Save Your Money- Cam Timing Gears
12-21-2013, 10:16 PM
#46
The cam gears can be recoated as shown, I still have yet to test mine. I also used some 320 grit and a hard steel plate to run the teeth against to smooth the cupping back to flat.
12-21-2013, 10:42 PM
#47
Three Wheelin'
I'd rather have engineering that requires expensive maintenance than engineering where the core design is flawed. For example at the dealer I worked for, we had a brand new Dart in for steering noise. Countless different techs tried finding the source of the noise, pulled the lower subframe out, talked to Chrysler engineering, and long story short we never did find the problem. So the dealer bought it back, as a lemon basically, and in typical fashion put it back on the lot for some unsuspecting buyer. Many many Chryslers have deep down problems that originate with the core design of the product, and of course they don't want to do a total redesign because that would cut into their profits too much. Just look at any of the LH platform cars with their center take off steering racks, they designed it for use with a center take off rack, which has inherent problems used on Macpherson strut suspensions because the tie rods have to take so much load. It only works well on SLA suspension. People have died due to tie rods snapping off, all because of a core design flaw. Has any Porsche had such major fundamental design flaws from the start? I know there's the aluminum ball joint thing but that doesn't count since that's a problem with the choice of material not engineering.
12-21-2013, 11:50 PM
#49
Yes, my opinion from experience with mine I think you can.
12-21-2013, 11:58 PM
#50
Should you? LOL, good question. I can say that I would not recommend that, but if I told my customers yes they can............who would be at fault for doing so. So I say, go for it and let us know how it works in a few years.
12-22-2013, 02:32 AM
#52
Rennlist Member
... The nice bonus with the new gears is they are made of much harder material than the previous soft gears and the hard anodized finish is much harder/resilient than the spray on coating. I am predicting that we will see no wear on the new gears and they will last a long time. Time will tell...
Do you have a link to your new gears? Or a way to find them? Using the Search link to look for "Cam Gear," "Cam" or "Gear" gets nothing. Am I doing something wrong? Wouldn't be the first time.
Will
12-22-2013, 10:30 AM
#55
Burning Brakes
Thread Starter
For the record, my gears (70,000 miles) had some wear in the coating in the center of the teeth, but the base metal was intact and was not cupped. Roger and I discussed, and he agreed that I could run the gears, as-is, for one more round before replacing at the next service. I discovered a post by Stromius where he had his gears coated by Finish Line, and I thought 'why not'?
BTW, therein lies the brilliance of Roger's business: he will offer you absolutely invaluable advice and will only sell you what you really need. The difference here is that the proprietor actually is an active participant in the hobby. When I first bought-back my car this year, I (before checking RL) called one of the big Porsche parts retailers and sought to ask questions before I ordered. The fellow on the phone knew zero about 928's and asked that I call back when the guy who knew about them was in the office later.
Finish Line strips the old coasting and applies their dry film lubricant. I've inspected the gears, and they appear to be perfect. No cupping.
I'll keep an eye on them and report-back periodically. Assuming that you are starting with good gears in the first place, you simply cannot beat $45 per gear for the service and peace of mind.
BTW, therein lies the brilliance of Roger's business: he will offer you absolutely invaluable advice and will only sell you what you really need. The difference here is that the proprietor actually is an active participant in the hobby. When I first bought-back my car this year, I (before checking RL) called one of the big Porsche parts retailers and sought to ask questions before I ordered. The fellow on the phone knew zero about 928's and asked that I call back when the guy who knew about them was in the office later.
Finish Line strips the old coasting and applies their dry film lubricant. I've inspected the gears, and they appear to be perfect. No cupping.
I'll keep an eye on them and report-back periodically. Assuming that you are starting with good gears in the first place, you simply cannot beat $45 per gear for the service and peace of mind.
12-22-2013, 11:14 AM
#56
Rennlist Member
If your inspection and that of the company doing the recoating agree the gears are serviceable then go for it......your car, your engine.
As far as Rogers advice indeed he shares a great deal of knowledge but he also has these sales on parts our cars either need or will need in the future......there goes the Porsche account again
12-22-2013, 12:58 PM
#57
Rennlist Member
If they are in good condition, I get them all coated as this should reduce the T belts running temp.
Automotive Machine here in Detroit area does the coating for 25 bucks per gear, they also do great machine work.
Also don't ever use a chemical to strip them or they will melt
Automotive Machine here in Detroit area does the coating for 25 bucks per gear, they also do great machine work.
Also don't ever use a chemical to strip them or they will melt
Last edited by davek9; 12-07-2014 at 11:55 AM.
12-22-2013, 01:23 PM
#59
Rennlist Member
Like I said "don't use a chemical to strip them", I've seen the stock gears melted using chemical stripers, I certainly would not test it on a good usable set of gears. If you have used "oven cleaner" with good results, than good for you.
I'd rather let the coater do all the work, that way if the coating has any issues they can't come back to me and point to the stripping methods I used.
I'd rather let the coater do all the work, that way if the coating has any issues they can't come back to me and point to the stripping methods I used.
12-22-2013, 02:37 PM
#60
Rennlist Member
This has been true forever, 32v cam sprockets all have oversized keyways. That goes along with the slotted holes for the distributor rotor (and Ken's 32v'r tool), to allow the cam timing to be adjusted.
Agreed, 100%. I think recoating is a great idea, and I really appreciate your posting your experiences.
The only concern I would have is that, looking at the pictures you posted of the finished gears, there appears to have been wear into the aluminum and not just to the coating.
Here's the pic, cropped: The top of the left-hand tooth does show some belt wear.
It is probably just fine but it won't fit the belt as well, or last as long, as a new sprocket. Just keep an eye on things every 10-15K as usual, and watch for any wear on the teeth.
Consider the interaction between belt and sprocket: The fit between the tooth profile and the shape of the belt is important. The tensile-strength of the belt is all in the flat web, not in the teeth-- they only serve to keep the sprocket exactly located, rotationally. For maximum life the teeth need to fall into the grooves on the sprocket exactly, and not be forced into alignment.
But the web of the belt rides on top of the teeth, and as the top of the teeth wear, the effective diameter of the sprocket changes, which changes the pitch of the teeth, on the sprocket. So the teeth on the belt no longer line up with the grooves in the sprocket. This is why worn sprockets chew up belts-- the continually force each tooth to shift a little because the pitch doesn't match. It's not much, but it doesn't take much-- .010" wear would be .030" over the half revolution that the belt engages.
Waiting until the top of the teeth are all shiny is too late, but I think recoating before then is a terrific idea.
The only concern I would have is that, looking at the pictures you posted of the finished gears, there appears to have been wear into the aluminum and not just to the coating.
Here's the pic, cropped: The top of the left-hand tooth does show some belt wear.
It is probably just fine but it won't fit the belt as well, or last as long, as a new sprocket. Just keep an eye on things every 10-15K as usual, and watch for any wear on the teeth.
Consider the interaction between belt and sprocket: The fit between the tooth profile and the shape of the belt is important. The tensile-strength of the belt is all in the flat web, not in the teeth-- they only serve to keep the sprocket exactly located, rotationally. For maximum life the teeth need to fall into the grooves on the sprocket exactly, and not be forced into alignment.
But the web of the belt rides on top of the teeth, and as the top of the teeth wear, the effective diameter of the sprocket changes, which changes the pitch of the teeth, on the sprocket. So the teeth on the belt no longer line up with the grooves in the sprocket. This is why worn sprockets chew up belts-- the continually force each tooth to shift a little because the pitch doesn't match. It's not much, but it doesn't take much-- .010" wear would be .030" over the half revolution that the belt engages.
Waiting until the top of the teeth are all shiny is too late, but I think recoating before then is a terrific idea.