Cam bearings LA vs 360 will LA ones fit a Magnum?

[Bruceynz]

Hi Guys,

Ok I have some PD-16 cam bearings for an LA. I thought the LA and Magnum were the same but the correct part for the magnun is PD-25, I called Dura Bond and they said that 2 of the bearings in the LA are a little wider, apart from that they are the same. I have a set of LA cam bearings here I was going to put into the magnum, will it be ok to use them(PD-16)?

Thanks
Bruce

 

[BudW]

What I found - the PD-16 fits:
'64-69 273 (all)
'56-66 277, 303, 313, 318, 326 (basically all Poly engines)
'66-79 318 LA (all)
'68-73 340 (all)
'71-78 360 (all)

The PD-25 fits:
1980-2003 318 (all, until end of production)
1979-2003 360 (all, until end of production)

What I found out to be different between the two - is the center camshaft bearing – one is wider than the other version. The other 4 bearings are the same.

I would think both "could" interchange – but honestly – I have no idea.

I do know the big issue is to make sure the oil holes do line up. Those oil holes is what provides the only oil supply to the crankshaft bearings.
BudW

Edit: Also, I do know that all LA/magnum camshaft blanks (roller or not) will interchange. The Poly camshafts will fit the LA block but lobes are in a different position (ieieieie vs eiieeiie as well as lifter angle is 90’ vs. 56’ (or whatever degree LA’s are)).

 

[Bruceynz]

do you know how much wider it is?

 

[BudW]

Honestly - I didn't even know there was a difference on those bearings, until you brought it up (so no, I have no idea).

I do know the camshaft blanks (before machining the lubes) are the same.

I would suspect the bearings would interchange and if you already have a set – I would try it (if your tools allow for it) – just as long as the oil holes do line up afterwards (which is not hard to check).

The difference is the center camshaft bearing.

Personally, if I already had a set - I would definitely try it, first - for I just can't see it not working (other than it being wider or more narrow). The center bearing doesn't have the stress as the end bearings have.
BudW

 

[Bruceynz]

This just in from Dura Bond - BTW very helpful company!

PD-16

PD-16-1 width =.875” (22.225mm)
PD-9-2 width =.760” (19.304 mm)
PD-9-3 width =.760” (19.304mm)
PD-9-4 width =.760” (19.304mm)
PD-9-5 width =.940” (23.876mm)


PD-25

PD-16-1 width =.875” (22.225mm)
PD-25-2 width =.625” (15.875 mm)
PD-25-3 width =.615” (15.621mm)
PD-25-4 width =.615” (15.621mm)
PD-9-5 width =.940” (23.876mm)

 

[kkritsilas]

Is it possible to machine the LA bearings down to work on the Magnum? Just an idea to try and reduce wait tome and cost. Obviously won't work if there are other differences like flanges or tapers involved.

 

[Bruceynz]

Engine off to the machine shop today, he is going to see if they will fit with no issues if not will buy some new ones.

 

[Bruceynz]

I am going to throw it out there, are the cam lobes wider on a roller and this caused issued with cam bearing clearance?

 

[kkritsilas]

I only know that the hydraulic lifter cams have a taper on the lobes, that combined with the shallow curve at the bottom of the hydraulic lifters causes the hydraulic lifter to rotate. The roller cams don't have the taper, as this is not needed with them (this would be a very bad thing if the roller lifter were to rotate). I can't say if the lobes themselves are any narrower or wider. I will say that I haven't heard that the cam bores on the Magnum block are any wider or narrower than the cam bores in the LA block. It may be that the cam journals in the Magnum are made narrower for some reason (friction reduction?)

 

[80mirada]

I would bet the journals in the block are the same, they probably narrowed the bearings to reduce cost and/or journal drag. The biggest difference, in the factory bearing were the feed holes to the cylinderheads to oil the rocker arms for LA heads.

 

[BudW]

Magnum and/or roller lifters have nothing to do with the camshaft bearings – sense the bearing change was

The PD-25 fits:
1980-2003 318 (all, until end of production)
1979-2003 360 (all, until end of production)

The wider lobe (if it is wider) and the lobe taper (for non-roller lifters) would not matter in this case.

Personally, I think the PD-16 would work for both – for I’m fairly sure I have seen a bit of block on both sides of the newer bearings – but never really wondered as to why (I’ve not had the pleasure of changing camshaft bearings before – but been in the same room as them being changed).


This has me wondering as to why the change - except for maybe cost.
If cost was the issue, how much money is to be saved on 0.145” times 3?

I looked further and found the block casting numbers did change – so maybe the casting thicknesses are different?
’76-79 318 block casting number is 4006730
’80-83 318 4104230

’76-80 360 is 4006830
’81-85 360 IS 4045601 and/or 4179930 (I can’t read my writing on the last line) and is non-roller.
BudW

 

[Bruceynz]

Ok took some pics, the dirty cam is the magnum cam, the clean is the LA cam, don't laugh at my plastic vernier, works well in my workshop to give me rough ideas, when I need good measurements I have a vernier with a dial gauge Why does the LA cam have holes and the magnum has none? BTW yes its metric vernier, 25.4mm is 1inch 40 thou is approx 1mm that will get you by as a rule of thumb to convert!

 

[MiradaMegacab]

LA cam has holes for 'timed' oil feed to left and right rocker shafts.

 

[kkritsilas]

Just going from appearances, the hole for the shaft oiling in the LA cam forces the journal to be wider. The Magnum cam, lacking the hole, can have a narrower journal. As long as the Magnum journals are in the same location as the LA journals, there shouldn't be any problem. Just by eye, it doesn't look like the lobes are any different in width than the LA lobes.

 

[Bruceynz]

Anyone got an LA and Magnum blocks lying around they could compare or measure?

 

[BudW]

The camshaft blanks (before machining) are the same on LA (roller or not) and magnum’s.

The camshaft bearings (PD16 or PD25) matter not – to the camshaft.

What the camshaft bearings do matter to, is the width of the block casting – that is “IF” it even matters there. Sense the inner and outer diameters are the same – the only thing that would matter is getting the oil holes lined up on block install.

It does matter as to which hole the camshaft bearing goes into – for bearing size does taper (bearing diameter), per hole number.
BudW

 

[Bruceynz]

Picture tells a 1000 words! Look how much wider bearing can fit.

 

[BudW]

That is why I “think” either camshaft bearing set will work.

It is also why I wonder why Chrysler changed to bearing width, to begin with (when nothing else changed).

A person “could” go with a wider camshaft bearing, if a person wanted to (or could find one) – just as long as oil hole matches up and it doesn’t contact the camshaft.
BudW

 

[kkritsilas]

The end result is that the camshaft bearing web is the same between the LA and Magnum, which goes with the idea that the block itself is the same between them as well.

As for the narrower camshaft journals for the Magnum, that is one that only the engineers that worked on the re-design would know. Speculation can be made regarding reducing internal friction, not needing full width because the oiling hole was deleted (Magnums oil the valve train through the pushrods), or even cost savings (less material used on the camshaft and cam bearings). Doesn't really matter, I guess, but it would be nice to know.

 

[Bruceynz]

Hi Guys,

Ok the machine shop called about the cam bearings, well well well you guys will be amazed! The bearings popped in all ok and lined up. Live and learn!