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-   -   K&B 7.5 Inboard help (https://www.rcuniverse.com/forum/speed-rc-nitro-boats-117/885587-k-b-7-5-inboard-help.html)

toonces 06-22-2003 01:23 AM

K&B 7.5 Inboard help
:confused: I have a 7.5 inboard that is older but has a vary tight top dead center too the point that it is impossible to turn over with starter and makes a clicking sound when worked threw that spot ( when the piston goes to top dead center) Piston , sleeve seam to be binding , How do I remedy this so It will start? I think the motor has not bin run much. has bin sitting for a number of years but there is no corrosion that is noticeable.
Any body have experience with this?


Bruce Rolfe 06-26-2003 02:36 AM

K&B 7.5
Back in the mid 90s K&B built some really crappy engines. I owned a 7.5 inboard that blew up everytime I started it. I sent it back to them 3 times. And each time they fixed it, it broke. On Breakin Fuel.
One thing I did on my 7.5 outboard was to take out the glow plug and accach a small chunk of flex cable to the collett and the other end to a drill and turn it over. I lubed mine with Marvel Mystery Oil, Prather After Run oil stuff like that. New motors are very tight on the TDC so break it in carefully. Hope this helps you.

drydock 07-07-2003 04:33 AM

K&B 7.5 Inboard help
With 3.5cc O/B w/same problem I used to loosen the glow plug a bit to relieve compression then fire it up and tighten the plug. Only had to do this 4 to 6X till the eng was broken in enough...
Actually tight TDC is a good sign w/K&B's... Could mean L/N.

Yo, Toonces - Have a hull in mind for the Jet Drive?

Ron Olson 07-18-2003 10:15 PM

K&B 7.5 Inboard help
You might have to loosen the glow plug in order to fire it. Tighten it up as soon as it's fired.
Bruce, K&B had some machining problems before they sold the operation. The crank and sleeve were not square to each other. I know of several people that had that problem. K&B was trying to get out of their warranty by telling owners that it must have been an unbalanced prop or some other lame excuse that caused the engine to go South.
Another break-in trick is to use toothpaste and light oil on the piston and sleeve to hone it.
The K&B's have a tapered sleeve that tightens the piston up at the top end, this is why it is tight there.

nitropower 07-23-2003 12:23 AM

k b 7.5
Is your engine drum rotor or disc rotor? If its a drum and you have disassembled it recently check to make sure the front housing is installed correctly. My 7.5 has billet alum. front housing, which has a flat machined on inside portion. That HAS to be installed up towards bottom of piston,otherwise piston hits frt. housing. Hope this might help.

If its too slow you need more nitro!!!

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