: Longevity of the N* timing chain nylon tensioner pads ?



peteski
06-21-04, 03:08 AM
Quoting BBOB from one of his recent posts on the 4.1 forum " If it is a Northstar (and this post is in the wrong section) then it has overhead cams, chain drives that never need replacement and no V-belts.....just a single serpentine belt drive for the accessories.".

That is nice to hear, as my Eldo has almost 110k miles on it.
But reading the FSM, N* uses nylon pads on the tensioners as the contact surface with the chain. Somehow when I thing about steel rubbing against nylon - I see wear... I also hear all the horror stories with nylon timing gears on other cars.

So, I wonder how long the nylon pads last. Also, what happens to the shredded nylon ? Ends up in the oil filter ?

I'm surprised that Cadillac didn't have a better solution than nylon pads.

Peteski

BeelzeBob
06-21-04, 05:57 PM
Read the service manual again...and look at the pictures.....if you look at the timing drive carefully you will see that the "pads" on the cam chain tensioners press against the chain guides...not against the chains directly. On the primary chain there is a nylon shoe that acts against the primary chain directly but it is fairly large and thick.


What better material would you recommend...??? I'm all ears......


The nylon guides last forever. The guides are smooth when new and are quickly "marked" or grooved slightly by the chain side plates and then they stay that way forever. Once the rollers of the chain roll across the nylon surface there is no more marking of the nylon.

I have never seen nylon bits floating thru the engine. I think the nylon flows or creeps at high temps and pressure from the chain links to form the grooves as much as it "wears"..... I suppose if there were any nylon bits loose in the oil they would end up in the filter but who cares....they are harmless anyway. A microscopic piece of nylon like the cam guide material is not abrasive and is totally harmless in the oil.

Different situation with the nylon on the cam drive gears from cam in block engines back in the 60's/70's/80's.... "Nylon" is a somewhat generic name used to describe a whole family of materials. The stuff on the cam chain guides for the Northstar is FAR more durable than what was available for cam gear teeth decades ago. Besides, in those applications there was much more impact energy onto the nylon surface from the chain teeth engaging it...not just gliding over the surface. Besides, even in that harsh situation, the gears would last 100K or 10 years in the worst cases...and some of them are still running OK after 20 or 30 years.....

The guide surface that actually touches the chains on the Northstar isn't actually heavily loaded. Think of it like a bicycle chain. If you turn your bike upside downwards and work the pedals the chain kind of jumped around and shook and such.... If you just gently laid your hand on the chain while it was moving it wouldn't hurt your hand rubbing on it and the chain would quiet down with the gentle dampening of your hand pressing against it. Same with the nylon chain guides. They are shaped to the shape the cam chain naturally assumes when the chains are in motion so the guides don't absorb a lot of force or really do much. They are just there, protected by a heavy oil film, to guide the chain and dampen any movement of it.

Your critism is not well founded.

Not only "Cadillac"...but every engine maker in the world uses those type of guides for cam chains. There is simply nothing better for them. The self lubricating characteristics and dampening characteristics of the material (known as "nylon") on the chain guides provides excellent wear and durability while being quiet, trouble and maintenance free.

peteski
06-21-04, 10:41 PM
Hey BBob - I wasn't criticizing anything - I was merely curious.
Thanks for your thorough explanation.

I never had the engine apart far enough to see the details of the tensioners (and FSM pictures aren't all that clear either).

I also thought that the pads were rubbing against the outside of the chain. I didn't realize that they wore down enough to contact the chain rollers. Rollers contacting the nylon is a perfect solution - and you are well aware of it (I wasn't before this post).

And of course you thoroughly explained how the nylon wears and that there is no danger of any floating nylon bits.

Yet again, I have learned another interesting item in engine mechanical engineering.

Thanks again BBob !
Peteski

Privateer
06-21-04, 11:25 PM
Very intresting question. One I have thought of a few times myself. A few years back I went to a car show in Tampa, Florida. At the time I did not own a Cadillac but was very impressed with the presentation of the Northstar engine at the Cadillac display and took these pictures of a cutaway display model. I was really impressed with the engineering and quality of the construction. Take a look.

Rich_M
06-22-04, 12:02 AM
I've had some engines apart over the years. That one is beautiful and well constructed. Thanks for the pics.

Regards,
Rich

BeelzeBob
06-22-04, 12:48 AM
Those cutaway show engines are very nice and informative...just remember that the marketing guys consider them "jewel" engines so everything is smoothed , chromed, painted, etc....LOL.


The tensioners in that cutaway are fully retracted and there is slack in the cam chains that would not normally be there if the engine were operational and running. The chain span between the two cams shows a bit of droop that indicates slack that would never be there.

Regardless, you can see where the tensioners push against the movable guides on the curved section and the fixed guides on the straight sections of chain that are always in tension. There was a lot of development into the shape of the curved guide to properly tension the chain , dampen it's oscillations and "guide" it in the curve that it would normally want to follow running over the sprockets at 6500 RPM.

cadillacstars
06-22-04, 02:31 AM
unless there is a catastrophic engine failure the nylon guides are bulletproof

peteski
06-22-04, 11:11 PM
Darn !
I can't see any of the images Privateer posted ! :(

"Attached Images" section shows up in the message but it is empty...
I checked my preference and I have Image Viewing enabled...
Go figure...

Privateer, could you post the URL for those images - I would love to see them.

Thanks,
Peteski

97Deville
06-22-04, 11:45 PM
I was able to see the pictures yesterday, (they looked great) but can not see them to-day :hmm:

Nothing changed in my browser, were they moved?
Chris

97Deville
06-22-04, 11:46 PM
They are back,,:bonkers:

peteski
06-24-04, 04:22 AM
:annoyed: I still can't see those pictures ! :rant2:

Privateer
06-24-04, 10:29 AM
I do not have a URL for them. I just have then on my hard drive. I will be glad to e-mail them to you in JPEG format in the posted 640x480 res. or the original 1600x1200.

CAJUN-Z
06-27-04, 09:11 PM
I don't know about nylon in the Northstar engines, but in a past Mustang II and in two Quad 4's, the nylon "shoes" were destroyed and the timing chain went south! Hope the "nylon" is a better grade and attached a bit better than what my experience has showed me...

cguthrie
06-27-04, 11:26 PM
No expert on N*, but have enjoyed 50K of hard miles with no issues, and have heard of zero problems with the nylon tensioners from anyone on this list.

However, if you check the Jaguar XJ8/R list, Jag apparently underengineered their tensioners on the first generation 98-00 engines. I was originally interested in the 98-99 XJRs when I bought my STS, and along with keeping an extra $10K in the bank, am enjoying an engine that was built correctly the first time!

I've seen pic's of the jag's 1st generation tensioners, and they seem to have about 1/5th the mass of the N*! I believe most failures on the jag are associated with a previous overheating, which further weakens an already weak part. Along with infrequent oil changes. Often, the valve train can be destroyed. Apparently even at relatively low miles, like 60K! Very expensive.

I'm feeling good about the N* tensioners...

Chris
99sts 90K

BeelzeBob
06-27-04, 11:39 PM
I don't know about nylon in the Northstar engines, but in a past Mustang II and in two Quad 4's, the nylon "shoes" were destroyed and the timing chain went south! Hope the "nylon" is a better grade and attached a bit better than what my experience has showed me...

The quality of the nylon is important but even more so is the dynamics of the timing drive and the action of the timing chains. There was a tremendous amount of development that went into the Northstar timing drive to keep the chains "quiet" and stable at all RPM's. That is the reason that there is a stepped drive in the Northstar engine with uneven drive ratios between the sprocket sets...to eliminate much of the harmonic content that destroys other timing drives. The design of the shape of the timing chain guides was done to carefully mimic the natural shape of the chains at high speed so the guides act as stabilizers that are actually cushioned by the oil film rather than a "guide" that is trying to force the chain to do something "un-natural"...

The timing drive of the Quad 4 had a lot of harmonic content driven mostly by the fact that it was a 4 cylinder engine with twice the crank shaft degrees between firing impulses. This is naturally much harder on the timing chain as the firing impulses are much less smooth and cause much more disturbance to the chain motion. The guides on a 4 cylinder have to absorb much more energy than the guides on a V8 all other things being equal.

peteski
06-29-04, 04:08 AM
I do not have a URL for them. I just have then on my hard drive. I will be glad to e-mail them to you in JPEG format in the posted 640x480 res. or the original 1600x1200.

That would be great ! I tried to send you a private message but I'm not allowed
:annoyed:

Could you email the original sized pics to peteski7 # yahoo.com
(remove spaces and replace # with @).
Thanks !
Peteski