Bottom End Balancing/lightening Advice Please

[Rob205 1]

Hi,

 

Can anyone out there help me please?

 

My goal is to have a 205 1.9 Gti 8v engine built for road use only and as such I want tractability and smooth delivery over ultimate power, so no wild cams or carbs. So far I’ve got a head skimmed with triple angle valve seats cut retaining the standard valves however I‘ve now got to move on to sorting the bottom end.

 

As such I’ve been researching lightening and balancing of engine components however I’ve read some contradictory reports on this. I‘m looking at balancing clutch, flywheel and crank with pistons and conrods to achieve ultimate smoothness. My questions are as follows, please forgive and correct me if there are any stupidities:

 

1) Are 1.9 Gti engines balanced internally using counterweights or externally using weights on the flywheel or a harmonic damper? Or some other means?

 

2) If counterweights are used how are these weights mounted?

 

3) If a crank is lightened by knife-edging I’ve read that the weight removal causes less smoothness because the balance between crank and pistons/rods has been altered on one side of the equation only. Is this true as if so it would seem that I want just balancing, not lightening?

 

4) If the flywheel is lightened how does this affect the balancing of the engine? I’ve read that the flywheel does not affect the balance of internally balanced engines however I’m told that my flywheel needs to be balanced with the rest of the components, this leads me to believe that the Pug 1.9 Gti engine is externally balanced.

 

5) And finally (for now) what is the difference between balancing and blueprinting an engine?

 

Many thanks in advance.

[Tom Fenton 1,542]

1. The rotating parts would be balanced dynamically, by spinning and measuring imbalance at a radial position. Then a small amount of material is removed either by a drilling or grinding some off. Repeat until balanced to spec. Then bolt the assy together and rebalance as a whole.

 

2. The crank has counterweights as part of its design.

 

3. If you knife edge the crank commonly you would do more work to such as the rods, balancing then evens this out.

 

4. Not being funny but it seems you have read some s*ite, on the internet maybe? The rotating assembly is balanced, so clutch, flywheel, front pulley, crank.

 

5. Blueprinting is measuring and carefully setting all the tolerances, (gaps where things mate or slide etc).

[Rob205 1]

1. The rotating parts would be balanced dynamically, by spinning and measuring imbalance at a radial position. Then a small amount of material is removed either by a drilling or grinding some off. Repeat until balanced to spec. Then bolt the assy together and rebalance as a whole.

 

2. The crank has counterweights as part of its design.

 

3. If you knife edge the crank commonly you would do more work to such as the rods, balancing then evens this out.

 

4. Not being funny but it seems you have read some s*ite, on the internet maybe? The rotating assembly is balanced, so clutch, flywheel, front pulley, crank.

 

5. Blueprinting is measuring and carefully setting all the tolerances, (gaps where things mate or slide etc).

 

Tom, thanks for your reply. I guess from what you're saying that it is possible to lighten the crank and still achieve smoothness by taking the same amount from the pistons/rods though how simple this is remains to be seen...

[Tom Fenton 1,542]

You are trying to go far too deep into a simple subject. The crankshaft is more or less inherently balanced due to its shape. Unless an absolute idiot modifies it with gardening tools it will remain inherently balanced even after modifications. Then the dynamic balancing process will "fine tune" to the tolerance.

 

In summary, if you want to balance your bottom end components, take them to a balancing firm and let them do it.

 

If you are considering having lots of crank work done, on an otherwise standard engine, I would suggest not to bother.

[Miles 331 1 Cars]

On a std engine it's not really worth it, The factory Torrance's are fine

 

If you want some reading look here, http://www.vibrationfree.co.uk/index.html

[kyepan 291]

I used Steve at vibration free to do my crank assembly. I'll let you know how much smoother the engine is tomorrow when it gets started for the first time, hopefully.

[brumster 135 1 Cars]

Following on from the recent thread about inherent balance issues in various engine designs, I suspect you'll never get the XU to run as smooth as other modern 4 cylinder engines with balancer shafts and such.

 

I had a blue printed 1.9 8v - blueprinting is/was all the rage when you have to stick within manufacturer tolerances, often for competition use. This was a 205 Challenge engine so it had to be within manufacturer tolerances - but those allowed certain oversizing on bearings, pistons/rings, cam timing and so forth. In order to eek every last bit of power out of a standard engine, people would get them blueprinted - so someone like Skip Brown would put them to the maximum tolerances allowed within the regulations (ie. standard manufacturer measurements, oversizes allowed). Only reason I could see you bothering with blueprinting is if you have competition regulations to stay within - which you clearly don't from your post, so I wouldn't concern yourself too much with blueprinting.

 

Don't get me wrong, worth having the bottom end balanced, but don't expect the silky smoothness of a modern unit - my blueprinted lump was smooth as 1.9's go, but was a bag of nails compared to modern lumps

[petert 591]

Like any mass produced items, there are manufacturing tolerances. I've pulled apart Mi16 engines where all the pistons are within 1 gram. Others have been +/- 25 grams, or a total of 50 grams between lightest and heaviest. I always include balancing as part of a rebuild quote. For the $200, it just ensures it will run as smooth as possible, making the best possible power. It all goes out the window at the first clutch change however, when the pressure plate gets changed.

[GilesW 41]

For those looking at getting some balancing done - I too have used Steve at VF. Very good chap and doesn't just treat it 'like a job' so will listen to what and why and give you help and suggestions.

Oh - also handy as he knows looooads of people in the business if you need anything.

[Rob205 1]

Back in the mid-90's I owned a VW Golf Mk1 Gti 1800 with a completely stock rebuilt engine but with a balanced bottom end. This car was amazingly smooth and would outrun standard Peugeot 1.9 GTis both in acceleration and top end speed terms. I'm not saying it would trounce them but it would definitely pull away and there's no way that a standard 1800 Golf GTi should ever have done that so I guess that it was down to the balancing.

 

I don't know if these VW engines are inherently smooth anyway compared to the XU lump, if so then I'm never going to be able to emulate the same smoothness in my Pug.

 

I guess I'm going to try the balancing route as it's not massively expensive and with a new clutch fitted and low mileage I'm hoping never to have to change the clutch again and put it out of balance. I would be very interested in anyones experience of whether balancing alone had a noticeable effect over an unbalanced XU lump.

[Batfink 201]

balancing will not add power or make a car faster...

Edited January 4, 2012 by Batfink

[petert 591]

....but out of balance forces will reduce potential power through excessive loads on bearings etc.

[Batfink 201]

Maybe I should rephase - its not something the driver will notice or going to make the car significantly faster than its peers.

[Josh_Quant 27]

Thought you might like to see my bottom end i just bought all lighten and balanced since thats what your talking about

 

 

[Rob205 1]

Thought you might like to see my bottom end i just bought all lighten and balanced since thats what your talking about

 

 

How soon 'til you get your engine running? Would appreciate knowing if you think it's smoother than a standard engine.

[Josh_Quant 27]

Wont be this month mate probably some time next month, that a gti6 btw