Tom928

Hi everyone,

I need to perform the TB/WP service on my 81 this winter and I have been looking for information about converting the old style timing belt (square belt tooth) to the newer HTD syle (rounded belt tooth). One of the reasons I am considering this is that I'm finding that some of the old style components are NLA (crank gear - new is NLA, used is available).

I understand that changing all the gears would be a given and I would have to use the newer belt from this point on. I'm not sure about the tensioner, but think it would work for either design.

Has anyone BTDT with success or can tell me why I should not do it?

Thanks,

JP Rodkey

BTDT. Straight forward, and you have the necessary gears (assuming you didn't forget the oil pump). Other than the gears, there is no difference that I can remember.

Garth S

IMHO, this is a good thing to do.

Did this switch to HTD a number of years previously - easy to do: on my last TB replacement, I further added the updated rear cover, lower idler roller, and the '84-'85 tensioner/matching arm & idler/low tension alarm.
If/whenever the original water pump dies, I will further update to the S4 pump w. the more robust pivot stud, S4 tensioner, double lower idler and later 32v center cover - again, all parts are a direct swap: the trick is to line up the correct pieces.

Jim bailey - 928 International

Well said..."all parts are a direct swap: the trick is to line up the correct pieces."

Tom928

Thanks for the feedback.

JP - I thought it might be straight forward - new gears and HTD belt; however, just want to be sure.

Garth - Sounds like you have upgraded everything. Maybe next time I'll upgrade the tensioner - If I can find an 84 tensioner in reasonable condition at a reasonable price I may do that also. But just gears and belt this time around.

Thanks,

GlenL

Funny, I went with the later tensioner and kept the old belt. I don't see any technical reason to change. I've acquired some extra pulleys so no worries.

PorKen

I've got an '84 tensioner I'm not using anymore.

If you want, you could put in adjustable HTD gears, and borrow my 16V tools for the install, until I make new ones. Just have to rustle up some 32V gear hubs to machine.

Tom928

GlenL - interesting - I understand that the HTD belt is better for loading on the belt teeth - one of the reasons I am upgrading. Also, some parts for the early cars are becoming hard to find. The crank gear is a good example. I hope to add a few years of parts availability by upgrading to the newer design.

Ken - Hmmm... I could use the tensioner; however, not sure I want to go all the way with the adjustable HTD gears this time. What kind of condition is the tensioner in and are all the parts there?

Garth S

I also have another '84 tensioner - but I'd have to check the parts bin to see if a matching carrier arm was there: Anyway, my intended point is that an upgrade of the carrier arm is a good idea - and can be done even with your '81 tensioner. This will allow the upgrade to the larger diameter bushings for the pivot bolt from the split white teflon sleeves which are likely present.

GlenL

I plan to update the arm pivot to the later style. That has a brace fromt he WP to hold the outer end of shoulder bolt.

Garth S

Not quite .... that requires the S4 pump, pivot stud ( vs. bolt), and the matching carrier arm: as that arm has a different offset and idler arrangement then add the S4 tensioner, idler, center cover, etc.
These items all bolt on to the earliest of blocks - but it is difficult to select just one element.

Tom928

Garth - I can see your point about the pivot bolt for the updated carrier arm. Does that mean changing the idler?

I think first, I convert over to HTD gears, add a lower roller assembly with new rear cover and get that working.


Thanks guys for all the help,

Andre Hedrick

Okay, I am collecting parts now to do this conversion, will an 85 and newer TB tensioner work with an '81 block and '84 gears?

marton

according to the WSM just change the gears.

Thought about doing this upgrade on mine but was not sure about the benefits.
If, for example, Porsche said that the new belts could be changed less often...

Of course if I did need a crank gear and it is NLA then it would be a good reason to upgrade.

Marton

ceedee

if messing with the Tb wouldn't be so scary , i'd do that , too
gotta give it a think
but great project