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 'Running in' a Bantam racer

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Number of posts : 156
Registration date : 2011-07-25

PostSubject: 'Running in' a Bantam racer   Wed Apr 25, 2012 6:16 am

Am I correct in thinking that this chap's running in method would not be good for a Bantam?
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Mick Potter


Number of posts : 125
Age : 61
Localisation : Cheltenham
Registration date : 2007-06-09

PostSubject: Re: 'Running in' a Bantam racer   Wed Apr 25, 2012 10:53 am

Hi Jimmie.
A very interesting site, but as usual not giving all the relevant information
I agree with most of what is said but not all.
If an engine is run in to gently it will suffer blow by of combustion gas past the rings, glazing of the bore will result and no amount of thrashing will regain the lost potential.
All engines will lose power over their life spans. If an engine is run in hard it will have a higher initial HP output but will tail off quicker. If an engine is run in less vigorously it will have a slightly lower HP output but will hold on to its maximum for a great deal longer. If graphs of both types of running in are compared, the aria under line will be equal. The choice is there for anyone to make. Either make maximum power and refresh the engine at low mileages or go for slightly less power with reliability.
On his comments on manufactures recommendations for running in, he correct in saying that they are too conservative. I believe that the best way to run in an engine is to start at half max revs and explonantualy increase over time.
What he omitted to comment on was excessive engine speed when running in. He rather gave the impression that it’s impossible to over rev an engine when running in (NOT SO). Contradicting what he said (and this only applies to 4 strokes), giving no regard to running in WILL destroy the oil control ring. In a 2 stoke it WILL result in a seize.
I have no evidence for my comments apart from 35 years working in the trade on hundreds & hundreds possibly into the thousands of different bikes (knowing the customers and how they were ridden).
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Number of posts : 156
Registration date : 2011-07-25

PostSubject: Re: 'Running in' a Bantam racer   Wed Apr 25, 2012 7:22 pm

Hi Mick

Many thanks for your easy to understand reasoning. As with most things in life, thinks are not as straightforward as they seem.

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john bass


Number of posts : 1742
Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: MotoMan...   Wed Apr 25, 2012 10:25 pm

He did start by saying this subject is controversial so he should not be annoyed at the following. By the sound of it MotoMan has never had to tune many Bantam Racing engines. Piston ported bore distortion is probably something he knows little about. Mass Production petrol engines have their pistons profiled according to lengthy development and durabilty test programmes such that a few mintes "Hot Test" (No-Load Break In) has taken the place of lengthy dyno tests which are done at the rate of one in so many thousands -- according to which levle of Sigma QC programme the Auto Company runs.

With the racing Bantam it comes down to either having a loose piston -- more piston-to-bore clearance than necessary -- or taking time to profile (shape) the piston to suit the shape of the bore at MAXIMUM HEAT conditions. Thus Mickīs comment about full-bore running comes into the picture; if the break-in run does not include a good full throttle period the important bit of piston-shaping will be missed and this thing of bore-glazing can occur. On the dyno a quick run up to max load, full speed would give a good definition of where the high spots are to begin the profiling ... and thatīs only the beginning.... On the track its a bit more time consuming but a properly shaped piston is worth it....

We had a handy instrument for looking at cylinder walls by just taking the injector out -- with diesel engines on dyno test, that is. I forget the name. It was something like Infrascope or Intrascope. Hand held, like a normal flashlight it had a long flexible pipe which was inserted into the cylinder via the injector hole. There was a viewing window at the opposite side to the the flexible pipe and a knurled ring for rotating and angling the "Eye" -- the lens -- at the end of the pipe. Battery light on and the viewer could see the clyinder wall all the way round and all the way down the bore with piston at BDC. We used this frequently with our new engines during Break-In...

I was thinking it would be a handy tool for Bantam tuners using a dyno -- well, also for trackside use??? Before whipping off the head -- take a decko down the plug hole.

Bit of a costly LUXURY I suppose?

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