balancing/blueprinting the bottom end

Post by **alainmoran** » Mon Jul 27, 2009 10:12 pm

Well I finally got round to swapping out the spare engine for the decent one, and maaan I thought that the bottom end was a little rough on the spare, but given the difference in sound I'm suprised it worked at all!

So, this means that the bottom end will need replacing on my spare engine, and while I'm at it I'm interested in blueprinting it ... are there any vendors who can supply matched pistons, rods etc...

Has anyone out there done this before and can they give me their advice?

Post by **bmcecosse** » Mon Jul 27, 2009 10:48 pm

Well - I used to do it with my competition Mini engines. If you buy - you will pay a fortune ! I have to say - for road use - this is not going to make any great odds - but - it is quite satisfying!
First -weigh the pistons - you will need an accurate digital scale - and decide if you want to reduce their weight (I used to machine off most of the skirt!) - and then gently file away at the base of the heavy pistons - until they all weigh the same. Then - conrods. You need to weigh each end of the rods - so to do that you need to suspend the 'other' end with a thread hooked over a suitable stand -so the rod lies horizontal with the end on the scale pan. Note the weights - file off from the heaviest until all the 'big ' ends weigh the same - then do the same for the 'little' ends. That's sort of 'stage 1' balancing. To get nice even compressions - you should assemble the engine - and turning each piston to the top in turn - note how far down the bore each piston stops - from the top of the bore. If there is a variation - you would need to skim the block to put the furthest down piston flush with the top - and then skim the other pistons until they too are flush. Of course - this will mean each piston now has a slightly different 'dish' - and so perfectionists will machine each piston top to make them identical! The pistons will then need balancing - as before. The cylinder head will need skimming - and then the volume of each chamber carefully measured (with burette - filled with paraffin/oil blend) - and again the volumes equalised by carefull grinding. This would be 'stage 2' balancing. It ignores any possible slight variation in the length of the con rods, and in the stroke of each section of the crank. Generally - these are correct to fine limits anyway. The rotating assembly - crank/flywheel/crank damper - can also be lightened - and dynamically balanced - but that needs specialist equipment and is not cheap. I have simply 'statically' balanced a rotating assembly - by fixing two long silver steel rods to a machine bed - so they overhung the edge and were perfectly horizontal. I then laid the asembly on the rods - on it's main journals - and it rotated and settled at one point. Marked the heavy spot with chalk - repeated several times - it always settled same spot. So - drilled a 1/4" hole in the flyhweel rim (inside the ring gear!) at the heavy spot - and repeated. After a few holes (about 4 as I remember) - it showed no special preference for settling. That assembly revved to the heavens in my Competition Mini !

Post by **LouiseM** » Mon Jul 27, 2009 11:17 pm

I think this is your longest post yet Roy. Careful you don't get RSI

Post by **alainmoran** » Mon Jul 27, 2009 11:19 pm

Oooh .. ty .. I didnt realise that you could machine the parts down, but that's an excellent idea, I could quite possibly reuse the parts I already have, assuming they arent already shafted (the engine really did sound like a bag of nails)

Yes, the idea of balancing the engine is more for fun than anything, I want to have the experience of having done it ... also the engine should run sweet when it's done which will be nice

How accurate is accurate? ... are we talking thousandths of a gram here, or just hundreths?

Would it be worth waiting to balance the pistons until after I've skimmed the block, seems a shame to do all that work weighing them to just have to go through the whole process a second time?

Post by **bmcecosse** » Mon Jul 27, 2009 11:32 pm

Yes indeed - only balance them once. The first part is just the 'stage 1' balance. I would say 1st decimal place in grams will be fine ! I dare say Mclaren are slightly more fussy with Lewis' engine - but it dose rev to 18000 !!Ideally - you would buy 100 pistons - and select the 4 lightest ones with the same compression height etc etc. Same with con rods - and agin with the crank - looking for one which has top limit stroke length. This would be true 'blue -printing' - selecting componts that are right at the top (or bottom) limit of the sizes given in the 'blue-prints' - to maximise the engine power output, but still using 'standard' parts.
You should chase up a Vizard book on the A series - always plenty on ebay.

Post by **mike.perry** » Tue Jul 28, 2009 12:33 am

Having run the big ends in my side valve engine and therefore requiring a rebuild I was considering some added tuning possibilities, balancing being one option. It has been converted to unleaded with hardened valves, guides and inserts and polished ports. It has a lightened (but probably no longer balanced) flywheel, a reprofiled cam in a spare engine, and probably a higher than standard C/R. Any recommendations for upping the present 35 odd BHP without bankrupting myself in the proccess?
1st stage is probably a decent exhaust manifold.
I don't intend going the Alta way but if anyone has a spare Derrington head!!!!!!!!!

Post by **bmcecosse** » Tue Jul 28, 2009 9:32 am

Balancing really only pays off if intending high revs. Compression Ratio is everything - I can't remember now if it's possible to grind the head of a side valve - without the valves touching the head. Re-profiled cam sounds interesting! If it has higher lift - again check for collision. Biggest first step will be a much better inlet manifold - and either bigger single carb - or twin carbs feeding each port directly. Probably possible to improve the flow in the ports too - but again it's 45 years since I worked on a SV engine - so can't now remember the inlet path. In those days - we were just happy if it started!

Post by **Alec** » Tue Jul 28, 2009 6:38 pm

Hello all,

blueprinting is a time consuming job and expensive if you have to pay a machine shop. Other things not mentioned are making sure the crank journals are exactly the correct angle apart (180 degrees for a Minor) and equal throw. Cylinder head work. ensuring the valves are all equal in height above the head and that all the springs have equal pressure (corrected by shimming the springs) Camshaft, similar thing etc.

An interesting book on car preparation is one written by Smokey Unick (sp) as he was very fastidious. When he bored a block he clamped a thick piece of metal instead of the head (with holes in, obviously) and torqued to the head setting. This meant that when he bored and honed the block, any distortion due to the stress of the studs was automatically corrected and gave a truer bore.

Have fun.

alec

Post by **MarkyB** » Tue Jul 28, 2009 7:16 pm

If that's all Smokey Yunick did he was slacking. Stage 2 is to heat the block up as well before boring it so everything is spot on when it's up to temperature.

Post by **Alec** » Tue Jul 28, 2009 9:16 pm

Hello Marky,

that's a new one, but metalurgically, what's the difference between say 20 degrees C and 80 degrees C?
I see you did better with his surname than I, he was a very highly regarded and original thinker in improving his cars' performance.

Alec

Post by **MarkyB** » Wed Jul 29, 2009 7:22 am

Google suggested the right spelling for his name not me

.
I'm no metallurgist, is the answer "the amount of expansion?"
He does sound like quite a character and innovator.

Post by **RobThomas** » Wed Jul 29, 2009 10:16 am

Many a happy hour wasted on this crank. Then it blew the rear main bearing cap off and wrecked it. Lesson? Making it run is cheap, making it run really well can be veeeeery expensive.
I'd never bother to do it again for a road car since the return for my time was not worth it. Getting the flywheel balanced with a new ring gear might be a good idea, though.
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Post by **alex_holden** » Wed Jul 29, 2009 12:41 pm

RobThomas wrote:it blew the rear main bearing cap off

What kind of revs were you doing at the time?

Post by **alainmoran** » Wed Jul 29, 2009 4:00 pm

RobThomas wrote:the return for my time was not worth it.

Hmm ... interesting ... I'm personally hoping that by balancing out the engine it will become more efficient (lower fuel consumption) and last longer (less stress on bearings etc) ... My minor will never be a quick car, but it would be lovely if it sounded like a sewing machine!

Post by **RobThomas** » Wed Jul 29, 2009 4:30 pm

Alex.
I'd given the car a good spanking after visiting a rally at gaydon. I was going down the M5 and stopped at the M50 services when it started making funny noises and the oil pressure light/buzzer came on (set at 25 psi)
The threads had pulled off the main cap bolt on one side and the whole cap became loose. I found that the bolts were a poor fit in the block but that new bolts were much closer fit. Maybe they'd been overtorqued or had had a tap run up them before I got it.
The tip I learnt was to spend money on new ARP bolts or to replace the cap bolts with new ones. The type of bolt head shown in the photo have a special design that has a convex undersurface that can flex andtake up slack if there is any vibration rather like a spring washer in a looser arrangement. It thus damps any loads put on it (So the book says)

Post by **bmcecosse** » Wed Jul 29, 2009 4:30 pm

Why on earth did it 'blow the rear main bearing off'?? Not heard of that before - even on some VERY fancy Mini engines ! Not seen a crank worked like that either - 'blading' and 'wedging' yes - but not machining all over !

Post by **RobThomas** » Wed Jul 29, 2009 4:48 pm

If I wanted to get the smoothest engine that also ran at the best economy then I'd get the largest capacity I could (+60) and skim the head to get the highest comp ratio I felt I could live with (10:1?)
The breathing would be the next obvious area and that means a Mini manifold and HS4 carb (12G787 rings a bell) or even better would be a tubular exhaust and a small bore alloy manifold (not MG Metro) that was then sent to a rolling road session (£80+) for the correct needle and timing curve. If I had more funds then maybe a cam change to MG Metro spec or the Swiftune SW5?
Having spent over £2000 on an engine rebuild in the past I think I'd have had more bang-per-buck by a change to a Rover K-series.

I'd recommend several weeks reading the Vizard book to see just how many free horsepower you could get for yourself without much effort. Best money saving tip of the year!<br>

<br>

Post by **bmcecosse** » Wed Jul 29, 2009 4:59 pm

You'll want a bigger carb than the HS4! HIF 44 is more like it - or, better still - 2 X HIF 44 on good tubular 'weber like' manifold - ie NO balance pipe. Cam change is pretty much essential - MG Metro is good if you want torque and max ~ 6000 rpm. 544 is better, less low down 'torque' - but 8000 rpm if you want it!

Post by **mike.perry** » Wed Jul 29, 2009 10:17 pm

I'm after max low speed grunt with the MM s/v engine. It's no good pulling a trailer up a hill with no power under 3000 revs. With a 57 x 90 bore / stroke and 4.55 diff it is pulling 4000 revs at 60mph. Max power is at 4400rpm. Anyone care to calculate the piston speeds? I think that aiming for a 60mph cruising speed and 70 max with good hill climbing ability is the way to go

Post by **bmcecosse** » Wed Jul 29, 2009 10:58 pm

It's crying out for a supercharger!
I doubt you will get 10:1 comp ratio by skimming the head - without the valves hitting the head - and the big-end bearings melting like chocolate!