_Bomber Watson_
Posted 21 June 2013 - 06:59 PM
Would it be worth the effort to cut and shunt a couple of blue motor cranks?
Use the end journals/counterweights off two cranks, with the biggest counterweights centered....Still wold be to light probably but would assume it would be better?
I have one here with a #@$^%& rear main that could be used for the middle two throws.....
Cheers.
Lotsa Posts!
Posted 22 June 2013 - 08:56 AM
Might be a bit of a task to try and graft a couple of peices crank together,getting them phased
properly would be hard enough let alone trying to get them to stay together to put up with the
punishment it will receive.
Had a thought about drilling the big end pins and using some mallory slugs on the weights but man that stuff is
fairly expensive but I have managed to find someone who can supply 4 feet of the stuff that is just under 1/2 inch
diamater,and at the right price.
Was thinking of spreading the slugs evenly over the circumferance of the counter weight to try and keep some
of the moments of mass where they should be rather than just put them at one point.
Spoke to a bloke who drilled out the pins on a blue six crank and he got 200 grams of metal total which
works out to about 33 grams from each pin,although he did break into one gallery this was because the jig
to guide the drill was not set up properly.
Oh joy,,should one even bother.
_oldjohnno_
Posted 22 June 2013 - 09:21 AM
Might be a bit of a task to try and graft a couple of peices crank together,getting them phased
properly would be hard enough let alone trying to get them to stay together to put up with the
punishment it will receive.
Had a thought about drilling the big end pins and using some mallory slugs on the weights but man that stuff is
fairly expensive but I have managed to find someone who can supply 4 feet of the stuff that is just under 1/2 inch
diamater,and at the right price.
Was thinking of spreading the slugs evenly over the circumferance of the counter weight to try and keep some
of the moments of mass where they should be rather than just put them at one point.
Spoke to a bloke who drilled out the pins on a blue six crank and he got 200 grams of metal total which
works out to about 33 grams from each pin,although he did break into one gallery this was because the jig
to guide the drill was not set up properly.
Oh joy,,should one even bother.
Forget about the Frankenstein crank, there's no way you'll do that with a cast crank and have it stay in one piece.
You could possibly pull some weight out of the crankpins, but again remember it's a cast piece and it'd be easy to create weak areas.
If you go the heavy metal slug route, you don't have the luxury of deciding where to put them - you'd want to replace as much of the counterweight as you can with Mallory, wherever you can without making it rip apart from all the perforations.
You keep talking about crank mods, I keep bringing up lighter pistons and rods. I honestly think you are attacking this from the wrong end. It's going to be expensive to mod the crank, and it'll be weaker when it's done. I'm sure you can get some weight from the rod, pins and pistons - and remember this is where the shakes are coming from in the first place. It doesn't matter what you do with the "balance" factor, to reduce the shakes you need to reduce the mass of those bits creating them.
Lotsa Posts!
Posted 22 June 2013 - 09:33 AM
I will give the rods and pistons some thought as well to see what can be done,the pistons are currently 60 over and are
actually lighter than the stockers,might give the red rod some consideration as they are much lighter than blue rods by quite
a margin,will have to see how much meat can be shaved off these items as well.
_oldjohnno_
Posted 22 June 2013 - 09:39 AM
Don't forget the pin; a shorter, taper wall pin would help. And you can usually take a lot of weight from the rod cap.
_barana_
Posted 22 June 2013 - 12:32 PM
so what are the lightest 202 pistons available? and the lightest 202 rods available? if we have a weight benchmark, i could see if i could beat it with carbon pistons. the brock 75 rally gemini 2.2l used a prototype starfire which had really bad shakes at certain rev ranges, would this be because it had bigger pistons than the 173 pistons, or because its possible they used a 3 phase crank from a 6 cut down so only two phases were left ...wonky.
now that the starfire crank is okish in the production items we could just stroke it out to a 2.2l ? (is the production s.f. crank 1 2 or 3 phase?)
it has centre counterweights like a redmotor, could we benefit by bombers idea of cutting and shutting the _large_ blue202 counterweights on all the crank throws, to male it a fully counterweighted crank ? Thereby keeping it well 'balanced' so to speak even at the prospect of capacity increase?
_barana_
Posted 22 June 2013 - 12:36 PM
and get this cut and shut model made out of billet once it has been confirmed balanced as much as a four....
IDK, sounds like a lot of bullshit just to get small gains, would be easier to build a toothed belt and some sheetmetal boxen off the sides to run some balance shafts......
_barana_
Posted 22 June 2013 - 02:04 PM
run an ohc head, use a harmonic based crank angle sensor ah la 3.8 v6, along with the delco emu, use the now redundant camshaft gallery as a balancer shaft gallery and only have to add a second balancer shaft sheet metal gallery under the exaust manifold....
_barana_
Posted 22 June 2013 - 02:37 PM
sorry oldjonno, i should delete all that.
I understand that to stop the vibrations, I need to reduce the piston and rod weight, and increase rod length, as much as i can.
Edited by barana, 22 June 2013 - 02:39 PM.
_barana_
Posted 22 June 2013 - 02:55 PM
re the bs, I didnt mean chucking out the ideas of lightening pistons and rods.
_oldjohnno_
Posted 22 June 2013 - 04:27 PM
sorry oldjonno, i should delete all that.
I understand that to stop the vibrations, I need to reduce the piston and rod weight, and increase rod length, as much as i can.
It's all good mate 
Lotsa Posts!
Posted 23 June 2013 - 08:52 AM
Dont see any point trying to cut and shut cranks,pretty well stuck with what we have,the s/fire crank is
what is supposed to be fully counteralanced but as can be seen the big end pin is too heavy for the balance.
Like oldjohnno says,get the reciprocating bits as light as possible to try and get the counter weight more effective,however
the calculated weight that the counter balance needs to be using current parts is 808grams and even though lighter pistons,rods and pins will
help just looking at the the thing it will need some weight off the pin and probably some added to the counter weights.
The lighter rods etc is the easy part,making a jig to do the drilling is the tricky bit as well as getting it true before drilling,but gravity is our
freind along with some simple tools.It may not be worth the effort to some in the long run,but shit,if you dont try you dont know.
It will either be 10 times worse or 10 times better,at least it will give a indication of where to go or not to go.
If it does help I will be happy,according to some helpfull people I spoke to if the balance is not right it will not rev out,this may be true or not,i dont know.
This seems to be what is wrong,those little shits of things should rev out to 6 and probably beyond easily but they dont,the best I got
was just over 6 but it seemed like a struggle to get there.See what happens i guess.
I dont mind spending a bit of time making stuff to do the job but not willing to spend awsome quantities of cash just on what basically
is more or less a bit of backyard development to find out why the horrible little things are like they are.
_oldjohnno_
Posted 23 June 2013 - 10:07 AM
Like oldjohnno says,get the reciprocating bits as light as possible to try and get the counter weight more effective,however
the calculated weight that the counter balance needs to be using current parts is 808grams and even though lighter pistons,rods and pins will
help just looking at the the thing it will need some weight off the pin and probably some added to the counter weights.
You're missing the point altogether.
Let's say the current balance factor is 20% (probably a pretty close guess). Run the engine at 6000 with a vibration sensor attached and record the reading.
Now strip it down and stuff the counterweights with heavy metal until you get the theoretically optimum 50% balance factor. Put it back together and again run it at 6000 with the vibration sensor. Even though it is now "fully balanced" the reading will be the same. All that has changed is that you've made life easier for the mains.
The bottom line is this: if you want to reduce the shaking you have to reduce the mass of the reciprocating bits. More counterweight will help the mains but if they are coping OK now (and I expect they would with a 3" stroke and only 6000rpm) then I'd class the crank work as being nice to have but not the priority. If you're only going to be turning 6500 or so with a 3" stroke and a light piston and pin I'd definitely go with red rods. Pull some weight out of it and you'll probably find the crank is acceptable as is.
_barana_
Posted 23 June 2013 - 08:41 PM
@ oldjohnno would you still go red rods with 3.25" stroke, 6500 lightweight 202 piston and lw pin ?
@noballsuc
but shit,if you dont try you dont know.
It will either be 10 times worse or 10 times better,at least it will give a indication of where to go or not to go.
If it does help I will be happy
yeah me too me tips me hat to ur pioneering spirit, and thankyee for the experience ya bring to the table, even if it doesnt work.
_But_ if it does.... :>
Edited by barana, 23 June 2013 - 08:47 PM.
_oldjohnno_
Posted 23 June 2013 - 09:25 PM
@ oldjohnno would you still go red rods with 3.25" stroke, 6500 lightweight 202 piston and lw pin ?
No, I think you'd really be pushing your luck; the factory wouldn't have upgraded the rods for no reason.
_barana_
Posted 23 June 2013 - 10:18 PM
ok another question,
6500rpm, lw 202 pistons lw rods lw pins 3.25" stroke factory crank at guestimated 20% balance factor..... do the mains have a problem now?
If I change out the lw 202 pistons for carbon jobbies would that change your above answer?
_oldjohnno_
Posted 24 June 2013 - 07:53 AM
ok another question,
6500rpm, lw 202 pistons lw rods lw pins 3.25" stroke factory crank at guestimated 20% balance factor..... do the mains have a problem now?
If I change out the lw 202 pistons for carbon jobbies would that change your above answer?
I don't know, except to say that the answer would be "it depends".
Is the engine a drag racer that only runs 10 seconds at a time? Or an endurance boat engine? For short duration work I'd be happy to run light components to 6500 with little or no counterweighting but to not much more than 6500.
And if it's a Holden six we're talking about, then it's a special case. These blocks are nice and light, but not very rigid. If you look at the typical failure patterns at high rpm you find that the actual bearings generally survive quite nicely (given an uninterupted oil supply) but the block itself shows signs of being jerked around. Longitudinal cracking, outright breakage, welch plugs rattled out etc. So yeah, if it's going to be turning a few rpms I'd definitely try to get some counterweight happening. But this is only part of the picture, there's reason to believe that the block itself tends to resonate, and that this may be set up by torsional vibration which is a whole other story. So crank balance is just part of the picture.
If you look at the bottom end of the block, it looks like it would be stiffer vertically than it is horizontally. I have no proof of this but thats what it looks like. Given this, I'd probably want to have some amount of underbalance, where a small decrease in lateral forces are swapped for slightly higher vertical forces. This is what you'll get anyway with a stock 12 port crank. These look a bit odd but I think the factory engineers knew what they were doing and the result was a crank with good running characteristics that wasn't too heavy. Lots of people have had good results using these at high rpms with the counterweights reduced slightly, and that would reinforce the theory that a fair bit of underbalance is a good thing with these blocks at high speeds.
The other thing to consider is where the counterweights are located. The ideal place (as far as making life easy for the crank and block is concerned) is as close to the cylinder centreline as possible. See the photos that Ned posted in the other crank thread, and see how the weights are contoured. This is the ideal. At the other end of the scale is the Starfire crank. Because each throw only has a counterweight on one side the crank and block is always going to be subjected to some bending forces no matter what balance factor you use. Probably not so bad with the shorter, stiffer block but again I'd compromise with a fair amount of underbalance.
Lotsa Posts!
Posted 24 June 2013 - 08:36 AM
Fair enough oldjohnno,I do tend to miss things sometimes.
The mains on the previous engine did not seem be coping very well at all,unfortunatly they are at someone elses place (like a dickhead I discarded them into his collection).
Although that engine had done quite some miles from memory they were fairly worn on the horizontal plane,the end ones seemed the worst but the middles had the same pattern although I think not quite as bad,I did not look real hard as i should have but I remember the bloke helping me strip it remarking that it was an "odd" wear pattern and over the last 30 years He has seen inside a few engines so all I could really do was take his word that it was odd and start looking.
_barana_
Posted 27 June 2013 - 10:50 PM
Re adding balance shafts to the starfire if increasing capacity.......
this is how they did it on the 2.5l ecotech from the malibu........
note the cradle and the balance shafts that bolt upto the bottom of the block cradle.
Lotsa Posts!
Posted 29 June 2013 - 08:46 AM
I not to sure about adding balance shafts,from what can be found adding balance shafts is something usually
done to engines with a cylinder size of over 500cc.
Another thing about adding balance shafts is that it will be an engineering nightmare that I feel is probably not
warranted in this case.Not only that,adding balance shafts does not really address the fundamental problem with
the starfire,if a relatively simple modification can help then I think that it is easier to start with the simple things and go from there.
Something else about balance shafts if the info. is correct is that they dont really fix a problem,they are more or less to take out
"residual" shakes so that it makes a silky smooth ride for the occupants of the car.
What I have in mind may or may not help,it might not fix it perfectly but as already stated there is no such thing as a perfectly balanced
engine,,any improvement will be good.Who knows,if its better it wont be getting any kind treatment from me.
_doucmyuc_
Posted 29 June 2013 - 10:00 AM
Why are you wasting time thinking about balance shafts?
Balance the rods and pistons and pins, get some high quality machine work done, coat the piston skirts and hand prepared your piston rings. This will reduce the majority of your problems.
_STRAIGHTLINEMICK_
Posted 29 June 2013 - 12:43 PM
I think there isnt much you can do to fix the vibration besides balancer and flywheel tuning , I would just keep it simple and if you keep weight in parts that rotate and reduce weight in parts that go up and down then it will be as good as it can be . Although if the head flows well i would be looking at a long rod stroker for it .
_oldjohnno_
Posted 29 June 2013 - 02:00 PM
I think there isnt much you can do to fix the vibration besides balancer and flywheel tuning , I would just keep it simple and if you keep weight in parts that rotate and reduce weight in parts that go up and down then it will be as good as it can be . Although if the head flows well i would be looking at a long rod stroker for it .
I agree that there's not much you can do about torsional vibration apart from the flywheel and balancer. But I'd bet every dollar I have - yep, both of em - that in this case the problem is just a plain old secondary imbalance and could be markedly improved by pulling some reciprocating weight out.
Lotsa Posts!
Posted 01 July 2013 - 09:49 AM
Just a recap on what has been tried.
Have tried different flywheels,no difference.
These things did not have a harmonic balancer to start with so one was fitted,no difference.
Pistons/rods etc were balanced out,the +60 piston is lighter than stock,cant remember by how much but it was probably by the
ammount that the steel that was around the pin boss area that was in the stock piston.
I am still not 100% convinced that flywheel and balancer changes will help simply because there are a couple of
202's around here in stockies with quatermaster clutches hanging off the end of the crank with no more than a ring gear from
an auto for a flywheel and to start the thing with a starter.They dont seem to have any drama at all being flogged around
a track at over 6k for half a day.
There is one that was running an alloy flywheel until number one throw sheared clean off at the
main journal.This was thought to have been caused after dry sumping the thing because it used get a strange "singing" sound at high
revs.and resonance was being blamed,it also used to vibrate real bad at those revs.
A stock flywheel was fitted and same thing resulted,turns out beleive it or not it was the tailshaft that was at fault.
These cars were running romac balancers.
Ok, so a starfire is not a six and a starfire has bad shakes,when i say bad I mean not normal,not even a datsun 1900 shakes like
these things,even the opel or ford 1900 was much better.
It is hard to describe,it is sort of like it affects your ears as well as shaking shit off,it is not normal at all.
I have had bit of look at primary and secondary balance but still getting head around it.
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