Cylinder Bore 7/8" at a depth of 2.5" OR use DOM/CRS ?

[raynerd]

Hello, I was hoping someone could give me some advice. The next project that I am currently planning requires a cylinder bore of 7/8" to a depth of 2.5". I`m really concerned that to that depth I`m going to end up with a taper as I`m going to have to have my boring bar stuck right out! Infact, I`m fairly sure my boring bar won`t stick out that far! I`m also going to have to buy the cast iron material for the cylinder as it is something I don`t have in stock at that length so it is quite expensive if it goes wrong. Do you think this is do`able - should I give it a go.

The reason I ask is becuase on another project log of the same engine build, someone has used DOM steel tubing (drawn over mandrel), I`d never heard of it but I believe in the UK we normally call it CDS seamless or mechanical tubing. So I`ve found it with an ID of 7/8" but sadly at a very larger length which boosts the price up to £30+ which I can`t justify when I only need 2.5". I believe in the USA a few sites offer to sell it by the inch but I just can`t find anyone that will do that over here. I believe this idea of using DOM for cylinder linings has been mentioned over on HMEM.

So I`m a bit puzzled. Do you think I`m being soft shying away from cutting the bore? I just had the worry to start with and then when I saw someone else had thought the same thing and gone a different route to avoid it, it is now concerning me even more.

Any advice apparecited, either where I can get DOM/CRS seamless by the inch from the UK or how to cut such a long bore?!

Cheers
Chris

[sbwhart]

Chris

Is the bore blind or straight through.

The best way to deal with it would be to drill out as much as you can, then bore, but first make ureself a boring bar make it as thick as you can and just long enough to clear the job, at that size you can make the bar from mild steel with a little bit of HSS held in place with a grub screw, a broken centre drill would be ideal, when you come to the finish cut run the same cut through three or four times to get rid of the spring in the bar.

Boring bar second from left is one I made.



Hope this helps

Stew

[raynerd]

Thank you Stew, that was excellent. It is a through bore for a cylinder for a Webster IC engine. I would prefer to try and bore it so I`m glad you recommend that. As you suggested, I have both some broken center drills and also some little bits of HSS that I`ve accumulated in my box so I`ll make my own boring bar as you have shown. Really appreciate the advice.
Chris

[sbwhart]

Chris

I've not made an IC engine but I understand that you need to hone the bore to get a very good finish, but if you're following a set of plans and build log it should tell you this.

Stew

[jim]

i usually get seamless tube off ebay, i've need some odd ball sizes, always managed to find it!

[raynerd]

Hi Jim

Yes, there is some on ebay :
http://shop.ebay.co.uk/i.html?_nkw=seamless+tube+7%2F8&_sacat=0&_odkw=seamless+tube&_osacat=0&_trksid=p3286.c0.m270.l1313
but it is all expensive when I only need a small length. Or at least I consider it expensive, it`ll cost me the same sort of price for enough cast iron bar to make 3 cylinders...i.e get some spare.

Hummm, I just don`t know. I think I`m still going to stick with trying to cut this long bore myself.

Stew -> the fact that it also has to be a good finish is another thing that scares me, I know Brian Rupnow on HMEM said he used a hone on his cylinder. The plans call for a cast iron or leaded steel cylinder with an alloy piston. Brian and others have also used a Viton o-ring so my plan is to do the same!

Chris

[raynerd]

Do you think something like this would be OK for honing the cylinder?

http://cgi.ebay.co.uk/New-Draper-BRAKE-CYLINDER-HONE-25-57mm-HONING-TOOL-/320635354194?pt=UK_Hand_Tools_Equipment&hash=item4aa75b3c52

[sbwhart]

Yes thats the sort of thing, but you can make your own from ally bar, turn the bar just undersize tap the end a sutiable size split it down the middle then put a screw down the end with a tapered head so that it springs it open then use this with fine grinding paste to hone the bore I'm sure you'll find something on this if you do a search.

Stew

[Bogstandard]

You will find that some people over on HMEM know very little, you have already named one, it is more like the blind leading the blind.

If you are going to be using metal piston rings, then you hone the bore. This gives microscopic scratches to the surface of the bore (and also helps to straighten the bore out whilst doing it) which retains oil on the bore surface while the engine is 'bedding' in. After a while, the rings and bore will wear themselves smooth and the scratches will disappear.

For use with o-rings, the bore must be lapped as smooth as possible, because if you hone, the scratches will rip the face of an o-ring to bits, and it will wear away in no time at all.

[Jasonb]

Take a look at my IHC build over on HMEM, I've recently added the cylinder liner. Hope you are not including me there bogs

The liner is 1" bore and 3 1/8" long, you can see that I use a boring bar made from a bit of 3/4" bar, cross drilled for a HSS toolbit and also how I held the bar in my toolpost. I bored it a little under size and then used one of the sprung hones like your link, run it with parafin as this stops the stone clogging, i'm using CI rings.

BTW you will need the two stone hone as the 3 stone is too big for a 7/8 bore if you decide on a honed finish

Jason

[Bogstandard]

Of course not Jason, I know you are OK.

But you must know the sort of people who I am on about. Stealing other peoples plans and ideas, modifying them so that they then won't work, and then calling them their own.

[John Stevenson]

Can't be me, mine don't work before modification.

John S.

[raynerd]

Thanks for replying. I have to admit I do not know the benfits of piston rings in cast or o-rings so I was choosing o-rings as others seem to have used them on the Webster. I wouldn`t know where to start on cast piston rings having never used them (the 10V I have build just runs off a tight fitting piston with some graphited yarn). If my cylinder bore is 7/8", would the piston rings be cut from 7/8" stock as Jason has showed in his pictures and then just split. Likewise, is the groove that they lie in on the piston just a fraction shallower than the depth of the ring so that it pertrudes slightly - otherwise I guess there would be no point in the piston rings)   I have to admit, piston rings are always something that have confused me despite seemingly being fundemental to most engines!!! I can`t quite understand what they offer over a good fitting piston directly in the cylinder!! Clearly I`m missing something.

Thanks for your replies. With regards to cutting the bore in my original question you have convinced me that I can "try" and do this myself! I guess I need to decide what rings I am using so I can lap or hone the bore.   

[Jasonb]

There is quite a bit to making rings but its not too hard.

Basically the ring is turned to an OD that is the same as the bore, split(not cut) you then spring it open, there are formula for the amount and heat the ring up so it takes on teh shape with this opening. You then put it back in teh bore and adjust until you have a small gap between the ends, in the case of my IHC it was 0.003". The base of the groove is a little less than the ID of the ring.

The piston, alloy in my case is 0.005" less than the liner bore which allows for it to expand.

The reason for rings is there is far less contact area than if the piston was a similar fit to teh bore, therefore less friction and you can use alloy pistons so less moving weight and also being sprung the ring will take up any slight wear.

If you can get hold of the early issues of Strictly IC there is a 3 part series on making rings.

Out of interest what type of ring is specified on the original webster design? I wonder weather some people take the O ring option as being a bit squidgy they allow for not being spot on with bore and piston.

Jason

[raynerd]

Jason, the plans just say the following:

PISTON RINGS - 3/32" X .875"
SOURCE: OTTO GAS ENGINE WORKS
(410)-398-7340
2167 Blue Ball Rd
Elkton MD 21921-3330
http://www.dol.net/~dave.reed/otto.html

1/16" wide rings would offer less friction and probably seal just as well -
simply adjust the ring grooves to accomodate

However on his website, under "cons" for the engine, he writes:

"Possibly needs thinner piston rings to reduce drag and friction (1/16" -vs- 3/32")."

Now I know for sure I`ve seen at least 5 or 6 on the web with O-rings and on the Webster website there are a few completed builds mentioned with O-rings.

OK, I better get reading up on making piston rings as this seems the better way to go!

Chris

[Bogstandard]

I think you would be much better off at this time using Viton rubber o-rings. They are a much easier solution for the Webster, rather than trying to learn all the pro's and con's of metal piston rings.

Get yourself a working Webster first, then on say your next build, try for a metal ringed option on another type of engine. Getting it wrong first time around could easily lead to a non runner.

[sbwhart]

Some great information their John when to Hone and when to lap and what rings to use with each method.

Chris I'd go for the the viton ring method for a first build, I looked into cast iron rings I think its one of those things where you have to have the right techniques along with a big helping of nack.

Stew

[raynerd]

OK, thanks a lot, John, Jason, Stew. I`m glad you have suggested that - making CI rings does look a bit tricky for me! 

http://www.btinternet.com/~sylvestris/rings/rings.htm

....and John, thanks for posting your advice -  , I appreciate it.  I`ll let you know how I get on! I hope you think the Webster is a decent choice for my first IC build. It looks simpler than most.

[Bogstandard]

The Webster is a very good first engine, easy to make and not much to go wrong. Plus running engine builds have been well documented.

Another one to consider is Jan Ridders two stroke that uses a vapour carb. A much larger engine altogether.

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_tweetakt_motor/tweetakt_frameset.htm

John Somers is currently building one, but had trouble getting it started, but when I last talked to him, he said he had mistakenly drilled a transfer hole too small, so he might have got it running by now.

http://start-model-engineering.co.uk/category/jan-ridders-simple-two-stroke/

You start at the bottom of the page and work your way up.

[Dean W]

Hi Chris;
I think you've got good advice here, especially with Bogs' comments, (yes, all of them ; ).
I can offer my two bits, just for something else to think about.  Since the bore for your cylinder goes all the way through, you can
align bore it and have a very good chance of getting a true bore.  The setup looks something like this:



A bar held between centers, which has a cutter held in a small hole somewhere near the middle of the bar.



Your work piece is first drilled undersized through the center, then mounted to the cross slide on the lathe, shimmed up as needed.
Just another way of skinning the cat.

I have to admit, piston rings are always something that have confused me despite seemingly being fundemental to most engines!!! I can`t quite understand what they offer over a good fitting piston directly in the cylinder!!

The piston rings do something the piston cannot do.  They can run against the wall of the cylinder bore with no clearance tolerance.
The piston has to be smaller than the bore, of course, or it simply would not be able to enter it.  Rings, being flexible, can run against
the bore doing the gas sealing chores for good compression in your engine.  
They do other things, but being able to run right against the bore makes them a pretty handy thing.

Good luck with your build!

Dean

[raynerd]

Thank you for the comment Dean. Am I correct in presuming for this method to work, you must ensure that the bar holding the cutter must be dead centre in the hole/bore you have cut ready? And also that this method will just take the final cut to size as there is no adjustment on the cutter? Seems a smart little method - I think I`d be worried about centering the bar in the original bore from the start.

Totally  , I was browsing your site Dean, back in October and saw the Jerry Howell - Propane burner that you have build. I ordered the plans and they arrived yesterday.  another one to go on the growing list, along with the long list of things I`ve build that haven`t run. Sad thing is, I now realise why some aren`t running but I just can`t find time to try and fix them! So anyway, just wanted to say thanks for an excellent writeup and build of the burner!!

Chris

[Jasonb]

You can adjust the cutter length with sone careful use of a micromiter and a bit of calculation. and yes concentricity is important, you could machine something like the pic and use that as a clamp to hold your liner, so long as you don't remove it from teh lathe it will hold the liner spot on.

J

[Rob.Wilson]

Hi Chris

If you decide to go for a boring bar  between centres ,,, it would be well worth making one of these for setting the cutter 



Great little tool ,, only take an hour or so to make , Design came from one of the early MEW mags   ,,, i could look it out if you want 


Rob

[raynerd]

That is bloody genious! I like that a lot. Considering both yourself and Dean have mentioned this method of boring between centres, is this a method I should look into more rather than the standard boring bar that I was intending on using? Would this give me a more accurate bore with a better finish. My concern with this method is still how to ensure that the bar is setup dead centre of the roughed bore/hole in the work piece. Also I would have to think about how I can hold the job on the saddle and adjusting it so that it is centre. I`ll have to try and read into this method a bit more.

I`m collecting my materials (cast iron) tomorrow so I`m eager to cut, but for once I`ll hold back until I`m clear which method to use.

[John Stevenson]

My concern with this method is still how to ensure that the bar is setup dead centre of the roughed bore/hole in the work piece. Also I would have to think about how I can hold the job on the saddle and adjusting it so that it is centre. I`ll have to try and read into this method a bit more.

Turn two tapered bushes that are parallel in the bore and a good fit on the bar. the OD has to be larger than your bore at one end and less than the pilot hole at the other .
Fit these onto the bar, one at one end small diameter facing inwards, then the cylinder / part then the second bush opposite to the first.
push the bushes tight into the cylinder then pack and clamp up in this position.
lastly slide the bushes out the way and either remove the bar and bushes or just tape the bushes to the bar so they can't foul, then fit the boring tool.

Simples.