5 CC CI engine (and a bit of a Grump)

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5 CC CI engine (and a bit of a Grump)

This topic has 41 replies, 15 voices, and was last updated 30 October 2011 at 20:56 by Sub Mandrel.

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7 October 2011 at 10:44 #75937
David Clark 13
Participant
@davidclark13
Hi There

The reamer is not required.

I have just looked at the drawing going into 4415 and it is a 1/4 reamed hole. Not 7mm as Ramon has stated in the text.

The 7mm is the counterbore that is stated in the text as 7.5mm.

regards david
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7 October 2011 at 12:10 #75941
Ramon Wilson
Participant
@ramonwilson3
Hi Guy’s

Oh dear I really have mislead you here I’m afraid – well sort of.

When I built my two engines and indeed the Etas too I did ream the main shaft 7mm thru with a short 2mm deep 7.5mm counterbore for 6.35 finished shafts. The inner shaft was made to suit and, as stated in the text, the whole lot was turned between centres after Loctiting. When I drew it in Cad I must have overlooked that fact and drew it as shown. I certainly didn’t realiise it conflicted with the text

However I’m certain that providing the inner shaft is made accurately before Loctiting and is a good fit in the main shaft there should be no problem with concentricity.

The easiest way around it, though not an ideal way of going about things, would be to change the design slightly and keep to reaming 6.35 through and reducing the front end to 6mm between centres making sure you remember to ream the collet 6mm and thread the spinner nut M6 too. This will be more than adequate – the Eta Mk 1 has a 6mm (as designed) front end and is running well.

Dick you really should not need to put a seal behind the front bearing to maintain crankcase pressure. The scuffing was probably due to some miniscule bit of debris that allowed the shaft to pick up. I have not experienced the problem before or since – in any engine. It is usual to allow the fuel to reach the front bearing by allowing a degree of leakage down the shaft. Though both Racers have open bearings at the front I have removed the inner seal on some front bearings to prevent ingress of dirt but allow lubrication from the rear. As far as two stroke diesel and glowmotors are concerned I have never seen a seal being used.

The drilling of holes for the transfer ports instead of radial slots should be okay but I would imagine the performance may possibly drop off a bit due to the opening being gradual. That said several designs feature this kind of porting so don’t perceive it as a great deviation. Drilling the holes at an angle towards the top of the bore however will increase the transfer period – just as in the Eta’s

Bill – Thank you for your kind words of reassurance. I do realise that despite trying my damndest mistakes will happen – it’s just not nice when you realise others are relying on you not to make any

This is fast becoming a salutory lesson. It is the first time I have had a design published and can see that far more care will be required should anything materialise in the future. All I can say – promise – is that I will take note and update the drawings as and when required.

Finally Dick could I just say that my name – Ramon – was not of my choosing, that was defintely beyond my control, but it is my name and that’s the way it’s spelt. I have had several nicknames over my years the ubiquitous ‘Tug’ being the usual but I don’t refer to it on here. That said however I’m definitely not a ‘Raymond’ either.

Regards to all – Ramon

Edited By Ramon Wilson on 07/10/2011 12:12:09
7 October 2011 at 14:12 #75945
David Clark 13
Participant
@davidclark13
Hi There

We all make mistakes.

Even Martin Evans was known as Martin Errors.

In 5 years time you will be turning out perfect designs.

regards David
7 October 2011 at 15:43 #75949
Richard Parsons
Participant
@richardparsons61721
Ramon, Sorry I was not looking at the web-site when I wrote my little bit.

Your comment about the use of an oil seal being somewhat unusual is odd to my mind. Since I came over to Hungary I have almost ‘made a corner’ in repairing 2-stroke chain saw and strimmer engines. Hungarians are the world’s greatest wizards at breaking things. All of these have oil seals in them. So I am going to try them here.

I now have about enough information from your postings to refigure the transfer ports. Your suggestion of drilling them at an upward angle seems good but I will only do so in those regions of the cylinder which do not face an exhaust port. Those holes will be at Right Angles to the bore. This will direct the fresh gasses into the centre where of the cylinder the ‘pent headed’ piston directs gasses upward. The idea is to avoid losing too much of the fresh charge and getting rid of the spent gasses.

When I have lapped in the piston I want to hear a descent ‘pop’ when the transfer ports open. This means minimising the dead space in the crank case.

As to nick names I have had many including ‘Chewy’ aka ‘Chewbacca’ I was very large and hairy!

Rgds

Dick
7 October 2011 at 17:29 #75952
Ramon Wilson
Participant
@ramonwilson3
Five years David? that’s a lot of engine building time – I hope it doesn’t take that long to get to a decent stage

Dick – I was refering to small model aircraft engines – well up to 10cc as I’ve no experience with anything larger.

I didn’t realise you were thinking of adding ‘extra’ porting between exhaust areas – it will be interesting hear if your results provide an increase in performance.

I have to stress I have no ‘scientific’ background on these small engines other than having operated them in various forms over many years. It’s only in recent years that the ‘internals’ have been of interest to me but I’m at the bottom of a very long stairway as far as these inner workings are concerned.

Something I have pondered over however is that some engines have – relatively – enormous passages cast or cut in the case to get the fuel up to the actual transfer passages cut through the liner. This leads me to think that as this must increase crankcase volume it must also have an effect on lowering case pressure which is what takes the fuel through. Whilst sufficient fuel obviously needs to transfer surely doing this at a higher pressure, obtained by keeping the case volume to a minimum is a benefit. The actual (case) passages on the Racers though quite wide are relatively narrow just .5mm but appear to give more than sufficient fuel at higher revs.

Anyone with any thoughts on this matter?

Regards – Ramon
23 October 2011 at 19:43 #76727
Ramon Wilson
Participant
@ramonwilson3
Hi ‘Guy’s’

I have just had an email from someone making this engine pointing out another omission this time on the Liner and Piston drawing.

The overall dimension over the exhaust flange is 26.0mm and the outer diameters top and bottom are 22.0 to fit both the case and cylinder barrel (fins). It’s ideal to have the fit in the barrel a nice tight but slide fit for better heat transfer but that in the case can be eased some what. If anyone decides to shrink fit the fins on the liner remember that that will in all probability distort the liner so the lapping would need to be done after such fitting. Given the likely use of this engine though I feel to fit the fins in such a manner is totally unneccessary.

Finally a reminder that simple En1a free cutting steel is perfectly adequate for this component if the engine is not going to be used on a regular ‘working’ basis ie fitted to a model and flown though even then it will last quite some time.

Although this material is mentioned in the text I have not drawn attention to the fact that the last three Eta engines used En1a and the piston liner fits in those are bedding in superbly and it is something I will certainly use again in the future.

Liner and Piston drawing duly updated.

Apologies for the ghosting on the cutter area – can’t understand why that’s happening at the moment but the salient bits are clear enough!

And yes – once again, another ‘Sorry about that’ is due

Regards – Ramon
25 October 2011 at 21:05 #76865
Sub Mandrel
Participant
@submandrel
Ramon,

Your cutters are things of delicate beauty, so I hate to criticise, but for similar tools I don’t bother with side clearance, or if I do just machine the disc from which the cutter is made slightly concave. Instead of your elegant curved backs, i just mill across at an angle to leave the slightest witness behind the cutting edge.

‘Works for me’

Neil

Here’s a nice big endmill making a little three-gang cutter (to an ETW design).

And proof it works:

Edited By Stub Mandrel on 25/10/2011 21:07:39
25 October 2011 at 22:55 #76875
Ramon Wilson
Participant
@ramonwilson3
Hi Neil,

Yes I know where you’re coming from and indeed thats how I set out on these cutters originally. I dished them both sides thinking that that would be sufficient clearance after all it’s only the very tips that are doing the cutting. I think the problem here was mainly due to the thin nature of the cutter and not enough meat to allow a sufficient clearance angle.

However those first two just rubbed and wore so quickly and did in fact spoil the first (steel) cylinder (not referred to in the text!). The last, as said sailed through with ease however the fact that it was left hard – ie not tempered – as well as backed off probably improved matters as well.

As drawn it is, I confess, a bit of artistic licence without realising the implications. This is how they were actually made the bottom right hand one being the one that worked very well – still usable infact

Hmmm, I’ve only just realised that I drew them with three teeth and made them with five

Thanks for your input though – all noted for any future drawings

Regards – Ramon
26 October 2011 at 10:37 #76897
methusala
Participant
@methusala
Hi Ramon,

Hmmm, I’ve only just realised that I drew them with three teeth and made them

with five.

I would have a recount if I were you .
26 October 2011 at 10:58 #76899
Ramon Wilson
Participant
@ramonwilson3
Hmmm, infact double *&^%* Hmmm

Attention to detail that’s my motto – well it used to be, I’m just getting bloody old and I don’t sodding like it

Does any one else have moments like these – they’re getting a bit too frequent for my liking – oh well just keep smiling

Regards – Ramon
26 October 2011 at 11:06 #76900
Clive Hartland
Participant
@clivehartland94829
As said, ‘Keep taking the pills and smile’.

Dont let the detail get you down Ramon, you did good and its published and as always something is found by people, that you took for granted and they make an exception!

Clive
26 October 2011 at 20:55 #76927
methusala
Participant
@methusala
I’m sorry Ramon I didn’t mean to offend you, Please accept my apologies, No you are

not alone, I know that I do the same sort of thing on a regular basis , and I’m sure others do

as well.
26 October 2011 at 21:33 #76931
Steve Withnell
Participant
@stevewithnell34426
I tell you what, this thread has convinced me never to submit anything for publication!
26 October 2011 at 22:24 #76933
Ramon Wilson
Participant
@ramonwilson3
Colin,

Please – absolutely no need to apologise and absolutely no offence taken I assure you – really. Indeed I couldn’t believe what I’d written once you’d pointed it out.

That was exactly my point – It really does surprise me as to just how much slips me by these days – I had a true Classic with ‘Wheeltappers’ Nemmet 15 – Better have a good laugh I’m sure others will be.

Seriously though I do find it becoming more and more impossible to keep even a couple of balls in the air these days – at one time it was several – honestly – but I’m definitely quite adept at dropping them these days. Thanks for your words of suppport though Clive, I am from the school that says ‘must try harder’ though but I’m beginning to feel less and less like beating myself up about it.

Steve – don’t let anything put you off – nobody’s beating my door down and despite what you might think it has been well worth it. I know just how I’m going to feel if just one engine gets built and whoever makes it gets as big a thrill as I did when it runs

I’ve finally got back onto the lathe today – it’s been a fair break – first off is a new, larger saddle handwheel for the Myford and then some work on the Waller engine

Off to bed with a big smile on my face then and looking forward to tomorrow

Regards for now – Ramon

Edited By Ramon Wilson on 26/10/2011 22:29:59
28 October 2011 at 09:05 #76977
Anonymous
Posted by Steve Withnell on 26/10/2011 21:33:43:
I tell you what, this thread has convinced me never to submit anything for publication!

That’s a shame, I’m sure it would be an interesting read.

Regards,

Andrew
28 October 2011 at 10:56 #76980
Ian S C
Participant
@iansc
Never say never! Ian S C
30 October 2011 at 20:56 #77089
Sub Mandrel
Participant
@submandrel
Ramon,

I’d worry when you think you’ve made a twin and it comes out as a V12…

Neil
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