the hard work to give a competitor an advantage over the locally made product .
Now getting back to your engine
If it is a cool bore the depth of the iron rich region may not be big enough to allow the engine to be bored out.
Thus the new bore will wear very rapidly in use because the rubbing surface will be too soft .
So if the engine maker does not supply oversized pistons that is why & the engine can not be rebored oversize .
IT IS NOT A SCRATCH.
Scratches go along the bore not around it
It is a corrosion pit
It will be a lot deeper than it looks & feels but most importantly the rings will also have been damaged .
And this is verified by the big difference in the wet & dry compression readings
The piston grooves could also been damaged , they usually are .
As to weather the crack is the cause of your poor running that is one of those how long is a piece of string questions.
The wear & vertical scratched in the bore will not make the engine run better and that crack will not improve the running either.
It could be allowing excessive oil into the cylinder fouling the spark plug for example .
SO the first thing is to grind out the crack & polish the edges then new rings.
Have a good look at the air induction system as you are getting dust into that engine
Better would be to get the cylinder bored if you can get oversized pistons .
However if that is a cool bore, all aluminium engine then it can not be bored out
he alloy they use is an aluminium silicon copper casting alloy with high iron impurities & usually high chrome , nickle or titanium.
The last 3 come from remelting scrap and cause finner grain size .
The iron causes an iron silliside to to form on the wall of the casting, particularly is the core for the bore was a chill.
The depth of this high iron phase is very shallow but it provides a harder wear surface for the rings to run against.
This is std practice for model aircraft engines and basically the bore is just honed after casting.
Now I have never sectioned the barrel of an all aluminium engine so can not confirm this but I have sections a lot of model aircraft engines and made tons of casting ingots ( sticks like solder actually ) for factories making the castings .
And note Joed , because Australian business is lazy & we are stupid, we send the castings over to Italy to be turned into complete engines thus do the hard work to give a competitor an advantage over the locally made product .
Now getting back to your engine
If it is a cool bore the depth of the iron rich region may not be big enough to allow the engine to be bored out.
Thus the new bore will wear very rapidly in use because the rubbing surface will be too soft .
So if the engine maker does not supply oversized pistons that is why & the engine can not be rebored oversize .
