K&B 7.5 mods

Intlwaters

Help Support Intlwaters:

Mark Anderson

Well-Known Member
Joined
Nov 22, 2002
Messages
827
Raise the exhaust to 180 degrees. Close the rotor at 65. Set the head at .012. Feed it 60% nitro. The old small flywheel helps the handling of most boats. Looks like it is on a tunnel boat. Get a back cut 1450 with around 3.2 inches of cup. The engine will have to be deeper than with an X series prop, but will be much faster.
 

Rod Fonda

Well-Known Member
Joined
Apr 30, 2021
Messages
134
Pretty much what Mark mentioned,looks like the old style engine,hopefully,the piston/liner fit is good,also,you can carefully open up the transfer passages towards the rear boost port dividers with a dremel,,some crankcases I bought later on,came from the factory with the dividers already machined,,You can see if it's been machined or not
 

Alan Elzer

Well-Known Member
Supporting Member
Joined
May 21, 2006
Messages
1,455
Agreed with Mark he's dead on. An Irwin pipe is best one (new style-bigger volume) for me, unless you spend the bucks for carbon pipe from Jeremy from Australia (can give you his contact if needed).
I might have a 1450 that mark talking about if interested.
If your not comfortable doing your own mods, I can help you with that for $75 shipped back (if in USA).
 

Rodney Rogers

Well-Known Member
Joined
Jan 9, 2023
Messages
69
Agreed with Mark he's dead on. An Irwin pipe is best one (new style-bigger volume) for me, unless you spend the bucks for carbon pipe from Jeremy from Australia (can give you his contact if needed).
I might have a 1450 that mark talking about if interested.
If your not comfortable doing your own mods, I can help you with that for $75 shipped back (if in USA).
how much for the prop ? my engine is old may not worth doing mods .
 
Last edited:

Rod Fonda

Well-Known Member
Joined
Apr 30, 2021
Messages
134
Yeah Rod,,if the engine is old,,depends on how much wear it has,, the piston should pinch in the liner at top dead centre with glow plug removed If the bearings are old,you'll need to replace them,might have traces of corrosion,how sloppy is the conrod to crankpin fit ?,,then you have the front bearing/housing/crankshaft seal between bearings that could wear if it's been run with worn bearings,,problem with these engines is that new piston and liners are hard to find,and maybe the large bearing,,some folks in here might have some as spares,,,or just replace the bearings and run it ,might have to run smaller props though, if it's a bit worn out
 

Greg Rowe

Well-Known Member
Joined
Feb 19, 2013
Messages
660
Rodney, PM me if you run into hard to find parts,, bearing housings, piston and liners,
PTO parts, cranks etc.. I bought a large supply of K&B parts a month ago and may be able to help you out.
You have a 7.5 pto shaft with 5mm hex,not square?
 

Alan Elzer

Well-Known Member
Supporting Member
Joined
May 21, 2006
Messages
1,455
how much for the prop ? my engine is old may not worth doing mods .
Just got wife home from surgery stay.. I'll need to see what I have on the prop, but ($20 shipped if I do). If your just playing and not racing just run as is. The older 45's has a smaller crank ID than newer ones, so I'd agree with others not worth changing. (BUT I have new bearings to fit it either way). I'll let you know by tomorrow on the prop.
 

Greg Rowe

Well-Known Member
Joined
Feb 19, 2013
Messages
660
Greg,
I won't be home until Friday....I will look and see if I have one.. your talking about where the drive cable slips in ?? Don't recall ever seeing one made like that,, but I will look.
Do you have a picture of one by chance ?
No pic right now but could maybe get one but yes where your drive slides into the engine
 

Latest posts

Top