DarrenW
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| posted on 20/11/06 at 09:28 PM |
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Engine Balancing
Has anyone done it themselves? How did you do it. Im not thinking full dynamic balance here - more of a half balance of con rods and pisons. Can it be
done at home? what measuring equipment? Where is material removed from? Anyone have some specialist for borrow / hire?
Just interested at the mo. I know pro job will always be preferential but there must be so much that can be done from first principles at home. Been
offered a 40K mile std injected engine. Thinking it wont need any rebore / regrind, stripping it down for inspection and basic internal work could be
on the cards. Ive also got chance of BV head to make it all work.
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flak monkey
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| posted on 20/11/06 at 09:33 PM |
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You can do it with a pair of digital kitchen scales.
You can balance the conrods and pistons fairly easily. Usually do them as a unit, unless you really want to separate them.
Material is removed from the gudgeon pin boss on the underside of the piston to balance them. They all need to be within a gram or 2.
If you have seperated the piston and conrod, you can balance the gudgeon pins by removing material from the inside of them. And the conrods need doing
one end at a time, so you will need to make up a pivot bar to do it.
The crank and flywheel can be balanced manually using a grinding wheel balancer, its a long process though. And is far better done dynamically.
Apparently the pinto engines were pretty well balanced as standard.
If you are going to ditch the head from your injection enegine, let me know!
David
[Edited on 20/11/06 by flak monkey]
Sera
http://www.motosera.com
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DarrenW
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| posted on 20/11/06 at 09:46 PM |
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Thanks David,
After posting i decided i should ask another question - why bother on a std bottom end that is factory stock. Ive just thought that probs the main
reason to have a aftermarket rebuild fully balanced is that the new parts will be manufactured to aftermarket tolerances. From experience i know these
are rarely the same as OEM specs. Factory engines will be balanced on very very expensive equipment as part of the process. Hence stripping and
cutting will negate all o fthis so it is sensible to get you rrebuilt motor balanced as a matter of course.
So - to turn this thread on its head early on - would anyone expect to be able to get a minimal use stock motor any closer / better balanced at home
than it was in factory?
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mookaloid
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| posted on 20/11/06 at 09:56 PM |
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I think that factory engines are built down to a price and are subject to mass production variation tolerences.
A carefully hand built motor by someone who knows what they are doing with attention to detail will always be better than one built in a factory.
Hence a 'blueprinted' engine with closely matched parts will be considerably more powerful than the same engine with nominally the same
components as the factory one
Further if you try to rev a standard factory engine past it's expected limit in normal use you will probably damage it. If you want to get more
than standard power you have to pay more attention to it as you are exceeding the original design parameters.
So dynamic balancing will help an engine if you are revving it to 8000 rpm when it's original specification was only 6000
Cheers
Mark
"That thing you're thinking - it wont be that."
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mark chandler
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| posted on 20/11/06 at 10:13 PM |
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I,ve done it, engine seemed pretty good at the time !
Lumps like pistons and con rods should all the same weight relatively, so make them all equal the lightest one, I just used a simple balance, like a
coat hanger really that you dangle the bits off.
For the crank a couple of straight edges that are horizontal, the crank will find the low point, then add pulleys and fly wheel.
When building shortest rod with longest piston (pin to crown) to match as much as possible, then when you assemble swap around until they are the best
match to the top of the bore (equalise the crank throw).
Measure the combustion chambers, if its a pinto then make sure all valve collets are the same hieght as this affects cam timing, you may even need to
recut a couple of valve seats to balanace them up!
Regards Mark
[Edited on 21/11/06 by mark chandler]
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DarrenW
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| posted on 20/11/06 at 10:34 PM |
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Thanks Mark,
So you basically got the parts equalling the same weight. If i did it id probs leave rods and pistons connected. All equal is better than nowt. Hard
part is finding scales that split grams. Please explain the coathanger method more.
Crank sounds like a simple grinding wheel balancing jig. In terms of material removal id probs grind it off balance weights with die grinder or off
split lines. I know the principle is that you should be able to rotate crank into any position and it will stay put without rotating. Brings me back
to my toolmaking days.
Did you find there was much to remove.
Is it in all honesty worth the gaskets and bolt costs? and i guess also the risk of damaging something. Other option is to take parts to local
specialist and spend £90 or so. And also £50 getting flywheel lightened. Is £140 therefore money well spent or have a go at home.
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pajsh
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| posted on 21/11/06 at 08:33 AM |
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I stripped mine at the weekend with a view to getting the flywheel lightened and crank/flywheel/clutchplate balanced as a unit.
I took the pistons out as I intend to get the block skimmed and cleaned up but dropped piston 4 when I took it out.
Bu66er!.
No visible signs of damage but I guess it's not worth the risk of re-using it.
Guess I may have to get a new one now and might be tempted down the 2.1 route that I was trying to avoid.
I enjoyed stripping it down though and I've learnt alot so well worth it.
I used to be apathetic but now I just don't care.
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DarrenW
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| posted on 21/11/06 at 09:43 AM |
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All interesting stuff. I know there are various levels of balancing depending on size of wallet. If we talk about the job you would expect for 90 -
120 quid as part of a 6or700 quid 2.1 rebore job - what exactly would the engineering shop do for the cash?
ie would you expect conrods balanced end to end, pistons matched to within 1 degree, pins matched, all 3 bits assembled then checked for variation.
Crank, pulley, flywheel and clutch plate balanced.
Would they then assemble con rods to crank and balance that up as well?
Or is listed above more than the average balancing job???
ive also heard the terms static and dynamic balance mentioned. In terms of the engine do i assume static is similar to balancing a grinding wheel - ie
on 2 level knife edge plates - and dynamic is crank assembly on special machine that will rotate it (just like a Schenk balancer).
The other question - if you got a very low mileage Pinto, never been apart before. Stripped it down and found rings, bearings, bores, pistons etc were
all perfect and well within tolerance - would you change them anyway or take a chance??????? Im just wondering if its worth paying for pro balancing
job but keeping to seriously low budget.
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bimbleuk
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| posted on 21/11/06 at 09:50 AM |
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Toyota are supposed to be particularly good a factory balancing their engines. The blacktop 20V 4AGE has lightened internals and is allegedly balanced
to 9000RPM!
Saying that I just got a 20V head back from being modified and there were a few things which could have been better. The valves were machined very
slightly oval and the deck was also a few though different at either end. So yep I would say you can always improve an average production engine. The
labour cost though is way beyond mass production requirements. I know after receiving the bill for my head!!
So even though I've already built the bottom end with new bearings etc. I'm probably gonna strip it back down and get it balanced
properly.
I've had this done twice before and every time the engines (16V 4AGE, 1.8 K series) have been noticeably better for it.
[Edited on 21/11/06 by bimbleuk]
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02GF74
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| posted on 21/11/06 at 09:56 AM |
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coat hanger method - what I think this is saying you have a bar that pivots with say two hooks. the bar is adjusted to be hotizontal then by
attaching items to the hooks, the heavier item will tip it to one side so you need only know which one is heavier and not their actual weight.
Obviously you find out the lightest one before you start matching.
There is a method of balancing the rods that ionvolves bolting 2 side by side so the litte ends points outwards then putting the arrangment on an adge
and seeing which way it tips - somtewhitng like that - I'll need to look this up to find out how exactly it is done and what it achieve but if
memoruy serves me well, it is a step towards dynamic balancing.
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NS Dev
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| posted on 21/11/06 at 12:42 PM |
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Right, in your position Darren I would do the following (I think! )
Balance the rods and pistons yourself, of course not so easy if you are keeping the existing pistons, but get the crank, pulley, flywheel and clutch
cover dynamically balanced.
Ideally (again needs to not have pistons attached! ) you want to clean the rods up, deflash them etc, then balance them, then give them a light
polish, then shot peen them.
Certainly factory std balance on any pinto is suspect, and for higher revs needs looking at
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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CairB
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| posted on 21/11/06 at 01:02 PM |
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A crank, or any shaft, can be in static balance but not dynamic balance.
If you imagine that you have a shaft on bearings with a wheel at either end, each with weights on opposite sides of the wheel, say at the 12 oclock
& 6 oclock positions.
Statically this would be in balance as it would stop at any position and stay there,
assuming the offset masses are the same.
Now imagine rotating the shaft. The offset masses will now cause a moment down the length of the shaft which gets larger with increase in speed, by a
square law.
To balance the shaft to reduce the moment and therefore the bearing loads due to out of balance, mass must be added or subtracted at specific angles
and distances down the length of the shaft.
This is dynamic balancing.
Hope this helps and I haven't confused
Cheers,
Colin
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02GF74
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| posted on 21/11/06 at 01:39 PM |
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as wot CairB said. ... depends where the weight is sitting; say you can prepare piston/con rod combos to be the same wieght but if one piston was much
heavier but had a lighter rod, then you'd get vibes.... and the further the weight is from the centre of rotation, the worse it becomes.
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ned
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| posted on 21/11/06 at 01:45 PM |
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A mate of mine built his own 'standard' pinto and balanced all the bits to within a gram on a digital set of mini/kitchen scales. he has a
lathe so also decided to turn a bit off the piston skirts to lighten them all and turned a bit off the flywheel iirc. Engine didn't make as much
as the pro engines but made more than it did beforehand..
Ned.
beware, I've got yellow skin
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DarrenW
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| posted on 21/11/06 at 02:38 PM |
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Thanks again for the advice. I had already thought how the static balance could work - ie you can determine the heavy side when rested on knife edges
but where to remove or add material along the length is totally unknown.
Thanks for the practical experience feedback Ned.
In reality what i will probs do (if i buy it) is fit low miler bottom end and dont touch it. Concentrate on ignition and fuelling. Lighten flywheel.
Possibly port head some more. Then get old 205 block rebuilt at a later date and swap it over one weekend.
Your posts are helping me to understand how engines are balanced / confirm what i thought.
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02GF74
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| posted on 21/11/06 at 02:42 PM |
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quote:
Originally posted by DarrenW
- ie you can determine the heavy side when rested on knife edges but where to remove or add material along the length is totally unknown.
if in doubt, remove weight furthest from the axis of rotation.
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NS Dev
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| posted on 21/11/06 at 03:15 PM |
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quote:
Originally posted by DarrenW
Thanks again for the advice. I had already thought how the static balance could work - ie you can determine the heavy side when rested on knife edges
but where to remove or add material along the length is totally unknown.
Thanks for the practical experience feedback Ned.
In reality what i will probs do (if i buy it) is fit low miler bottom end and dont touch it. Concentrate on ignition and fuelling. Lighten flywheel.
Possibly port head some more. Then get old 205 block rebuilt at a later date and swap it over one weekend.
Your posts are helping me to understand how engines are balanced / confirm what i thought.
That sounds like a good plan Darren. You can then remove the old pistons from the rods (out of the old block) and prep the rods properly (bore and fit
bushes, end for end balance after deflashing and lightening, then smooth/polish and shot-peen) then you can fit aftermarket pistons with floating
gudgeon pins, job then being a much better one!
Nowt to stop you doing the head to some extent on the std bottom end, only probs will be valve to piston clearance really depending on cam choice,
plus you'll need to keep the revs down of course.
All of that said, 145hp is no probs on a bog std bottom end, I've done it on our old road rally car, and we never blew the engine despite lack
of rev limiter. Never had a rev counter on it either lol  and it had double valve springs and 285 cam so it revved out okish. To be honest I think
the 38 dgas carb was the limiting factor, but it would certainly beat my 2.9 XR4x4 in a straight line.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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DarrenW
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| posted on 21/11/06 at 03:46 PM |
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Current head is already injection type that has been diy ported following Des's recommendations to a point. Ive had 40thou skimmed off. Ive
revved it out to just over 6,500 before and its ok ish. Might as well get flywheel lightened whilst engines out.
Ive also got the chance of a nice BV head with 44.5 inlets and 38 exhausts. Bronze guides, double springs etc. Apparantly it helped a 2.2 to record
202bhp at flywheel. FR32 is way too tame for it tho and ill have to learn about valve train geometry to set it up. Its not hardened seats which doesnt
worry me too much - surprisingly most BV heads arent, must be to do with the amount of material that is removed and no-one wanting to pay for extra
seats to be added. £200 sounds a bit steep but if its a good one suppose its OK. I was quoted £200 just to port mine with std valves.
I reckon 38 DGAS is also my limiting factor. Ive never had it set up properly. Bike carbs and megojolt must give me another couple of hp.
Ill be able to get the old lump rebuilt in stages at my leisure and look out for ebay bargains (eg V6 pistons etc).
Im a bit narked that funds have forced the rethink but at the end of the day its only a hobby and my family always comes first. It is good though in a
way cos its stopping me from sinking too much cash at once and doing things the hard way rather than getting the card out!
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DIY Si
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| posted on 21/11/06 at 04:11 PM |
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If you do get ahead without seats in it, make sure you use good lead replacement stuff, as I used the Castrol (?) stuff from halfrauds in my mini, and
it nearly ate the exhaust valve seats straight out the back of the head inside a year. I've been told the aldon stuff is the best, but
it's that potent you have to go get it as no-one would agree to courier it!
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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akumabito
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| posted on 21/11/06 at 06:01 PM |
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..would it be possible to lighten the internals of an engine yourself? How much weight could you safely remove from pistons and rods?
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DIY Si
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| posted on 21/11/06 at 06:05 PM |
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Given some sensible metal removal, yes, perfectly possible. Some of the tuning books give diagrams about where to remove and how much. Dave Vizards
book on the A series is good for this. Less good for a ford engine though!
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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