Lapping cylinders, with what?

[PeterE]

Reading about engine making in different places I found one that stated that it would be more or less mandatory to lap a cylinder bore before bringing into use. Sounds like a very good advice, but what to use?

I read in GHT´s workshop manual that it should preferably be carborundum material used for this and not diamond as diamond more easily beds in and remains than carborundum. To me it may be true and equally well could be GHT´s personal opinion, I haven´t got the faintest .... and would very much like some additonal info.

If going for carborundum, would valve grining paste be a useful lapping paste? It seems to come in packs with two grades, fine and coarse. Would that provide a useful surface finish? ... and it is easy to find.

BR

/Peter

[Jasonb]

Valve grinding paste is a bit too coarse. You can buy small amounts of lapping powder down to 600g quite easily and if lucky find 1000g.

Have a look at this thread where I give details of powder suppliers, just mix a small amount with oil.

http://www.modelenginemaker.com/index.php/topic,855.0.html

And here is a bit about using them at the bottom of the page and lapping teh piston to the liner is on the next page

http://www.model-engineer.co.uk/forums/postings.asp?th=70308&p=1

J

[black85vette]

One of the threads that Jasonb links to is one I started.   I got 3 of the grits from Veritas.   What I like about them is that you pay for just the grit not the oil or grease.   On the premixed stuff you get 2oz but most of it is grease.   With the grit only you mix up just what you need and can use heavy gear oil or grease to suit what you are doing.   Plus it worked well.

[Doc]

This is what I use and has done me well on all my engines of coarse the size they offer will last me forever.
I have used the 240 grit on all my engines with very good results.
Clover Silicon Carbide Lapping Pastes

[PeterE]

Thanks a lot for commenting everyone! Much useful info!

I found that the grain of the Holts valve grining paste is probably 180 and 320 from the various sources I managed to dig up. That would mean that the fine one should work quite nicely to lap the bore of my Trojan cylinder.

Unfortunately the cost of getting other lapping powders or pastes from UK/US to Sweden makes them too costly, so I think I'll stick with the fine valve grining paste for now.

Thanks again!

/Peter

[Jasonb]

Does Germany work out any cheaper, bottom of page. Postage upto 1kg would be 11euro

http://www.fine-tools.com/abrichtblock.html

J

[PeterE]

Hi Jason,

Thanks for the link! Put on the useful links list 

The price for the Holts valve grinding paste kit is 12 euros (about 120 SEK) so adding 11 euros will be a lot. I think I will try with the kit for starters and if I am not satisfied I will shop around for something better - I may even find some "must have" tools along the way 

BR

/Peter