Forged engine build - Importance of bottom end balance?
Discussion
I'm in the midst of building a new engine for my A3 (1.8t AGU bottom end), with rods, race bearings and all the other usual bits.
I know, among the rest of the guys on the VAG/1.8t scene, it's actually quite uncommon to have the bottom end balanced while embarking on a build like this. And, if I'm honest, I could do with out having to spend an extra 200 quid!
At the same time though, it makes sense that when spinning at 7k rpm, a few grams here and there is going to make a huge difference on the load to the bearings/crank.
Whats peoples thoughts and experiences on this? . . Any input welcome
Thanks in advance!
I know, among the rest of the guys on the VAG/1.8t scene, it's actually quite uncommon to have the bottom end balanced while embarking on a build like this. And, if I'm honest, I could do with out having to spend an extra 200 quid!
At the same time though, it makes sense that when spinning at 7k rpm, a few grams here and there is going to make a huge difference on the load to the bearings/crank.
Whats peoples thoughts and experiences on this? . . Any input welcome
Thanks in advance!
Because they're a well established engineering company and they've been doing this sort of stuff day in day out for years... They have all the best equipment and the engineers to do the job properly. If there's anyone that knows what they're doing, it's them... I'm not sure how I can be any more sure!?
I guess that's what your getting at though? . . But without getting an engineering degree and then some work experience in an engineering shop then I will never know "for sure" on that logic.......
I guess that's what your getting at though? . . But without getting an engineering degree and then some work experience in an engineering shop then I will never know "for sure" on that logic.......
Is the engine using a new crank and flywheel assembly? If so then they will never have been balanced while assembled and should be IMO, even if the components may have been balanced individually.
I wasn't working specifically on VAG engines, but when producing uprated engines we always balanced the crank/flywheel as an assembly as well as matching the weights and COGs of the con-rods.
I wasn't working specifically on VAG engines, but when producing uprated engines we always balanced the crank/flywheel as an assembly as well as matching the weights and COGs of the con-rods.
No, it's the original crank and with an OE VAG fly wheel, but from another car (G60 single mass). They're going to check the crank/journals for condition/ovality etc.
I know my rods are balance to with in a gram already and I can make sure the pistons are the same (or at least match them best I can to the rods). That's what I was thinking though, perhaps just get the flywheel, crank and pulley balanced and do what I can to match the rods/pistons up.
I know my rods are balance to with in a gram already and I can make sure the pistons are the same (or at least match them best I can to the rods). That's what I was thinking though, perhaps just get the flywheel, crank and pulley balanced and do what I can to match the rods/pistons up.
If the flywheel and crank are a new match up then yes, I'd definitely get the assembly balanced, with the pulley in place as you say. Given what you've spent elsewhere on the engine, it would be shame to scrimp on something that will affect it's smoothness, quite apart from the increased bearing loads due to an out of balance.
Many years ago the Don part of Aldon gave me some good info on balancing. He and Alan Goodwin (the Al part of Aldon) had been engineers at Rover. It was my first tuned engine build in 1986 and I was assembling an Aldon 1950 MGB kit with my 'own dun' head. I was struggling to pay for all I needed re balancing etc. He explained the cranks and flywheels (rotating masses) from 'the Factory' were good to 7000 but sort the reciprocating masses which were less well sorted usually. I took this faithfully and had balanced rods and pistons. It is probably the case modern higher revving engines are good to 8000 to have a comfort cushion, maybe someone can let us know?
Over the years we have also discovered some folk doing the balancing balance to the machine not a zero as they have machine faults and this can worsen the balance. I have even seen bent cranks balanced! make sure the crank is checked for trueness first!
If you have a flywheel which has been balanced at some time with obvious drillings, be careful, many folk balance against a worn ring gear instead of replacing ring gear then checking balance. This usually shows as loads of drillings opposite the worn teeth!!!!
Balance of rods is important as quite often damaged rods have been replaced not in sets during engine rebuilds in the past. Some brands of pistons are better than others.
I guess I am saying reality and experience are not the same as theory.
Peter
Over the years we have also discovered some folk doing the balancing balance to the machine not a zero as they have machine faults and this can worsen the balance. I have even seen bent cranks balanced! make sure the crank is checked for trueness first!
If you have a flywheel which has been balanced at some time with obvious drillings, be careful, many folk balance against a worn ring gear instead of replacing ring gear then checking balance. This usually shows as loads of drillings opposite the worn teeth!!!!
Balance of rods is important as quite often damaged rods have been replaced not in sets during engine rebuilds in the past. Some brands of pistons are better than others.
I guess I am saying reality and experience are not the same as theory.
Peter
Save your money. You won't notice a scrap of difference getting a stock crank balanced. It'll already have been balanced on equipment a damn sight more sophisticated than most engine tuners have. Same with a stock flywheel or clutch. 5 quid for a set of 1g x 10kg digital scales off Ebay and do the rods and pistons yourself to 1 gram. Job jobbed.
Edited by Pumaracing on Wednesday 18th February 07:52
Pretty much every possible opinion there... ha ha! The last one suites my budget, thats for sure ;-)
The other side of the coin is that the flywheel and clutch assembly are already in the car on the engine that is being replaced... I was kind of hoping to do the engine swap in one weekend but if I were to balance the clutch/fly/crank/pulley together then I'd have to rip the old engine out just to finish building the new one!
Not what I was planning on :-/
Pumaracing, have you got much engine building experience? . . As I said I know very few of the 1.8t boys bother with balancing on builds like this. And I'm starting to lean that way my self if I'm honest! Save me the time money and hassle, that's for sure!
The other side of the coin is that the flywheel and clutch assembly are already in the car on the engine that is being replaced... I was kind of hoping to do the engine swap in one weekend but if I were to balance the clutch/fly/crank/pulley together then I'd have to rip the old engine out just to finish building the new one!
Not what I was planning on :-/
Pumaracing, have you got much engine building experience? . . As I said I know very few of the 1.8t boys bother with balancing on builds like this. And I'm starting to lean that way my self if I'm honest! Save me the time money and hassle, that's for sure!
VAGslag said:
Pumaracing, have you got much engine building experience?
I have heard a rumour he knows which end to bolt the flywheel on 
For some reason his website is down or been changed. But that would answer your questions. So let's just say that he has probably forgotten more than most people will ever know
In my experience factory balancing is adequate, what usually queers the pitch is fitment of aftermarket lightweight flywheels and replacement clutches, these are rarely well balanced and they have a large rotating moment, their fit to the crank or flyhweel is often slighty eccentric and there may be a degree of latency in the fit. If you are replacing the clutch then it is worth having it balanced on the flywheel being used even if it mounted in a drone crank to undertake it. Make sure it's index position is marked and that it is balanced and assembled at the same rotational point (usually TDC 1/4).
Dsve
Dsve
Edited by DVandrews on Thursday 19th February 22:20
Archive of my old web site here as always.
https://web.archive.org/web/20110902010921/http://...
Scrolling down to the article on flywheel balancing might be informative as regards this thread.
https://web.archive.org/web/20110902010921/http://...
Scrolling down to the article on flywheel balancing might be informative as regards this thread.
My recent Pinto build had the rods & Pistons balanced as Puma did with kitchen scales
The other engine that has a light steel flywheel and uprated clutch cover had the rods and Pistons done on the scales before and engine balance was done, there was quite a difference as the light flywheel and clutch cover were out by an unacceptable margin.
It's a hobby for me that I enjoy doing and also learning about
The other engine that has a light steel flywheel and uprated clutch cover had the rods and Pistons done on the scales before and engine balance was done, there was quite a difference as the light flywheel and clutch cover were out by an unacceptable margin.
It's a hobby for me that I enjoy doing and also learning about
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