K&B 7.5 PRO

[Tunnel-Rocks]

K&B 7.5 PRO

Hi Guys!

Recently I won on ebay a really brand new K&B 7.5 PRO and Im think there is something wrong with this engine, I can turn the flywheel with the hand but its comes tightened, I open the engine and oil the piston and sleeve with WD-40 and add grease to the bearings, it loose something but still tightened, any sugestion?

Thanks and

Happy New Year!

 

[topfuel443]

Re:K&B 7.5 PRO

Most new engines now days have very tight piston and liner clearance at the top. If this engine is new, trust me its normal. once you break it in it'll loosen up some but it should always get tight at the top........or if you are still convinced there is something wrong with id be glad to buy it off of you for a broken engine price : ;D ;D

~ James

 

[Propjockey]

Re:K&B 7.5 PRO

TR--the reason the piston is tight at top is that the sleeve is tapered. The idea is the liner gets hotter at the top, expands slightly more and at operating temps the sleeve walls become parallel.

Hmmm.....doesn't water cooling at the top only defeat this? ???

 

[Tunnel-Rocks]

Re:K&B 7.5 PRO

Sorry TopFuel but this one is not for sale but you guys are right this baby is justs asking for a nice brake in.. ;D

 

[[email protected]]

Re:K&B 7.5 PRO

Tight fit, wow that's good. Maybe you should lap the piston before starting it.

 

[rippinwater]

Re:K&B 7.5 PRO

Lapping the piston is a great idea! The Pro is the tightest piston and sleeve fit I have ever seen. When I first got mine, it was almost impossible to turn over. So I lapped it. Other than the crank breaking in year two, (pros had week cranks) I havent had any mechanical failures. Lapping the piston and sleeve takes a ton of stress off of all other engine parts during break in.

 

[Tunnel-Rocks]

Re:K&B 7.5 PRO

What you mean with "lap the piston" ???

 

[lohring]

Re:K&B 7.5 PRO

I would recommend running the engine rich for a few tanks rather than lapping the piston. The Pro needs to run richer than the earlier small carb engine, and the combination of a tight sleeve and too little oil to the rod will cause failure. Afier this, run it at a normal race setting for a few more tanks, and you should have a good running engine. Lapping the piston can ruin it if you don't know what you are doing..

Lohring Miller