My ‘66 98 has an original block & heads (bought new by my dad) 425, now displacing 455 cu.in.

At last rebuild about 10 years ago (by Mondello of Paso Robles, don’t this.) a JM 20-22 cam was installed which Lynn said at the time is supposed to have a “slight lope”. He installed a cam for a 45° block, but it’s never idled to my satisfaction.

I’m wondering if any of the externally visible block numbers can tell me whether it is a 39° block or a 45° block. Were all the ‘66 425’s the 45°?

Back in the 80’s I had this problem and the builder replaced with the correct bank angle cam, but I can’t remember which way it went. But I remember it ran terribly until the cam was switched out.

The lack of smooth idle could easily be a cam that’s just a little too aggressive for a 98, but I’d like to rule out the lifter bank angle possibility.

Many thanks for any insights you can offer. I’m pretty sure it’s just too big of a cam, but don’t want to dismiss the wrong-bank-angle possibility.

Chris

 

It's not your lifter bank angle, that issue is very noticeable.

 

I am of the belief that the 45 degree lifter bank is ‘65 only . That the difference in the ‘66 up is the two possible lifter diameters.I believe there is a few posts to clarify.

 

It can be said all 66 425's that are not Toro engines have a 45 degree cam angle. It was in 67 that 39 degree 425s were used. All 66 and 67 Toro 425's had large lifters and a 39 degree cam.

 

The information you’re giving me is very helpful and it fits well with my previous experience. Many thanks.

So let’s aim at the idea that I’ve got a 45° LBA 425 from 1966 that is not (and never was…) a Toro motor.

That points me toward the cam. The one in there, i believe, has these specs:

JM-20-22 Hydraulic Camshaft

• Street Cam, 1400-5800 RPM Range
• 0.496 Intake lift / 0.520 Exhaust Lift
• 300° Advertised Intake Duration/310° Advertised Exhaust Duration
• 224° Intake Duration @ .050 / 234° Exhaust Duration @ .050
• 112° Lobe Separation

Should I expect a slightly less than smooth idle in return for better midrange? I always thought that was the trade off, but I could be mistaken since I’m not really an engine guy.

Next I should mention that I seem to recall there might be roller tip rockers in that engine. If one or more of these isn’t functioning properly, or if I have a bad lifter, could those be contributing to a rough idle too?

It could just be that I’m getting older and have a different tolerance now for a rowdy cam than I did 10 years ago.

Many thanks in advance for your experience, views and thoughts.
Chris

 

Chris,
You may be able to smooth the idle a bit by playing with the distributor advance. My 350 engine has a 217/221 cam and the idle was a bit rough with bouncy vacuum. I found that advancing the initial timing from 10º to 18º smoothed the idle and increased the vacuum, then connecting the vacuum advance to manifold vacuum made a bit more of an improvement.

 

The cam you listed is nothing more than a remake of a host of generic cams.
it will not have a smooth idle. However make sure you don’t have any vacuum leaks etc before you give into the engine.

 

Chris - Yes, the external block casting letter can tell you whether it is 39° or 45° with the aid of the attached chart I am providing. According to this chart, a '66 425ci could be either a 39° or a 45°. I hope in your case your block is a 39° because I believe the JM-20-22 was designed for the 39° lifter bank angle. I have the same camshaft in my '67 4-4-2 with the 400ci (39°), it's lopey, but doesn't struggle to hold it's idle. Hope this helps.

 

Chris - Also see this CO post on how to locate where the "Drill Spot" is on a 425 block, if there is one.
https://classicoldsmobile.com/forums...ill-hole-9281/

 

For the record. The wrong bank angle makes the engine into a 375HP paint shaker. There is no way any sane person would let that run more than a few seconds. It cannot be mistaken for a rough idle. Don't ask me how I know.

 

Take that table with a grain of salt. "Solid main webs possible" should be your first clue.

 

Joe - Is any of the info/specs in the BBO section of the table related to the OP's post incorrect? I was hoping it would help him determine exactly what he has.

 

There's a fair amount of anecdotal evidence that links the drill spot to the 0.921" lifters rather than CBA. The only foolproof way to gauge CBA is to measure it.

 

Joe - Thank you!

 

what are the measurements for each block ? . if you do not have one to compare it with

 

Unfortunately, core shift can cause a lot of variability in measurements. I've found that the best way to check this is simply to use one of the lifter angle tools. The lifter bore centerline is either parallel to the cylinder bore (and normal to the deck) or it isn't. That's pretty easy to see with the naked eye.



Alternately, one of these protractors works too.

 

Many thanks guys for the pointers. I like the simplicity of parallel or not.

I’m leaning towards the cam since it idles, not like a paint shaker, but just rougher than I’d like. I had the paint shaker experience way back and this ain’t it.

If I go down the route of changing out the cam, I’ll need to confirm the angle one way or the other. Now I’ve got some clues as to how to do it.

Chris

 

Hi All.. been a long time since I have posted on anything.... If I may offer my two cents based on what I have read here and my own experience...

I own both a 66 Toronado and a 67 Delta Custom coupe. Both cars have the 389244D casting 425. The Toronado engine has the drill mark, and I believe after all I have read that the drill mark denotes the larger lifters and possibly other mods the Toro block has including the 39 degree cam bank angle. The(my) Toro was built the 2nd week of June of 66 (06b) In other words, the drill mark denotes a Toronado engine.
The 425 in my 67 Delta is indeed a 39 degree cba, which I was able to verify with the image showing both castings. The car was built on the 2nd week of November of 66 (11b). It does not have the drill mark.
With this, some of the info in that engine chart pertaining to the 425 engines may not be accurate as Joe states.

Hope this info helps...

kj

 

Do a simple compression test and compare right bank to the left.

they will be significantly different (if the engine is healthy) from one side to the other if the cam is wrong for the block…like 15 to 25 lbs.

this is so easy to do.

and no, having the wrong cam in the wrong block won’t screw it up enough to make it un runnable or idle so whacked out you can’t stand it.

 

I've put a 39 degree cam in a 45 degree block. Trust me you can't stand it. No one in their right mind would drive it that way. I've described it as a 375HP paint shaker.