Vega 9cc v twin

[Maryak]

My other concern is bell mouthing. My feeling is that I should proceed with the bottom of the cylinder towards the chuck and not take the top past the cutting area of the lap but just up too it.
Or would that be opposite and actually cause more to be taken at the top? ???
Any thoughts?

Thanks,
Peter.

Pete,

Oddly enough the bulge in the lap created by the wedge actually helps to achieve a parallel bore as in micro terms more metal is removed in the centre where the bulge is. A slight taper of 0.0005" is said to help as long as the smaller size is at the top where the contra piston is located. Personally having built 2 of this type of engine a good finish and mate between piston and bore is most important and a tighter fit than you would think for the contra piston are the keys to success. The final mate of piston and cylinder using tallow is also very well worth doing.

Best Regards
Bob

 

[Mo deller]

Hi Peter.
I had a quick look at my Sparey book - I was sure Mr Sparey mentioned somewhere that you could use slight bell-mouthing to your advantage for IC engines. I don't see it in the section on lapping though, but I _think_ it is referenced somewhere in the book (if you are referring to "The Amateur's Lathe") - but the top of the cylinder must be toward the chuck - in effect making for a slightly tighter dimension of your cylinder, and thus higher compression at TDC in the engine.

Not much, I know, but HTH.

Regards, Arnold

Hi Arnold,
I remember reading somewhere about the top of a cylinder being the chuck end but I thought that was for the initial boring as it tends to be smaller the further up the bore due to the forces acting on the boring tool. Not sure about lapping though. Yes it is the Amateur lathe book I have. I'll read some again.

Thanks
Peter.

 

[Mo deller]

Pete,

Oddly enough the bulge in the lap created by the wedge actually helps to achieve a parallel bore as in micro terms more metal is removed in the centre where the bulge is. A slight taper of 0.0005" is said to help as long as the smaller size is at the top where the contra piston is located. Personally having built 2 of this type of engine a good finish and mate between piston and bore is most important and a tighter fit than you would think for the contra piston are the keys to success. The final mate of piston and cylinder using tallow is also very well worth doing.

Best Regards
Bob

Hi Bob,

No contra piston to worry about,this is a fourstroke glow. Also got piston rings so I don't think I have to lap piston or rings.
I am worrying about getting the technique right so as not to create the bell effect. That is, should you clear the bulge each stroke or keep it within the length of the cylinder.
On the other hand if it is the bottom I cant see a few thou will make a difference and the piston rings will not get near the top so does it really matter?
Thanks for your input.
Peter.

 

[steamer]

Instead of the wedge, you can substitute a set screw that will spread the gap. Put it about mid span of the slot and then when using the lap, keep turning the piece part end for end an the bell mouthing will be minimized....if that is what your after.


Dave

 

[Mo deller]

Instead of the wedge, you can substitute a set screw that will spread the gap. Put it about mid span of the slot and then when using the lap, keep turning the piece part end for end an the bell mouthing will be minimized....if that is what your after.


Dave

That may well be what I'm after Dave. Not understanding what can cause it I am unable to decide the best method.
I think the time is approaching to just get on with it

Thanks
Peter.

 

[Maryak]

I am worrying about getting the technique right so as not to create the bell effect. That is, should you clear the bulge each stroke or keep it within the length of the cylinder.

Peter,

Sorry about the mix up regarding engine type. I would try and keep the bulge within the cylinder most of the time. I suffer from wild imaginings as I stand there bored stupid and lose concentration, hence "most of the time" :

Best Regards
Bob

 

[Mo deller]

Well so far so good.
I used a piece of scrap to experiment with and all seemed to go well. I think it helped to get a feel for the process and to calm my nerves ready for the real thing.
Sorry I havn't got photos yet but I was just in the mood and feeling good about it so carried on with the first cylinder and removed 1 and a 1/2 thou with fine valve lapping paste mixed with a little auto transmition fluid. I had prepared two aluminium bore gauges with 748/749 thou on one and 750/751 on tother. All machining marks are gone and the 749 is a nice fit right through. It was at this point I though about photos but I was just a tad grubby ;D
The wedge stayed put so I guess my wobbly sawcut was perhaps a bit of serendipity.
I will do the other cylinder now before cleaning everything to start with something finer for the last thou. I have solvol autosol and Brasso. Not sure if the solvol is finer than the paste,it feels quite gritty in comparison.

Should I just use Brasso now or solvol first then Brasso or maybe there is something inbetween?

ttfn
Peter.

 

[zeeprogrammer]

Oh yes please pics. This lapping process is of great interest.

Fine looking cylinder!

 

[Mo deller]

Well...... I think I have a pair of useable cylinders. After cleaning all the parts I decided to go with the Brasso. Had a little trouble with things starting to snatch. Ended up with more oil in the brasso,probably 50%. This was better but every now and then I would feel things starting to get lumpy. Not sure why.
I was telling my brother about it this morning and he asked how fast I was running the lathe. It was one of those,why didn't I think of that moments. I was using middle speed I think about 600 on the Myford so slowed it down to 300. This was better again but still every now and then it would tighten.I just took to stopping to wipe it down and refresh things to start again.
For this last lap I did 3/4 hour on one and 1/2 on the other to get them both to take the 750thou gauge.
I have tried to show what they looked like after each process with a close up photo.
First a cylinder before

Now lapping set up using the fine grinding paste

Cylinder after first lap

After last lap.

And finally how it looks to the naked eye

As for trying to get some pinch at the top of the cylinder I found impossible to do with this lap. I just couldn't feel a tight spot while working so didn't know where to stop my movement along the lap. I just kept it moving around the middle.
I think I ended up losing the barrel shape after the first lapping.Must have taken 20 thou off the lap as the grooves started out 40 thou deep (my guess as to what would do as I found no reference about how deep they should be) and were looking about half that.

Maybe that's where a type that expands at the end would prove better.
I guess I'll have to wait and see if the thing runs before I know if I made a good enough job.

Hope you like the piccies zee

Peter.

 

[mu38&Bg#]

Doesn't this engine use piston rings? You don't need taper in that case.

 

[Mo deller]

Doesn't this engine use piston rings? You don't need taper in that case.

Yes it does. I understood that although not essential a very slight pinch at the top would be beneficial.

 

[zeeprogrammer]

Hope you like the piccies zee

I do indeed Peter. Thank you very much. The close-ups were also very helpful.

 

[Maryak]

Nice lapping job. :bow:

Best Regards
Bob

 

[Mo deller]

I have made some piston rings from cast iron and split them all using a vice and pliers with no problems. This was how the designer did them and it worked for me.

Next I tackled the pistons and as I need two I decided to make four just in case.I spent allot of time thinking things through and asking questions here about the gudgeon pin holes. I had intended to drill the holes first but changed my mind when I saw somewhere else some that were being drilled last and thought that looked better. It would have been if I could have done it in the rotary table but I hadn’t checked the height and just could not get enough room.
Plan B then was to make a fixture to bolt them onto my angle plate. Apart from being more work and taking longer to set up this worked well.
After turning and boring the ring groove was cut.

Then onto the mill to cut the slot for the con rod.

I used my dti to set the slot level ready to cross drill. A bit fiddly.

Reamed by hand

That completed the work on the mill.

Back to the lathe then and I made a spider to help hold the pistons and act as a back stop. Something I learned on here. Thanks whoever that was. Cut off the spigot with hacksaw and faced to length.

I now have twice as many pistons as I need.

ttfn
Peter.

 

[richcox88]

hi peter

great work

im 21 and own a ml7 and ive just started making an engine the malcolm stride lynx(ne15s) but stuck now as i have done the lathe work i can do because i now need a mill lol just wondering if you know the magazine numbers the vega is in with plans as i would like to build this at some point.

thanks
Rich

 

[Mo deller]

hi peter

great work

im 21 and own a ml7 and ive just started making an engine the malcolm stride lynx(ne15s) but stuck now as i have done the lathe work i can do because i now need a mill lol just wondering if you know the magazine numbers the vega is in with plans as i would like to build this at some point.

thanks
Rich

Hello Rich, thanks for the compliment. I like the ne15. I bought Malcome Strides book recently after seeing the engine. Shame the plans are no longer available.

The Vega was serialised in 1986 over six issues of volume 156 numbers:-
3768 Jan 3-16
3770 Feb 7-20
3772 Mar 7-20
3774 Apr 4-17
3776 May 2-15
3778 Jun 6-19

Good luck
Peter

 

[ariz]

great work peter on those cylinders, pistons and rings!

you said that there were not problems in splitting the rings in the vice with a plier, but I was been afraid to broke them

 

[bananaman]

Hi Mo

can you (or anyone) give me sme advice on how to set the timing for this engine, I have built one and this is the last thing to do but i have no info on how

thanks

Bananaman

 

[NickG]

Nice work peter. Lapping is something i've never really got to grips with. I tried making a wooden dowel lap with wet & dry paper wrapped around it for my flame licker, it resulted in a good finish but a non round non parallel bore. So I used an adjustable reamer with plenty of oil and that gave me good results and an acceptable finish.

The problem I see with your lap is you have to use it at every point in the bore the same amount, where as the reamer is the same diameter all along. Having said that, it seems to have worked well for you.

Nick

 

[Mo deller]

Hi Mo

can you (or anyone) give me sme advice on how to set the timing for this engine, I have built one and this is the last thing to do but i have no info on how

thanks

Bananaman

Welcome to the forum Bananaman,
I would love to hear and see details of you and your Vega. Perhaps you could post something in the welcome section for us.

I have sent you a pm with the details I think you need.

Peter,