_Bomber Watson_
Posted 17 November 2013 - 01:52 PM
Edited by Bomber Watson, 17 November 2013 - 01:53 PM.
_oldjohnno_
Posted 17 November 2013 - 02:30 PM
The loosening of the bolts isn't the problem; it's just a symptom of the real problem. Solutions like lock-wiring and loctiting are band-aids at best, the only way to keep the bolts tight is to eliminate all possible movement between flywheel and crank. If you can do this then life will be easy.
Providing the faces and spigot are in good shape then all you need is two tight (keyword: tight) dowels. The holes have to be reamed nice and round and straight and it should take some effort to drive the dowels in. If they aren't tight enough or well fitted they simply won't work. The 3/8" bolts are fine but people use 7/16" without problems too. Whether you use factory or ARP bolts be sure to bed the heads in as per ARP's instructions - this is important. The ARP bolts will take a lot more torque than the factory setting and I'd guess that the factory ones would take a bit more too. People will tell you that the small heads of the ARP bolts will cause the world to end but this is horseshit - provided the heads are bedded in properly they're fine.
You can get most of the benefits of the relief groove simply by countersinking the holes in the flywheel and crank. I also clean the faces and apply a light film of loctite to them but have no idea whether this actually achieves anything.
One last thing: you need to maintain a relationship between the weight of the flywheel and that of the balancer. In other words run a light balancer with a light flywheel, a heavy balancer with a heavy flywheel. The worst combination as far as shaking flywheels and clutches off is a heavy balancer and a light flywheel.
Edited by oldjohnno, 17 November 2013 - 02:32 PM.
_Agent 34_
Posted 17 November 2013 - 03:55 PM
just to add to this tread, mine came loose last weekend with 800 mile on the fresh engine.
We are yet to pull the box out and have a good look , but the flywheel is walking off the crank. Yep it was after a big rev into the 6- 6.5k range and it happened on the back rev or this is where i heard the first noise.
So just to let you know about my set up , it's a full weight crank , with a power bond up front and some " minor " weight taken off the standard fly wheel. It had two dowels.
maybe the next step is to go to a romac up front, but I'm unsure taking this approach, unless it's fully though through.
G
_Bomber Watson_
Posted 17 November 2013 - 04:00 PM
Back to the torsional thing, Imagine the forces, the flywheel has most of its weight on the outside, and its happilly spinning at 6500rpm, then you come off the throttle and suddenly the crank is trying to slow it down, the flywheel wants no part of this and due to Newton's law wishes to keep ding what its doing.
Just prior to this the crank was trying to accelerate the weight around the outside of the flywheel, so any slack which may have been there (probably slack is the wrong term but i'll use it) was taken up in one direction, button off, suddenly theres all this weight in the opposite direction, flywheel slips a micron....Then it all goes shit shaped.
Thats my theory anyway, similar to holding some revs up its ass and buttoning off the clutch, same kinda rapid force change.
Cheers.
_oldjohnno_
Posted 17 November 2013 - 04:46 PM
Back to the torsional thing, Imagine the forces, the flywheel has most of its weight on the outside, and its happilly spinning at 6500rpm, then you come off the throttle and suddenly the crank is trying to slow it down, the flywheel wants no part of this and due to Newton's law wishes to keep ding what its doing.
Just prior to this the crank was trying to accelerate the weight around the outside of the flywheel, so any slack which may have been there (probably slack is the wrong term but i'll use it) was taken up in one direction, button off, suddenly theres all this weight in the opposite direction, flywheel slips a micron....Then it all goes shit shaped.
I know what you're saying but the inertial forces are miniscule compared to the hammer blows of vibration. Things often turn to shit during a shift (especially a missed shift) when the damping effect of the load is disconnected and the revs are high.
just to add to this tread, mine came loose last weekend with 800 mile on the fresh engine.
We are yet to pull the box out and have a good look , but the flywheel is walking off the crank. Yep it was after a big rev into the 6- 6.5k range and it happened on the back rev or this is where i heard the first noise.
So just to let you know about my set up , it's a full weight crank , with a power bond up front and some " minor " weight taken off the standard fly wheel. It had two dowels.
For the bolts to become loose so quickly I'd have to suspect the dowels weren't well fitted and/or some other problem with fitment.
_Dansthemanow_
Posted 17 November 2013 - 06:50 PM
its on overun when the load is off the engine that I hear the sound of the loose flywheel vibrating.its basically slipping back and forth at high frequency on the end of the crank.It seems that when the engine is a high revs,but unloaded, thats when the TV really kicks in.The end of the crank is oscillating clockwise,then counterclockwise, and obviously the weight of the flywheel means it cant speed up and slow down at high frequency like the crank and this results in the fly slipping back and forth untill the bolts work loose,or even if the bolts cant unwind due to lockwiring, eventually wear takes place at the mating faces which reduces the tension of the bolts.If you only have bolts,then it is purely friction between the mating surfaces preventing the flywheel spinning off the back of the crank.Bolts do not locate mating surfaces,they only give a clamping force,friction does the rest.Basically you need either dowells to locate the flywheel,or increase the clamping load provided by the bolts so that there is enough friction between the two surfaces to prevent this slipping back and forth.
Back to the dampening factor,I originally had a large alloy custom balancer on the front in conjunction with the alloy flywheel ive still got.It seemed to last a fair time before the first time it came loose.Then I changed that balancer due to some degradation of the rubber in the balancer.Maybe that balancer was doing a good job untill the rubber let go.Although it was overall similar weight to a stocker,being wider than standard and made from all alloy,perhaps it was damping better at high rpms. I could get that balancer rebuilt.The power bond race balancer hasnt eliminated the problem.From what agent 34 said,even a heavier flywheel may not eliminate the problem.Maybe a heavy romac in conjuntion with a heavy flywheel might work.
I wander what the guys racing them in muscle car and group nc do about it.Perhaps the stocker balancers and even the powerbond are all wrong,as that style balancer was designed for very low rpm.The power bond look largely identical to standard.I mean the rubber is perhaps a bit different.Perhaps something more exotic is in order.
_Dansthemanow_
Posted 17 November 2013 - 06:58 PM
I wander if what kind of bolt torques people have used with the standard size bolts.I think factory setting is 50 or 55 ft/lbs.How high can you go without damaging the thread in the crank?
_oldjohnno_
Posted 17 November 2013 - 07:25 PM
65 lb ft is no problem at all. This is one of those areas where everything absolutely positively has to be right - the faces must be perfect and the dowels have to be tight in both crank and wheel, and you have to fit the bolts using the proper procedure. If it isn't 100% it simply won't work.
You can't just drill some dowel holes and torque up the bolts and expect it to work, though it seems that this is what sometimes happens. If you can get the flywheel off again with nothing more than a couple of small pry-bars it's too loose - it should really take some effort.
Edit: if the bolts have come loose on a flywheel with dowels you'll almost certainly have to ream the holes for oversize dowels - the holes will be out of round (and it's likely they were too loose to start with).
Edited by oldjohnno, 17 November 2013 - 07:28 PM.
_Gunmetal LH_
Posted 17 November 2013 - 07:25 PM
_oldjohnno_
Posted 17 November 2013 - 07:30 PM
These little buggers would work pretty good I reckon? They tighten up as normal washers but when you go to undo them they actually get tighter.
You're missing the point - the problem isn't the bolts loosening, it's the flywheel moving on the crank. Fix this and the bolts will stay put.
Oh My, Don't you post alot
Posted 17 November 2013 - 07:55 PM
I continue to be amazed at how much you guys know...!!
_Gunmetal LH_
Posted 17 November 2013 - 08:07 PM
To oldjohnno- Right, got it now. I was thinking of it the other way around and blaming (partially) the bolts.
_202DOHC_
Posted 18 November 2013 - 12:10 AM
For your interest,
A 3/8 UNF grade 8 bolt tensioned to 50ft/lb has 7900lb clamping load with 6 3/8 UNF bolts holding the flywheel on you would have 47400lb of clamping pressure.
See attached web site.
http://www.spaenaur....ectionD/D48.pdf
Oldjohnno is correct red crankshafts at around 3000 and 6000 rpm do develop harmonics, you need to stay out off these rev ranges because it will loosen flywheels and outer rings on standard harmonic balancers.
_oldjohnno_
Posted 18 November 2013 - 06:52 AM
Something else to consider: if you're going to fit dowels and cut a relief groove I'd make the groove no more than say .003" deep. If you can picture the two mating faces in cross-section the groove will put some distance between the faces right where the dowels pass through. Obviously this isn't ideal as far as maintaining the highest possible shear strength of the dowelled joint. I'd either skip the groove and just countersink the holes or else make the groove as shallow as possible.
_Dansthemanow_
Posted 18 November 2013 - 09:09 AM
_oldjohnno_
Posted 18 November 2013 - 09:53 AM
I think with dowels you wouldnt bother with the groove
Without the groove you need a fairly big but shallow countersink around each crank hole. And as Wayne mentioned the real root cause is the torsional vibration - TV>flywheel movement>loose bolts. So playing games with the bolts is attacking the problem from exactly the wrong end. Heavy balancers tend to transfer more vibration to the back, so you definitely don't want to go any heavier than necessary on the front, especially with a light flywheel. I'm sure the TV problem can be overcome, but it'll take some testing.
_Dansthemanow_
Posted 18 November 2013 - 12:41 PM
_Agent 34_
Posted 18 November 2013 - 06:19 PM
These little buggers would work pretty good I reckon? They tighten up as normal washers but when you go to undo them they actually get tighter.
i saw these washers at the engine guys today and far out they grab, this was one fix.
i think that we are going to do this;
the guys have said that lock plates have worked for them in the past, but other things like , bigger bolts, etc have not.
i'll post photos of the work.
_Bomber Watson_
Posted 18 November 2013 - 07:33 PM
IMO the lock plates would be another surface trying to slip under the torque of the bolts head and would increase the problem if anyting.
Again, just theory.
Cheers.
_tryhard_
Posted 18 November 2013 - 08:05 PM
also the thickness of the lock tab plates might space the bolt heads back just far enough to hit the clutch as it spins loosing the bolts
_202DOHC_
Posted 18 November 2013 - 10:17 PM
_Dansthemanow_
Posted 18 November 2013 - 11:25 PM
maybe drilling the bolt heads and using stainless lock wire mite be better than tabs?That is easy with cap head bolts,not so easy with hex head bolts i guess.
"then pray to the fly wheel torana god !, offer a effigy of a burning wheels magazine featuring a datsun 260 z motor that does not have any of the current problems a holden 6 has"
Dont worry,theres one datsun guy on this forum who had to dowell and lockwire his flywheel as well!
Forum Fixture
View Garage
Posted 19 November 2013 - 05:57 AM
_Dansthemanow_
Posted 19 November 2013 - 08:40 AM
_Agent 34_
Posted 19 November 2013 - 04:51 PM
http://www.gmh-toran...monic-balancer/
Maybe something like this may help.
waz
there was some discussion with the guys last nite about building a damper from scratch as they have done this before. be he says's it's about a 1000 buck job. he wouldn't tell me what damper he used. but i clearly remember the one you built and was searching for it last night .
so you have to;
buy the damper
machine up the adaptor plate
knock off the timing mark and re weld up
tap the crank as a bolt to hold on balancer
make up new timing marks
extend the alternator bracket
no change to the water pump ?
no room for fan
there is a question i have here and it relates to the use of long and short water pump noses , i assume you have gone to the long nose to accommodate the extra balancer depth and thus no room for the fan left
G
Edited by Agent 34, 19 November 2013 - 04:52 PM.
0 members, 1 guests, 0 anonymous users
