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MG Midget and Sprite Technical - Conrod weight

So conrod weight.
How close do the rods have to be?
They are about 1 gram out total weight but big ends differ about 2 gram.
Onno Könemann

On my engines I balance the rods end to end and overall to within 0.1g.

What are you trying to achieve?
Deborah Evans

The smoothest engine posible
Onno Könemann

Onno, maybe better to leave this balancing to the specialist. Balancing including pistons with a kitchen scale is quite difficult. BTDT.
Alex G Matla

Always a big debate Onno, I would have thought combined rod/piston weight...don't forget to weigh the bearings too.... should be within a percentage of overall weight rather than a specific.I suppose one must look at how imbalanced the system needs to be for someone to notice it. We have found older pinchbolt rod setups on stuff like Bs up to 60 grams different and the engines were as smooth as anything. Out of balance tends to cause a vibration(buzz) at higher rpms, not easily detectable by seat of the pants, worn bearings in a box cause more vibrations! I am impressed you can measure repeatedly to within 0.1 grams Deborah, digital scales to weigh up to 1kg do not seem to be accurate enough for that do you use a calibrated beam scale like we used to have in Chemistry and Physics labs, the enclosed ones to keep air movement away from the measuring because of sensitivity? I use posh American digital scales for my archery arrow making they only weigh up to 200 g and I tend to use grains (just over 15 grains to 1 gram) the machine varies plus or minus 2 grains and I have to keep recalibrating it....blowing gently on the pan can flicker the scales!.....archers like the arrows to be within +/- 5 grains....these are the sort of scales used by people loading their own ammunition....hence the grain scale inclusion.

Peter
P Burgess

When I had my engine balanced by Burton Egineering many years ago, they put in new pistons, and balanced crank and rods, flywheel and clutch. My gear box at the time was relatively new and the engine felt silky smooth. As the 'box got worn and I changed the clutch it became less well balanced. I have since rebuilt the engine, but the pistons, rods and flywheel are the same,( new rings and bearings). The clutch drivenplate was changed when I fitted a type 9 gear box and now the engine feels very smooth again which seems to endorse Peter's comment about gearbox bearings causing much of the vibration felt throught the gear stick.

Bernie.
b higginson

Peter,

I have a 'Scientific Balance' that I sourced from a Biochemistry Lab several years ago. And yes it is enclosed. :)
Deborah Evans

Deborah

Why do you feel the need to balance to less than 0.1g?

I just weighed a set of 8 big end bearings from an MGB they weigh:
18.3
18.4
18.3
18.3
18.3
18.4
18.2
18.2

An A series follower went from 42.6 to 42.7 with 3 drops of oil from an oil can, when the rods are in the engine and oil is splashing about surely the within 0.1 must 'go out the window'?

Peter
P Burgess

I do have accces to 'Scientific' scales but have now only roughly measured on the kitchen scales ( amazingly constant on repative measurements)

But the bearing weight etc argument gave me my answer.
I need not to worry!

Just need to clean them up then.
And start thinking about converting to fully floating or not....
Onno Könemann

Hi Onno

have you ever used Teflon buttons?(not on your coat!)We tend to use press fit as it is one less 'thing' to go wrong :)

When we use Carillos or Arrows we have no choice but to use the slinky spiral spring retainers which are great fun to fit....I check them loads of times as I am paranoid I haven't locked them fully home!

Peter
P Burgess

Peter,

I should have said balance to +/- 0.1g, NOT within 0.1g. Sorry, too much vino tinto last night!

I do it for a number of reasons, firstly because I can and it offends me not to. Secondly, as you are aware, I have been building Climax FW Series race engines for around 25 years (and NEVER had one of mine go 'pop').

Back in the old days I was friends with the two Climax tuning gurus: Ian Carter and Andy Chesman (both sadly long since deceased). Both told me that's what they did so I followed suit. Anything you can do to protect the bottom end of an engine that turns at 9500 - 10500 rpm is a good thing in my book!

I wouldn't do it on a stock road going motor because I don't (or rarely) build such things.

I do it on Fast Road Triumph 1500s because, again, anything you can do to help their bottom ends is essential for reliable power.


I'm intrigued as to the weight variance in the big end shells - The ACL Duraglides and Clevites that I use have never shown such variance (maybe I've just been lucky :) ).


I'll grant you that oil splash will alter things but surely that is a Dynamic and ever changing effect that we can't control (other than using a Windage plate (which all my race motors have) and/or Dry Sumping (which all my Climax race motors have).




With regard to fully floating vs press fit gudgeons I favour the latter for reliability (no circlips to bounce out at high rpm), but I favour the former for the fact you don't have to destroy a piston in order to get it off the rod! I rather like the teflon button idea but can't always seem to find the size I want.
Deborah Evans

Hi Deborah TBH I was not aware you have built Climax engines for 25 years I first heard your name a year or so back on these threads associated with 1500 engines.

Peter
P Burgess

When I started off I was in the RAF so I did it for myself and those friends who had them for a few wine tokens.

I do it professionally now because:

a. I have a Ginetta G15 racer.

b. Aside from Reg Patten (ex Imp Service) there is NO ONE I trust to do the job well (no names, no pack drill).
Deborah Evans

I am thinking about FF because of reliability issues!
Have seen wat as press fit pin does to the cylinder wall after slowly walking out.
Not a pretty sight.

I would think teflon buds would not be that hard to make on a lathe?
So that would just leave me with a set of rods to bush and ream to fit anny piston i like right?

The circlips just looke scarry to me
Onno Könemann

I used Teflon plugs for years, easy to machine and never a problem.
Paul Walbran

Great
Any types of teflon to use (or is there just one grade)
And do they wear out or when to replace them?
Onno Könemann

Hi Onno


Not a clue, you need to research and await some good advice on these threads and other threads? We have only used a white teflon for bushing purposes but not used it in anger in engines.

Maybe Paul can illuminate the subject so you can make some?

Here is a link to some from Jonspeed on ebay ....seem pricey if nothing special IMHO :)

http://cgi.ebay.co.uk/Classic-Mini-1275-Teflon-buttons-set-8-/140274484394?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item20a902c4aa

I know what you mean about gudgeon pin creep but it seems to be poor fitment rather than a 'natural' process.

Peter
P Burgess

This thread was discussed between 06/07/2011 and 08/07/2011

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