how to DIY balance crankshaft and flywheel (BMW fan on 4 cylinder TRs)

[Z320]

Issue: engine, no special model.

 

Hi there,

is there a way to DIY balance chrankshaft and flywheel bolted togetter?

Who did it?

Ciao, Marco

Edited January 3, 2020 by Z320

[spyder dryver]

Hi Marco.  I'd leave it to the experts. An incorrectly balanced crank/flywheel could easily wreck your engine. A detached flywheel could chop your feet off! 

DIY balancing must be near enough impossible. I'd be amazed if it can successfully  be done at all without proper professional equipment. 

It doesn't add much to the overall cost of an engine rebuild either. 

[john.r.davies]

Static balancing could be achieved on a pair of knife edges, but that's not enough.

It needs to be dynamically balanced by spinning it, sensing the moments that are induced and repeating after unweighting the appropriate part(s).     That requires a specialist rig and lot of experience.

John

[Nigel Triumph]

DIY balancing of reciprocating parts, i.e. pistons and conrods is possible with care.

As has been said above, balancing rotating parts, crank shaft and flywheel, requires special equipment and expertise. DIY attempts could even be dangerous. Don't forget to include the front pulley when balancing the crank.

However, the results in terms of smoothness on the long stroke 2500 engine are well worth the expense.

Nigel

[Z320]

Hi all, 

thanks for your answers.

Has the crankshaft been balanced by the Triumph factory?

If I change noting - do I have to balance it again?

What do I have to tell the one who does this?

On YouTube I've seen they put weight on it instead of rods and pistons.

What I forgot to tell is - I own a "Hofmann Finishbalancer" for dynamuc balancing wheels on the car. 

Could be a little bit of effort- but a challenge....

Ciao, Marco

 

 

 

[ChrisR-4A]

Great stuff, but if you go to the trouble of having the crank, rods, pistons, flywheel and clutch balanced don’t forget the prop shaft. They were balanced originally by Triumph but that was a long time ago.

Also on a 4cyl TR either remove the fan and long extension and go electric or include these items to be balanced. That awful extension is frequently out of Ballance and I have seen many which due to errors in mounting run far from true.

Chris

[spyder dryver]

All cranks are balanced from the factory, some likely better than others.  During my recent engine build, a 1995 Toyota 3SGE 2 litre, I insisted on crank and flywheel balancing, despite being advised that it wasn't necessary. Guess what? It wasn't necessary! The crank came back with two tiny, tiny drilled dimples. One was little more than a dot punch mark. The flywheel had just one tiny dimple. A 60's crank may benefit though.

Bobweights are un-necessary on a inline 4 pot. Or an inline 6. 

 

[Bfg]

2 hours ago, Z320 said:

Has the crankshaft been balanced by the Triumph factory?

If I change nothing - do I have to balance it again?

What do I have to tell the one who does this?

On YouTube I've seen they put weight on it instead of rods and pistons.

The crankshaft has been balanced by the factory (see photo) and, when cleaned out inside, the only reason for that balance to have changed (aside from the crankshaft being bent !) would be in the crank-pins journal size.  And even though most of that (up to 0.0060") ground off the journal is countered by (similarly +0.060") white metal in the big end shell.. there would still be a difference.  I might only guess a 0.010" big-end regrind would hardly be noticed in the balance.

Likewise the flywheel was balanced at the factory.  You'll see this a hole, or perhaps two, drilled part way through on the same pcd as the clutch fastening holes. 

Of course - the flywheel may have been changed sometime through the years, &/or else perhaps the clutch was from Laycock rather than Borg & Beck ..or vice versa (each will have a different rotational mass).  When balanced together their dynamics would be different. 

My understanding is., the operator will also require the clutch cover and its fastenings, the pulley, extension and fan if you are using a mechanical one + their fastenings, and one of the con-rods and pistons, complete with its bearings and fastenings.  He will not use that on his machine but will need to accurately weigh them, and to program this into the overall balancing equation.  If you are planning to do so then it's best to match-for-weight the sets of piston to conrods, so they are all the same.  That is something you can easily do at home yourself.  The operator might also like to know the intended state of tune of that engine,  ie. compression ratio, type of camshaft, etc.

Hope that helpful.  Pete. 

 

Edited December 22, 2019 by Bfg

[Z320]

17 hours ago, ChrisR-4A said:

Also on a 4cyl TR either remove the fan and long extension and go electric or include these items to be balanced. That awful extension is frequently out of Ballance and I have seen many which due to errors in mounting run far from true.

Chris

Hi Chris, 

my TR4A still runs with the fan and extension, that's fine,

but with the red plastic BMW fan, with the TR original the engine rund like a sack of nuts!

The workshop manual mentions to balance it but I failed with that!

Ciao, Marco

[Z320]

 photos deleted because of not enough database

 

 

Edited May 23, 2020 by Z320

[john.r.davies]

Marco,

Even in a photograph, your vertical centre line is way off.

JOhn

Edited December 23, 2019 by john.r.davies

[Z320]

Hi John,

the plumb line was upright, I checked that several times.

For shure I did not hold the camera  absolutely vertical.

If you like turn the photo until you got the  plumb line vertical.

Sorry for that irritation.

Anyway the weight center of my fan is horrible out of the drill center.

Ciao  Marco

 

[Mark69]

If you run the plumb lines from tip to tip rather than middle of blade they centre better.

[Z320]

It will make no difference,

from any pivot piont the plump line always goes though the one and only weight center.

This works in every position you hang it up.

But I may be wrong...?

 

Edited December 25, 2019 by Z320

[Bfg]

just playing around . . 

^ as you can see I've not cleaned this 'tropical' fan at all, and it has part of its blade is missing. This and other blades were bent (see below) but I did tap those generally straighter with a hammer.  A flat magnet (used for tool spanners from) is a convenience balance to move up and down the steel hub, until it sits there balancing on the point of a bradawl ..which is centred under the slightly domed cap (formerly from a calor gas bottle, whose the inside's centre was clearly defined). 

I did very shallowly drill it at that centre ..to a very shallow inverted-v.   But that was only so that I might easily position the cap on the bradawl and so it didn't slide of centre as I adjusted the balance weight on the fan itself.  Anyone with a lathe might very accurately turn an inverted V in a similarly lightweight material instead of using an old screw cap.?

 

^ This is as taken off,  with corrosion, bent blades and an odd arrangement of locking washer.  Of course these fastenings, the fan extension, and the pulley would also need to be in balance too. 

Pete

p.s.  this fan weighs 922g.  I see yours weighs more was that including fastenings and lock washers ?

Edited December 26, 2019 by Bfg

[Z320]

Hi Pete,

1105 gramm is its weight as shown on the photos.

I had the BMW fan already on the engine when I bought the car.

The original one was a present from a friend who  changed over to the BMW fan.

When I compared the BMW fan was much lighter, I remember about only 250 gramm,

the engine run very bad with the original, that really hurt me through and through,

and with the engine ideling (like on Stau) with a anemometer the BMW fan had about 50% more ventilation.

3 good reasons for me to store the original and further drive the BMW fan.

Ciao, Marco

[Bfg]

In summary ; your TR4A has a plastic blade BMW fan which is

1. about 250g in weight, and
2. the engine runs much smoother with it, and
3. there is much better air flow at tickover engine speeds.  ( I presume then it is not a viscous fan ).

Might I ask what fan this is  ?  ..and what needs to be altered to fit it ?    I guess you also use a narrow fan-belt conversion from one of the usual suppliers.? 

As the fan extension on the TR4 is about 114mm long (if I remember correctly) and cast iron ..it and its central bolt weigh quite a lot.  Has anyone replaced this with an aluminium one. I would have thought that quite easy to make if one has a lathe. 

Thanks, Pete 

[Z320]

1st: Yes, much lighter, please don't fix me on exactly 250 gr

2nd: Yes, probably mainly because the original is badly out of center

3rd: Yes, yes it us solid

It's from the classic BMW 1502, 1602, 1802, 2002, 

browse for "BMW 1255505", very popular on lots of german TR 4 cylinders.

It's red, no bad idea for a fan, I've been told the drills fit but have to be made to a wider diamter.

This is the case on mine to fit there 4 steel bushed to avoid to squeeze and crack the plastic.

Ciao, Marco

edit, sorry:

I use the standard type "20" belt, but more flexible because theeted, a Flennor 20X900,

currently a Gates typ "17", also theeted

Ciao, Marco

Edited December 27, 2019 by Z320

[Z320]

Good morning Pete!

Please see this english post

Two thinks I have in mind, but no time for that:

- make my own fan extension with less weight, I have seen that on a TR some years ago

- make a housing around the fan to limit loosing air thrown radial, this has been discussed at the german TR forum (but no one did it?)

Ciao, Marco

Edited December 27, 2019 by Z320

[Bfg]

Thanks Marco.  I see these "BMW" fans from Latvia ..but I guess they are copies. 

I think I will look for a genuine BMW one, where I can trust the material it is made of.  I would not want the fan to disintegrate when spinning at speed and damage the radiator, the bonnet, or me !  (..peering in to see what that noise is).

Pete.   

[Andy303]

15 hours ago, Z320 said:

1st: Yes, much lighter, please don't fix me on exactly 250 gr

2nd: Yes, probably mainly because the original is badly out of center

3rd: Yes, yes it us solid

It's from the classic BMW 1502, 1602, 1802, 2002, 

browse for "BMW 1255505", very popular on lots of german TR 4 cylinders.

It's red, no bad idea for a fan, I've been told the drills fit but have to be made to a wider diamter.

This is the case on mine to fit there 4 steel bushed to avoid to squeeze and crack the plastic.

Ciao, Marco

edit, sorry:

I use the standard type "20" belt, but more flexible because theeted, a Flennor 20X900,

currently a Gates typ "17", also theeted

Ciao, Marco

Marco, By "theeted" I presume you meant "toothed" or gezahnt?

Thanks to google translate: https://www.google.com/search?client=firefox-b-1-d&q=google+translate

English "tooth" and German zahn have the same "roots" (there is a pun there):  https://tinyurl.com/wu4utwp

Many thanks by the way for your many useful and informative posts.

Andy

[Z320]

Hi Andy,

indeed you are right, that's what I mean.

And indeed my english is a little bit weak, I work on that....

Ciao, Marco

[Z320]

Ups,

by accident I bought another BMW fan

from a reliable TR supplier for some experiments.

I will report on another post.

 

[BlueTR3A-5EKT]

On 12/27/2019 at 11:33 AM, Bfg said:

Thanks Marco.  I see these "BMW" fans from Latvia ..but I guess they are copies. 

I think I will look for a genuine BMW one, where I can trust the material it is made of.  I would not want the fan to disintegrate when spinning at speed and damage the radiator, the bonnet, or me !  (..peering in to see what that noise is).

Pete.   

In which case you need to adopt the genuine Standard Triumph engineering test 'BOW'.  The factory had issues with fan blades snapping when plastic fans were adopted

.  They developed the BOW test

Bucket  Of Water.   You threw it at the radiator and onto the fan when the engine was running at 2000 rpm.   This simulated hitting standing water on the road or passing through a flood.    

Two issues arise if the fan is of the wrong design or material.

1.  A blade breaks

2.   The blade tips bend forward and touch the radiator core.

This was described to me by Tony Lee the former Triumph Experiment shop manager in the era of TR3 Beta, when I met him at STIR

Cheers 

Peter

Edited December 31, 2019 by BlueTR3A-5EKT

[stillp]

I heard of the BOW test in connection with the Rover 3500 - lift the bonnet, empty the bucket of water over the engine, count to ten - if any water has reached the floor by then, you've forgotten to fit something.

Pete