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270 distributor replacement

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tomofficial2

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I have twin 1984 270's with mallory YL624AV distributors. I want to replace them with a breakerless distributor. Mallory has a YLM624AV can I assume this a replacement for the points distributor I have? gears and all??
 
Why not just install a Petronix module? Much cheaper, and you don't even have to remove the distributors.

Go to their website and check out the products and procedure.

Jeff
 
There is some interesting info on the YLM as of lately.
I love the VR triggering of the YLM..... it is very hard to beat this "Variable Reluctor" type triggering..... Chrysler company had been using this for years, and very successfully.

The YLM 624 AV is for a LH Standard Rotation engine.
The YLM 624 BV is for a RH Rotation (counter rotation) engine.
Both distributors rotate CW, as the engine oil pump dictates this rotation!

The standard AV "drive" and "driven" gears place an "Up-Lift" on the shaft (this is normal), and is checked via the thrust washer immediately above the driven gear.

However, the BV "drive" and "driven" gear combination, places a "Down-Load" on the shaft.

Apparently Mallory has an issue in-that the thrust bearing for the BV is inadequate and/or is non-existent on this 624 BV model!
There have been some wear issues with BV.

Apparently the YLM 619 BV offers the correct "down-load" thrust bearing, but the advance curve is not same as the 624, and would require a curve change, if I understood this correctly.

So, I would make a phone call to Mallory, or a Mallory dealer who is abreast of this, and find out what the fix is.
If a dealer knows nothing about this, then continue making calls.

I still think that the YLM is an excellent choice, however. :)

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As for the Pertronix conversion kit, Jeff, you may not care for what I have to say about the Pertronix, but here goes.... no offense!

These kits are "Hall Efftect" triggering. The magnetic inducers are cast into a plastic unit that fits onto the existing points cam. IMO, they are not as accurate as a VR, for example.

In addition, we are relying on a retro-fit to our potentially worn shafts and shaft bushings and our potentially worn advancing mechanism, and so forth.
If the upper shaft area is worn, this may mean an un-wanted change to dwell while in operation.
(This isn't necessarily a hall effect issue, but rather an issue when using a distributor that may have many hours on it, and have some wear.)

Does the Hall Effect work? Sure it does...... but IMO, just not as well as a VR, or even a Photo Eye, (of which I would also steer clear of).


So if the budget is there, you can't go wrong by giving yourself all new components by installing a complete new ignition distributor..... Mallory or other! The advance curve should be very consistent between the two new 624's.
Set BASE, check and adjust TA, and you're on your way.

Just my two cents on that!
 
Last edited:
RicardoMarine said:
The YLM 624 AV is for a LH Standard Rotation engine.
The YLM 624 BV is for a RH Rotation (counter rotation) engine.
Both distributors rotate CW, as the engine oil pump dictates this rotation!

The standard AV "drive" and "driven" gears place an "Up-Lift" on the shaft (this is normal), and is checked via the thrust washer immediately above the driven gear.
Click to expand...

I'm really confused with this. Crusader BBC gen IV cams all spin the same direction, so why would the BV ever be used?


opps, i see this is a SB thread. Even so, don't SBC spin the cams all the same way for Crusader?
 
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diver_dave said:
I'm really confused with this. Crusader BBC gen IV cams all spin the same direction, so why would the BV ever be used?

opps, i see this is a SB thread. Even so, don't SBC spin the cams all the same way for Crusader?
Click to expand...
If that is the case, then you are correct. Two AV's is all that are needed.

Question: Is Crusader using twin cam gears (2 gears only) on their RH engines these days?
(I.E., maintaining Standard Cam Rotation on a RH engine)
Serious question, as I do not actually know! Most that I see are typical chain drive.


Whether or not the camshaft is chain driven or gear driven, the lobe placement is a such to accommodate the reverse direction of the crankshaft and consequent reverse firing order (since we are using the standard crankshafts).

If we double gear drive the cam, it now rotates in a conventional direction (as you suggest), and the distributor drive/driven gears remain same.
If we reverse rotate the cam, we must change the helical cut of the distributor "driven" and camshaft "drive" gears to accommodate the standard oil pump rotation. (all sbc oil pumps rotate in the original direction, of which means that all distributors must rotate in the same CW direction).

This leaves us with only one option for the distributor drive..... and that is, we reverse the helical gear cut for the reverse direction camshafts.
To my knowledge, there is no other means of doing this!
 
I checked the parts listing. If the Model 270 SN is under 68702, it uses a gear drive on the RH engine so it will use a "standard" disstributor (the -AV part). i didn't check the newer models but I'd suspect all the pre-Vortec SBC stuff uses the gears, like the BBCs.

DD - I looked into this a little bit. Turns out not everybody builts the "reverse" function the same way on the SBCs. Some use the gear drive and some use the chain drive on the reverse rotation products. The gears use the 'normal' distributors and the chains use the "B" type. Mallory would do the consumer and themselves a favor if they recognize this and change their literature to reflect this.

The current GM product line only has LH engines that i'm away of. I've seen several ads for "new" RH 7.4's but no source info is provided.
 
MM- That all makes sense. For the marine market at least, the chained RH motor appears rare. AND, there are some gear driven LH motors, with aftermarket parts,using the idler gear design. Mentioned only for completeness!
 
Concur on the RH chains being scarce. I almost bought the gear drive for the LH one when we did the overhaul - with the twin idler design. Decided it wasn't cost effective.
 
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