Lapping the Piston/Sleeve
 

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.

Re: Lapping the Piston/Sleeve
 

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

Re: Lapping the Piston/Sleeve
 

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:)

Re: Lapping the Piston/Sleeve
 

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. :lol:

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.

Re: Re: Lapping the Piston/Sleeve
 

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! :lol: :lol:

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!!!!!!!!!!!!!!:cry:

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

Yes!!!
That would be great.....:nod:

Ok, how about Wednesday? Let me know what time.

totaly perfect. How about 12PM? Is this time will be OK?
I also will have with me 21 size set so you can make pics too
Edward

Here is the lapping tool used by TopGun777 for .12 size piston.
http://www2.freepichosting.com/Images/421508365/0.jpg
http://www2.freepichosting.com/Images/421508365/1.jpg


For .15 size
http://www2.freepichosting.com/Images/421508365/2.jpg

Here is the lapping compound used.
http://www2.freepichosting.com/Images/421508365/6.jpg

Lapping tools
 

Thank you very much Marvin. I think it will be very helpfull for all guys who wants to put hands on engines.
Edward

No problem!

Just want to add little bit -it is for piston not for sleeve. For sleeve is different and it is more complecated. ;) :nod:

Thanks for catching that. Edited.:nod:

Thanks for the pics guys!!!!!!
where can i get one of those :confused:

I thought that was a little big to go inside the sleeve

You can ask any machine shop and they will do it for you.:nod:

hey guys check this out, you could look at using this for honging liners, its used for honing out brake cylinders which is a similar size bore as a nitro engine:

http://www.mytoolstore.com/kd/kdbrak08.html

opps i forgot the pic

You can buy honning tool in any automotive store ( $12), but be carefull, I will not sugest to hone ready sleeve and what for you want to lap sleeve? Don't mess with that sleeve ( my suggestion.

Er? Lap the piston, leave the sleeve? Why do you say?

Its too easy to damage the lining in the sleeve. Therefore it is best to just work on the piston and leave sleeve alone.

The sleeve has a chrome coating & by honing or lapping you are removing it. A hone for automotive purposes is to remove the glaze from a bore, be it engine block, wheel cylinder etc. On a nitro engine the glaze (chrome) is our friend. The dude who lapped the sleeve with toothpaste, good luck with your engine but I think you may have decreased the life of it. If it runs hard now & you are happy with it I guess thats all that matters.;)

Usualy sleeve has 3 tappers and it is realy art to make them and it is life important to have them. If you will try to relap sleeve ad you will change tapering-it will end of performance and reliability.
Piston has only one taper ( on the very top of piston, it is vary from manufacturer to manufacurer, and it is not that critical). In general piston id cilindrical, so it is pretty easy to work with that.
It is just my sugestion, based on ... years of expirience. After that it is up to you.
To lap piston for expirinced guy takes about 15-30 minuts. to relap sleeve for the same guy takes 2-3 hours and required much more presision tool and mesuring instrument.
Just try to belive on my words, do not mess with sleeve, even used sleeve with new piston much better then if you will try to relap it.

We can relap sleeve and polish it again, that is not a point, point is-tapering ( please see post above).:nod:

Very good point about the taper, I meant in my reply that honing will remove the chrome & all the polish in the world will not bring the sleeve to its correct ID. I am sure someone with the correct tools & knowledge could do it, but to a person who is not fully dialed in engine manufacture should proably steer clear of anything to do with inside the liner. I modify liners, cranks etc but I wouldnt touch the inside of the liner as I dont have the correct tools or knowledge. also TG777 I have learnt a lot from reading your posts over the past 8 months or so, Keep it up:D

I am realy happy. that myposts help you and many other hobby addicted people to understand something and I will share what ever i know and collected for years in hobby. there will be some points which I will never open ( for instance-how to put bushings inside the conrod and make sure they will never come out, how to cast the cillinder, how much Si in crancase alloy etc,) But general procedure, numbers etc-I am realy open to share.:nod:

I would love to know your secret regards the bushing in the rod, or even better how to make it run on a bearing. I have kept up with the progress on your engines & am looking forward to seeing them on track in Australia. I will probably try one once the Carb is fully sorted.

No bushing secret:D
About the bearing, yes it is possible, but for 21 size, for 12, so far we didn't find solutions for some issues, but we working on it.
You will see pretty soon couple of them there.
Carb is one of the thing which we are working now and progress is going no the way we want to, but eventualy we will be there.
Why you need secret for bushings on conrods-any way I hardly belive you will make them, but if I will release it, a lot of people will make their conrods much better then they are and this I don't want to for them-they have to work hard to find their way.;) :D
It is production seret-it has nothing to do with performance 9 onl the life of conrod)

To prevent the copper bushing coming out on the conrod, you can plated the material rather than forcing 2 object together.

Regarding to the cylinder question. Here are some of my own opinion ( I am not a engine manufacturer and is not in the machinary industry. I just have an genuine interest in model engine production.)

Even the best CNC machine we have today, the manufacturing tolerance is about +/- 0.02mm, unless you start doing machining under control temp, atm etc. But the production cost willl be very very expensive. being massly produced engien, at novarossi etc I don't think every piston and sleeve is made to spec. Pick up a caliper or if you have a height guage and meaure the port on the sleeve. it is at different height from sleeve to sleeve. Some of the line aren't even cut straight. The inside of sleeve and piston is not in perfect roundness (+/- 0.0015). In fact it is not very round at all ( some of you will argue it is made to be elliptical on purpose, but trust me at the cost these engines are exported out of italy, they are not made to be elliptical on purpose).

Personally I think lapping or grinding on the sleeve is better than working on sleeve. because when the engine heats up, the piston usually expands more (that;s why it seizes), working on cylinder making sure it is round will enable the piston to "grow" into something good ( the secret in all modified engien is piston and sleeve fit, not the extra cut on the transfer port). If you work on the piston and make sure it is round but the cylinder is not...... more friction and leakage may result.

Yes cylinder taper is very important. But honing cannot reproduce the tapering. Honing simply removes the coating on the inside of the cylinder ( but the honing stone follows the basic geometry from the brass liner, in other words, if the cylinder is not round, it will not be round). Honing produces the crossweb surface finishing you see on novarossi, rb, jp engine. So see, they are massly produced, not that accurate as you guys have thought.

Grinding can correct any defect in the linder, make sure it is perfectly round and also maintains the taper. But is would be best to grind both piston and sleeve so both are in perfect roundness.

Correct me if i am wrong, any suggestions.....