I've read on the boards that some people will polish the piston and sleeve with a light polishing agent before break in to cut down on break in time signifigantly. I had my questions about this and never got a good definitive answer.

I tried breaking in my new SX12 yesterday. 2 hours and maybe a 1/4 tank, since I could not get it to start reliably for anything. So today, I grabbed my rotory tool and some Colgate. About 30 seconds with a rotary tool and a liberal cleaning, WD40ing and after run oil, and the engine starts up with no problem. I just finished heat cycling it for my first full tank.

Anybody else support/oppose this method? I really hope I didn't do irreperable damage to my new, worked engine.

The method is good but just need to use the right tools and polishing compond! Definitly not Colgate and WD40.

I have heard of that method before from an engine guru. Well, my feeling is that as long as the engine runs fine, then you are fine

On some brands of engines ( actualy most of them), to have engine running longer and better it is the best to lap it before initial start. I am always doing, regardless the brand.
Well I am against to use Cogate or other sustitute to real lapping compaund and using rotory tool ( any kind of power tool) is realy dangerouse because it is hard to control fitting condition.
am using old hand lapping method-lapping compaund 1500 grid from Clover ( oil based) and lapping tool for piston. I am sugesting to don't lap sleeve-only the piston.
I can give you my numbers for fitting piston to sleeve after lapping is done- for 12 Novas engines it is 3.1-3.0 mm ( initiay it is 4.3-4.5m) and for 21 engines it is 4.2-4.3 mm ( initial 5.7-5.8).
To mesure this fitting I do following- I clean piston and sleeve with denaturated alchol and fit piston inside sleeve with slight force till it got stock on the top and then mesure the distance from the top of the sleeve to the top of piston.
There is to thing needs to be taking care of-wash everything very good after lapping is done ( if any lapping compaund will stays there it will ruin intire engine within a second) and second thing is try to do everything possible to don't make ellips on piston.
Unfortunatelly I don't have digital camera to put pic of my lapping tool, but I made couple of them for my friends and may be they can put pics of it.
Good luck and be patient.
Edward

I thought the idea was to recreate the up and down motion from a running engine by hand, with a little lapping compound. Therefore laping the piston to the shape of the sleeve and making a perfect seal.

I got a brand new JP on a Friday afternoon. Used some autosol to lap it in. Fired it up on saturday and ran a couple of tanks thru it.

Ran a 10min heat. A bit rich.
Ran a 20min final after that and the motor was just as fast as the guy that TQ in a straight line. Pity about the corners.

So I reckon it works.

Hi Steeve.
Piston and sleeve have their own geometry and you don't want to have tapering on piston the same as on sleeve.
Tapering on sleeve is done to compensate thermoexpention and tapering on piston is done to remove extra friction-so they are totaly diffeent.

Well said Edward, I dont know all those numbers at all but I just know Colgate and WD40 should stay in the bathroom and garage, not the engine!

Point well taken. The reason I used teh toothpaste is I know it is often used as a low abrasive polish for lots of metals, believe it or not. Since I wasn't exactly sure how strong a polish I needed, I figured work with the least abrasive stuff I could think of (and had on hand at the time) The polishing bit I had on the roto tool was about the same diameter as the interior of the sleeve, so the pressure was more or less equal. The WD40 was used only to make sure all the water was removed from the sleeve after I cleaned the Colgate off. In retrospect, I suppose I could have used either the denatured alcohol or the nitro cleaner I had on me.

It didn't dawn on me to use lapping oil on it, which is bad considering I worked in an auto parts store for almost 4 years. Still, since I wasn't sure, I didn't want to use anything too strong and screw the engine up royally. I didn't touch the piston because 1) I wasn't sure it would work, 2) I didn't want to apply any uneven pressure to it and 3) I was just lazy. It's much easier to just pop out the sleeve when the engine is already mounted in the car than break everything down. The engine starts right up, still has a load of compression, and looks to be a monster once I get it broken in (3 tanks so far, 1st 2 minute heat cycle, the next t2 slow rolling in the parking lot, nothing over 1/2 throttle. Even set the endpoint on the radio to make sure)

Thanks ED. Point taken.

EDWARD,
what did you use, to make the lapping tool,,what does the tool look like,,i would like to make one for me.

if any one has a pic. an could post it,i will appreciate it.

A lot of different materials can be use to make lapping tool ( different aplication ) and for this particular I am using "Garolit LE" ( see McMaster car catalog page 3344). I will try to describe it as I can.
It is made out of round bar -50 mm diameter and 25 mm thick.
it has hole on center 13.8 mm and it is like adjustable clamp.
First I cut outside diameter on lathe to 50 mm, then I made a bore 12 mm. Then I cut that to 25 mm long. Next step is I made to three cuts ( under 120 degree) from out side to center. Two of them go only to half way and last one is all the way to 12 mm hole. Next step I made a hole on the place where the complete cut is ( right angle) on one side of of cut I made 6mm hole and other side I threded M6.
Then I put it back on lathe and made bore to 13.8 mm.
Actualy tool is ready to use, but before use it, you need to lap this lapping tool. I use old dead pistons and lap them all the way- so I am making sure internal surface is round and smooth ( always mesure it with micrometer).
I need digital camera, urgent!!!!!!!!!!!!!!

The guy that makes STS engines sez to use toothpaste to lap motors in.

Maybe it aint that bad for them.

Edward, if you need me to take a pic, I can take one for you at CP this saturday.

Can we do it today or tomorow or any other business day this week. Saturday we going out for small vacation. I have in my car second set of lapping tools, so I can stop by in CP any moment.
Please.
Edward