Randy's post on crank counterweight and balance shafts

[DDtB]

That has to be one of the rudest (mis)uses of a community forum I've ever seen.

An introduction or even a 'hello' first might have been nice... but simply re-posting a comment here and then linking to it from another forum just because they locked the original thread over there is a bit pathetic really.

[steve_weegie]

KingK / Simon,

Sorry, I'm unaware of the history on this thread. Is this a Honda K20A that you're turbocharging, complete with block girdle for torsional rigidity? I've heard of people adopting this approach on the Duratec block, but not a Honda.

Have you retained the VTEC with some timing tweeks for the turbo?

Cheers,

Steve

[mckeann]

am i the only one to think this is all a bit random?

It is an attempt to continue a perfectly civil and I hope useful conversation that got stymied elsewhere - in part for being unable to post pics

This isn't a proxy forum - if you are interested in contributing to the Scottish Elise scene, then you're welcome here, if it's just to use the forum as a picture resource, please don't let the door hit you on the way out.

If you think this is going to be a suitable site to continue one of your infamous 'debates', you'll be disappointed.

ahem: http://forums.lotrdc.com/viewthread.php?tid=1193


seems like SE is only good for when you get kicked off other forums.

[KingK_series]

KingK / Simon,

Sorry, I'm unaware of the history on this thread. Is this a Honda K20A that you're turbocharging, complete with block girdle for torsional rigidity? I've heard of people adopting this approach on the Duratec block, but not a Honda.

Have you retained the VTEC with some timing tweeks for the turbo?

Cheers,

Steve

Hi Steve

No It was Chris Randall's Europa turbo project, - he ran it in Lot and I believe doing the GT cup next year. We were having a discussion about the merits of an OE engine vs a tuned one, and I was drawn into discussing Sean Bicknell's 2007 Lot engine that I built, it wasn't the serious part of the discussion, but I wrote a bit about what happened with Sean and the engine when it broke at Spa - Sean has never "added" to the post he put up on Exiges, despite having heard Arrows verdict and been sent pics of the internals. Clearly the forum host is looking after his clients, but it was a shame because there was a much more interesting discussion about ecu's, mapping and Randy's work on his Vauxhall short end that might have been useful to others. Anyway there was a perfectly civil discussion, no one was upset on the thread, so I thought I might continue it elsewhere, just in case it was useful to Randy or of use to anyone else.


No I am not tuning a honda, my only interest is in opening people's eyes to the K by demonstrating how successful it can be if done right, but I do own several hondas now that have blown in Elises - both K20As and K20Z4s, and the useful discussion I had hoped was to illustrate how crank design is affected by the use of balance shafts. This was relevant to Randy's Europa project because he removed the balancer shafts [ saving weight] but there was then the issue of block rigidity - and he has been spending time abd effort on a billet ally sump to stiffen the engine up. Since I have had these hondas, I have been able to measure them for dynamic unbalance - to compare to stock Rover Ks and I will at some stage find some Audi's and Duratecs, but also assess them for counterweighting.

This was very interesting issue to me when I embarked upon my own crank design 10 years ago, and hence initiating the K series single piston tests which unfortunately have become somewhat subverted and the issues clouded. Discussing Randy's Vauxhall seemed like a good way of restructuring the discussion as well as contributing to Randy's project if he had not done this work already.

Anyway I hope the TECHNICAL issues are of interest to someone....?

[KingK_series]

[quote seems like SE is only good for when you get kicked off other forums.[/quote]


I can still post there, and the thread was going really well, only person upset was the moderator because I wrote a bit about the spa engine failure...

If Randy reads the Lot link and come sover here, maybe there will be useful discussion, otherwise the thread will die..... no matter

[Randy]

Have to be brief as I'm up to my ears in a race prep for tomorrow...

Have a read here... http://www.hofmanns.co.uk/content/index.asp?id=74 we did some testing of the crank and found it under counterbalanced but didn't have the time/money/rpm's to heavy metal it at the time so it's run all year in largely sock form and without problem. I'll be looking at the bearings before the start of the year to see if they are wearing evenly but luckily the block is very stiff so that will help hold the crank straight.

[KingK_series]

Have to be brief as I'm up to my ears in a race prep for tomorrow...

Have a read here... http://www.hofmanns.co.uk/content/index.asp?id=74 we did some testing of the crank and found it under counterbalanced but didn't have the time/money/rpm's to heavy metal it at the time so it's run all year in largely sock form and without problem. I'll be looking at the bearings before the start of the year to see if they are wearing evenly but luckily the block is very stiff so that will help hold the crank straight.

Ok I see you looked at it, and 300g deficit x 8 = 2.4kg when you are using a much lighter piston. Compare that to the 2 K20 crank varieties and there is a weight difference of 3kg with the same piston rod. Honda were able to do that because the balancer shafts not only help against the secondaries, but act against the primary axial inertia forces. So Lighter crank produces a smoother engine with the shafts.

Given your deficit on the Vauxhall, I'd be inclined to bet their designers knew exactly what they were doing with the shafts to reduce the necessary counterweight, - ie the shafts are not there for "just NVH". In my experience you need to run an engine for a very long time before you see significant main bearing wear. It may interest you to know that the HMI K series cranks are now just 0.8kg heavier than stock, - 1.2kg less than the chief advocate for HMI K series crank's on seloc. Not going to get drawn into why for any money, but that still does not allow for the benefit you get from fluid forces acting on the crank against axial inertia forces, so a really "ideal" K series crank would weigh less still - going to keep the numbers for my book, but compare the numbers and you can reasonably assume that Rover K in stock form is very close to ideal whereas a honda Z4 crank or Vauxhall crank [even with much lighter pistons] is a country mile off from ideal or the loading that the Rover sees, when the balancer shafts are removed. Given then that the block is very stiff, but the caps even in iron are never going to approximate to a single crank carrier arrangement like K or K20 and there is probably considerable scope to improve matters. This is certainly the area where the block is going to be most tested rather than at the deck.

good luck with your race tomorrow

[Edin430]

[Randy]

I have no doubt that the Vauxhall crank has it's deficiencies and that GM weren't be complete mugs when they strapped balancer shaft to it... However... it bothers me little as the engine, in it's current form, already makes more power than I'm allowed run next year so I can wind it down and get even more reliable. Also, there will be a relatively high weight limit for me next year too so the absolute weight of the engine will be largely irrelevant and the handling effects placated by the addition of large lumps of lead up the front of the car. There is no point whatsoever in me wasting any of my precious (in that I have little of it) resource on redesigning a crank that has been cheap, reliable and hit all my performance targets over the last year. In fact I have no intention of changing anything on my engine which is great news as it means all my resource can go into the bit I enjoy more and that always yields good performance improvements with zero reliability problems and that is making it go around corners faster.

What confuses me is how the Rover K-series setup is so great when every one I've taken apart (which admittedly not that many) has a crank in either two halfs or fcuk bearings. To my eyes the K seems to have a block made of cheese and allows the cranks to flex... Otherwise how do you explain the uneven wear on the bearings?

[steve_weegie]

Randy, can I ask what prompted you to remove the balancer shafts? I spend a fair bit of time mapping the Saab B204/234 engines these days, and there's certainly mixed opinion regarding shaft removal when increasing the rev limit into the 7000+ range.

Dont think there's any doubt that the use of balancer shafts will affect an optimal crank design & weight, but I guess you need to weigh up the benefits of having a very well balanced engine, complete with balancer shafts spinning at huge rpm, or 2nd order vibrations and their associated induced crank & block stress... Probably different criteria for race and road cars, but an interesting topic none the less... What is more likely to fail - a balancer shaft spinning at 4000rpm above its design, or a crank, block and bearing assembly thats subjected to stresses it wasn't designed for?

Who knows There's probably no correct answer

[Randy]

The GM engine block in the Europa has been used in many million GM cars since the 70's (search 'GM family II' engine). The addition of balancer shafts on the Z20LET/Z20LER version of the engine is a recent one and there to help with NVH. All I have done is change the Z20LER (Europa fitment) setup to a Z20LEH (Astra VXR) fitment which has no balancer shafts as standard. As discussed on other threads, the only non-stock parts of my engine are the Arrow rods.

[KingK_series]

Randy, can I ask what prompted you to remove the balancer shafts? I spend a fair bit of time mapping the Saab B204/234 engines these days, and there's certainly mixed opinion regarding shaft removal when increasing the rev limit into the 7000+ range.

Dont think there's any doubt that the use of balancer shafts will affect an optimal crank design & weight, but I guess you need to weigh up the benefits of having a very well balanced engine, complete with balancer shafts spinning at huge rpm, or 2nd order vibrations and their associated induced crank & block stress... Probably different criteria for race and road cars, but an interesting topic none the less... What is more likely to fail - a balancer shaft spinning at 4000rpm above its design, or a crank, block and bearing assembly thats subjected to stresses it wasn't designed for?

Who knows There's probably no correct answer

I agree entirely, unless you substantially lighten the pistons and then modify the crank to suit.

My King K fully bridge pistons weigh 234gmm, all up ie piston, pin and rings

OE K seris pistons wight 296gmm - designed especially so for low secondaries and therefore for no balance shafts and a light crank

OE honda 437gmm! - hence honda redesigning the K20 with balance shafts

OE GM ?

[Gourlay83]

Jeepers, its his engine. He can do what he likes.

Randy, is it you who sells the small Honda Gators ?

Alan

[Randy]

It's all very well quoting piston weights but the K20 Honda's are as bullet proof as you're ever going to get and my experience of the GM engine is that it's superb as well so they must be doing something right. Rover K pistons are fragile, so are the cranks, so are the blocks, so are the heads etc etc etc...

[Randy]

Jeepers, its his engine. He can do what he likes.

Randy, is it you who sells the small Honda Gators ?

Alan

Yes... that's me, the one who has found out, through bitter experience, how to get Honda driveshafts to hold together in race use!