FE-FC Holden Discussion Forum

Hi,
 I'm getting a new cam, lifters and head put on my 179 next month and also have a new set of strait cut timing gear that could be installed.

I've had a chat to the engine shop and they tend to think the strait cuts will drive me crazy with the sound!  

Is it really that bad and does anyone have an opinion whether they are necessary?

cheers
Dave

yes they are noisy, but they wont drive you crazy, the question is what will you be doing with the motor, and how fast will you be goin?

I just like to do things properly the first time.  The stronger everything is the better, that way I can drive it whichever way I choose...  now or in the future.

The driveline and rear end will eventually be toughened up over the next few years so I may as well start with a strong motor.

As long as it doesn't wake the dead or embarrass my girlfriend too much to the stage where i need to get the windows tinted I'd like to use them.  Any other opinions?

Dave

I have straight cuts in the 202 that's in the FE, the motor was previously in an LJ Torrie daily driver. I love the sound and spent most of my driving with windows open. When I had enough I cranked up the stereo.

If you hate the sound of straight cuts, gear drives or blown motors, then yes it will drive you crazy.

If you don't mind the sound, you'll get used to it after a while.

If you love the sound, you'll think it's not loud enough  ;D

I was talked out of going a lot wilder with my motor when I built it by parts suppliers, I later regreted it pretty bad, this time I will ignore all that crap.
I had a mate who fitted straight cuts to his EK and wasn't happy so he also fitted a gilmer drive wich kept slipping off.
the lower resistance is pretty small and they aren't much use unless you are chasing every half a horse you can get, main purpose is for noise.
remember, if it's too loud your to old.

yes straight cut gears main purpose is noise, also with the gilmor belt drives they are awsome, the old ones were shit but the new ones look and sound great, hasnt slipped off once and thats on a 350!!!

cheers
torque

Ive had staight cut timing gears on both 6's and 8's and loved it but remember you also have to put the same gear on the crank which you need a hydraulic puller to remove the old one if you are doing it in the car this may be very difficult but if you are rebuilding the motor any machine shop should be able to do this for you

Hope this helps

Ben

thanks ben,

The machine shop said it would't be any worrries to do it in the car - removing radiator and grille and jacking up engine.  You would assume it would be difficult with the engine in the car though?

If they can do it I may as well put the gear in as I already have it, if not its not the end of the world.

Cheers
Dave

It will be cheaper to just stick a cat under your bonnet and stick its tail in the fan belt !!!
8) 8) 8)

straight cut timing gears are crap as the engine shop said, let me save you finding out yourself, ill give you $90 for them if they are new.

Hey Leon,

I'm not quite sure what you mean?  I was just told they were noisy, and thats what everone one else said too, although some like the noise and some don't.

I think I paid about $130 new, why are you after them if they are crap?

I'm not having a go at you, I just wonder why you think they are "crap"?  Aren't they used on race cars?

Cheers
Dave

My understanding of these gears is that they reduce power losses compared to the normal gears. This is why they are used on race cars, not because they sound good. This is why gears on production cars are not straight cut, because they are noisy.
Colin

Hi.
I think they are also a lot stronger. Being cut straight, they are less likely to have a weak spot & most of the face makes complete contact (If you get my drift?). The standard gears, tend to have areas where not all of the opposing gear actually makes contact, putting more stress on that spot.
Have you ever heard of the "GM Muncie Rock-crusher" 4 speed? Mega, MEGA strong gearbox built for the BIG block Corvettes. LS7 motors (427 Cube, high octane fuel, 500+ Factory HP). They used all straight cut gears internally. They were as noisy as hell & thus earned the nickname "Rock crushers".  These things were STRONG!!

Dr. Terry, help us out here, Mate. Is this correct?

Rob J

Thanks Rob and Colin, thats what I would have assumed too.  The standard timing gear for a red six is only about $30 or $40 dollars I think, and I've heard a couple of old cars with strait cuts and don't mind the whine... sounds a bit trick!

Would like to hear Dr Terry's opinion too... have heard about the Muncie "rock crusher" - I've heard it referred to as an M22 - is that possible?

Cheers
Dave

Hi Guys.

What we have to do here is to discard the myth & discuss why they make straight cut gears.

When gears drives of any type were first invented, they were all straight cut. The available machining techniques were primitive & that was the best there was. The gear tooth was designed in various styles, involute & stub involute etc, but they were all straight cut. But of course, they all were noisy.

The helical cut was developed over time, its main advantage was low noise, in most cases almost silent, people used to pay extra for this. Most factory gear sets, wether they be transmision , timing or diff gears are helically cut because they are quiet & long wearing. The only problem with with helically cut gearing is that it is more expensive & is slightly weaker in outright strength, only becuase when you cut the gear on the angle, the tooth profile the is slightly narrower.

Ever noticed, how, with manual transmissions they are quiet in the forward gear but noisy, but noisy in reverse. Reverse is usually straught cut, because of cost & it isn't used very often. The Muncie 'Rock Crusher" is so named because its gears are very big, very strong & all straight cut, homologated performance use only, too noisy for normal street use. (Yes Chev use M20/M21/M22 etc as sales option numbers for their manual transmissions as well).

Getting back the straight cut timing gears, AFAIK the main reason there available for street engines on the performance market is because they are sh*t cheap to manufacture, & they use the straight cut bit as a strength/performance marketing angle.

When was the last time anybody saw a metal timing gear gear break because it was too weak ?. Sure the fibre ones die of old age or when overstressed or overevved, but not a helical metal set.

For my money steer clear of so called performance straight cut timing gear sets & spend your hard earned cash on something that will give you more performance or more reliability, not because the noise is cool.

Dr Terry.

Thanks for that, Doc!
Man, you learn something everyday on this forum :D.
Regards,
Rob J

I thought straight cut gears would have less rolling resistance, I always assumed they would wear faster and the noise was the teeth meshing and grinding together wich sometimes made me wonder if they really could be rolling more freely.
I am not to worried about the wear as I pretty much replace everything when I pull the motor apart.
does any one know if straight cut gears roll more freely?

Here's a piece of trivia for you - the Citroen logo represents a double-helical gear, the manufacture of which (in steel, anyway) was invented by Andre Citroen.  Here's a rather large pair ($2).

cheers
RET

WOW      RET

  Would like to see the "motor"   THEY came out of  
        ;D ;D ;D :o :o :o ;D ;D ;D

Norm   :)

I wonder what the advantage is of the double helical gear, my guess is that it is to reduce the pushing out pressure of helical cut gears wich is were I think you loose energy.
I wouldn't really doubt much of what Dr Terry says as he seems to be pretty much the most clued up on this forum when it comes to mechanical stuff.
but I think there would have to be a advantage with the straight geras as the helicals even at 2:1 would be quite loaded once we fit double valve springs wich I think would make them want to push apart under load.
when you are chasing all the hp you can I still think straight cut gears are a advantage other than just strength.
has anyone tested this?
anyway, do you want to sell them?

Hi Guys.

The more the angle of the gear cut, then the longer the tooth & then more side loading is put onto the thrust plates of the gears. This is where any frictional losses would occur.

The slight angle difference between a genuine Holden timing gear set & a straight cut gear set is so small you would be measuring the loss difference in milli ergs not hp.

Gears sets of any type will have slight losses. In drag racing, I've seen comparisons done on V8s (with very heavy valve springs) between the standard timing chain set-up, straight cut gearsets  (Pete Jackson style), Helical cut gearsets,  & notched belt drives (Gilmer style). The only one shown to have any advantage was the notched belt drive.

This is in Pro-Stock racing, where they spends hundreds of dyno hours for minor hp increases.

Supercar V8s also use the notched belt cam drive.


Dr Terry.

Hi,

The benefit of double helical cut is that it neutralises the thrust or sideways force of a single helical cut gear set that Dr Terry mentions above.......by having equal but opposite thrusts from the two sides of the helical cut teeth.  

So the tendency to create sideways thrust, particularly for large gear sets like the one in RET's link, is all but eliminated....meaning that the thrust bearing duty/wear is very much reduced or possibly eliminated, depending on what other forces are at play in the design of the gears....

Brad

The muncie rock crusher isn't 100% straight cut.  The gears are on an 18 degree angle which is less than the regular muncie.

I am now at the stage were I need to purchase timing gears and have had to look into it myself.
while the old alloy helical gear was good it only has one keyway.
after talking to my engine guy this morning he said that there may be helical cut gears that are adjustable but if you get straight cuts they are usually adjustable with extra key ways, without this I cant dial in the cam.
I guess that is something to look at if you are building a hotty.
I went down to robbo's this morning were I knew they had straight cut gears for $99 but when I got there I noticed they didnt have extra keway slots, bugger.
so now I am in the market for a new set of timing gears.
while at robbo's I saw some older holden stuff there that you wouldnt see in auto 1 or supercheap.
It was a tiny shop but there were chromed bits hanging up as eary as FJ, also a nice new chrome grey rocker cover behind the counter and a grey harmonic balancer was in the front window.

Diecrest Engineering make (or made) the adjustable straight cuts.

Details are from the Hot Rod Internet site so they may be out of date.

Diecrest Engineering
Bagshaw Street, Harcourt VIC 3453
Ph: 5474 2321 Fax: 03 5474 2536