tcs719
Active Member
How offton is a rebuild necessary on a 7000 rpm motor? ( hrs )?:help
whats the real scoop?????
- Thread starter tcs719
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fnshrmaster
Active Member
What motor do you plan to run 7000 rpm?
tcs719
Active Member
I have a 98 pm....
whipper
Well-Known Member
Mines at 7500 since 2006 run 7 to 7300 alot. Hours, have no idea but allot. Motor was rebuilt in 2005 ran a year before uping limitter. My motors a 96 225PM. Im planning a rebuild while its still running strong this winter. Best to do it before theres a problem. leak down or a simple compression test will tell ya about health. I would think if your 120 or less its time to tighten up the cylinders with new pistons and rings to get the comp up to 125-135.
The general rule of thumb is dont go over 140 psi and you can still just run pump gas. 140 and up youll need higher octain. Some run pump gas with aces if at 140-145 with no issues. Getting the comp to 130-140 youll have a very strong motor.
The general rule of thumb is dont go over 140 psi and you can still just run pump gas. 140 and up youll need higher octain. Some run pump gas with aces if at 140-145 with no issues. Getting the comp to 130-140 youll have a very strong motor.
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I'm around 148 on pump gas, no problems here.
tcs719
Active Member
Is there a good # to go by?
whipper
Well-Known Member
Do you guys run aces with 91 at all? Or just 93 straight up over 140psi? I was always told by many a builder that you cant run 91 straight over 140psi with very good results? Most gas stations up hear dont have 93oct. Some due like Chevron. On the lakes theres ussually only 91 maybe 92 if your lucky. Ive heard you can run 91octane up to 140 and anything over that 91 with aces up to a point,or if you can get 92 or 93 + even better. I run 91 and for a couple years aces with it. As mentioned zero issues. No point in using 93 or 94 if you dont need to. 140-150 psi you will need to run like those guys mentioned over 91 if available. I would run 91 and aces up to 145psi with confedence.
Ran 91 from several stations in the past, it's still alive.
Jessie
Active Member
What is the compression on each cylinder? What is the leakdown on each cylinder? If leakdown is more than 8%, I would be thinking about a re-build.
njj502
Active Member
There is the best answer, whats your leakdown? Also, if you have about 10-15psi difference between any of the holes you got problems.
I run 91 non-ethanol, twist it all of 7200+ and no problems. Keep in mind guys, you can burn one up in a heart beat runnin 93 octane on 120psi if you get a big slug of ethanol!
suicidealli
Well-Known Member
The question can't be answered!!!!! IMHO. There are a lot of things that have to be entered in to the formula to get the most correct answer. Motor, internal parts, compression, mods, fuel, type of oil, ratio of oil, hull weight, rpms, prop, etc.
It is an average guess. Leak down test I think are the best way to determine health.
If your compression falls off 5-10 lbs it is ready, 10 % leak down it is ready. I don't wait that long.
On a added note the longer you wait past the time of a needed rebuild, cause more damage.
As a new or rebuilt engine wears things start getting a little loose. Usually notice a slight increase in rpms, and mph.
A little less friction on moving parts. "BROKE IN" After that things slowly start going down hill.
When it is ready for a rebuild, and you keep running them you create more wear on pistons, and bores.
Pistons are designed to go up and down. When rings are wore the pistons begin to rock back and fourth a little more.
When you rings are wore, they get sharp edges. The sharp edge will actually start cutting when the piston rocks at the top of the stroke. Also on the other end of the piston the "skirt" rubs the cylinder wall harder. More wear on the pistons.
The very top of the piston also Rubbs and gets sharp when things are really wore. Makes for out of round pistons, and bores. If you decide to wait just plan on boring, and new pistons, or renic. Comes down to a choice rebuild sooner, and try to save pistons, and bores, or wait, and replace everything. JMO
Roy
It is an average guess. Leak down test I think are the best way to determine health.
If your compression falls off 5-10 lbs it is ready, 10 % leak down it is ready. I don't wait that long.
On a added note the longer you wait past the time of a needed rebuild, cause more damage.
As a new or rebuilt engine wears things start getting a little loose. Usually notice a slight increase in rpms, and mph.
A little less friction on moving parts. "BROKE IN" After that things slowly start going down hill.
When it is ready for a rebuild, and you keep running them you create more wear on pistons, and bores.
Pistons are designed to go up and down. When rings are wore the pistons begin to rock back and fourth a little more.
When you rings are wore, they get sharp edges. The sharp edge will actually start cutting when the piston rocks at the top of the stroke. Also on the other end of the piston the "skirt" rubs the cylinder wall harder. More wear on the pistons.
The very top of the piston also Rubbs and gets sharp when things are really wore. Makes for out of round pistons, and bores. If you decide to wait just plan on boring, and new pistons, or renic. Comes down to a choice rebuild sooner, and try to save pistons, and bores, or wait, and replace everything. JMO
Roy
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whipper
Well-Known Member
Haha, Roy you said what Gary Finch once said. {Notice a slight increase in rpm and MPH just before} Gary said, Your motor runs best just before it blows up.:big grin
That little saying has played with my mind on more than one occasion after a great run.:big grin
Its also like an old lady I over heard say to one guy at Christmas years ago. Se said. I hope you get everything you deserve.:big grin
As you mentioned there are many variables. Personally I never thought I would get another season out of mine. The feeling of going out each day hoping it would stay together was unsettling. Much better to rebuild and way less expensive rebuilding before theres any damage.
That little saying has played with my mind on more than one occasion after a great run.:big grin
Its also like an old lady I over heard say to one guy at Christmas years ago. Se said. I hope you get everything you deserve.:big grin
As you mentioned there are many variables. Personally I never thought I would get another season out of mine. The feeling of going out each day hoping it would stay together was unsettling. Much better to rebuild and way less expensive rebuilding before theres any damage.
tcs719
Active Member
Thank you all for schooling me on my motor. Any education i can get. Ill take...thanks