skpyle

Good Morning, Gentlemen,

I have put just under 1000 miles on the Red Witch since she had a new Porsche timing belt installed, as well as rebuilding of the tensioner and replacement of the rollers and bolts. I have keep the tach at or below 4000rpm, and driven like I have some sense (Other than the brief, yet glorious, 5000rpm blast when downshifting on the highway yesterday.)

I have been researching when to retension the belt. I have seen two general consensus: 1000 miles or 1500 miles.

I have no problem waiting for 1500 miles, however, I have an opportunity this weekend. I have read that it greatly increases working real estate to drain the coolant and remove the radiator hoses when working with the belt. This weekend, I am overhauling the AC system, and will be draining the coolant and removing the radiator hoses to increase working real estate for getting to the AC fittings. This sounds like a perfect time to retension the belt. I have the Jay Kempf tool and Rennlist handy.

However, is 1000 miles premature? I don't think the belt is a Conti, it might be a Gates. It was sourced from a Porsche dealer via Auto Assets, part number 928 105 157 00, Timing Belt.

I won't lie to you. I really want to start winding this 32V V-8 up to 5000rpm. SITM is coming...
Yesterday, when I downshifted on the highway, the tach hit 5000rpm, and the exhaust just snarled. It sounded wonderful. I briefly held 5000rpm then eased it back down to 3500rpm. No snap back.
I want to retension the belt so I can safely wind this engine out, but not before it is time.

So, Oh Wise Ones, please advise this newbie...

Thanks!

Seth K. Pyle

FredR

Seth,

Who advised you that you had to hold back on the revs whist the belt beds in? As I am concerned this is mechanical nonsense. The sooner you wind it up the sooner initial stretch will take place I would think.

Indeed the belt will stretch slightly during the initial period of operation but it is not like bedding in a ring set and if anyone thinks it is I for one would welcome an appropriate education given I have never seen or heard of such in 17 years of 928 ownership- but always keen to learn.

1000 miles should be plenty to bed the belt in unless the "timid driving style" precludes such. 928 motors like to be revved, just get the motor fully warmed before you "give it the berries".

To adjust the belt tension there are two schools of thought - do it properly in which case you need to create clearance to work in and that is best achieved by removing the fan shroud assembly, no need to remove the hoses but if you are going to remove them even better for working clearance.

The other approach is to simply tension the belt the equivalent of 1 bolt flat tighter [this is what an ex factory mechanic advised me they do believe it or not]. To be clear, I am not recommending this but it kind of makes sense.

Similarly, I have pulled the a/c compressor without draining the coolant and disconnecting the coolant hoses - getting things out of the way helps but in this case not necessary or so I would suggest.

Just drive it like you stole it!

Rgds

Fred

StratfordShark

That suggestion to tighten one flat and not remove anything is a potentially very convenient tip!

I know I didn't have to retension my last belt more that 1/4 turn, so a flat would have put it in high end of window.

I find there's enough room if I do want to take off RHS belt cover by taking off top hose after draining a little coolant (popped back in subsequently). I can never remove fan shroud without removing that hose though, so for me would be a Catch 22 to create the room that way without removing hose! The shroud is hard to maneuver up and clear with hose in place.

worf928

I don't know where you got that, but that's very poor advice. It sounds like something a hack mechanic would recommend.

Tension with the proper tool or not at all. Wear of the sprockets and other belt system components is minimized with the belt in the tension range. The belt check interval is not a "tighten the belt" interval. It's a "check" interval. Did the belt stretch? Too little? Too much? Other issues? The purpose of the check is ... to ... check the system not just blindly tighten the belt.

On pre-mid-'87s without the pivot bolt cross brace, it is even more important to not over-tighten the belt.

OP: check the belt tension when you have it apart for A/C. If the belt needs to be tightened and there's nothing else wrong then your good. If there's no or minimal stretch then you'll need to do it again.

I, generally, am not satisfied until I do two belt inspections at least 1000 miles or 6 months apart with no tension change.

FredR

Adrian,

I was advised it is possible to remove the stock fan shroud but it sure looked very difficult to do with hoses in situ as it were [or so I remember]. Not sure I understand why you would need to undo the top hose to get the timing belt cover but then my setup is different. I have the Spal dual 12 inch fan module. This is narrower than the stock fan module and it is literally "Gone in 60 seconds".

My very first TB/WP job on my late 90 S4 was done by the main agents many years ago after my impeller let go. After 1000km or so I took the car in to have the belt re-tensioned thinking it would be an all morning affair after having left it overnight but they let me drive it straight into the workshop and they did it there and then in the manner described above- no issues and all over in 10 minutes.

Rgds

Fred

buccicone

Porkentensioner...............in the future. No need for all this bull***t.

SeanR

Very good advice, spot on.

bureau13

FWIW, OP has an '86.5, there should be no need to fiddle with hoses to remove the fan shroud....at least, on my (same awesome year ) car, I don't have to. Pull back the intake tubes, two bolts, pull shroud.

I'm glad to hear there is no 'baby the car for 1000 miles" rule....because I certainly haven't!

Seth, I'm sorry to hear you haven't been living in the 4k-6K range. It's glorious! Go get some!

Imo000

Who told you not to take the engine past 4K before the belt check and what was there explanation?

GlenL

1250.

Ok... Anytime after 1000 that's convenient for you.

Popular alternative: wait for the warning light to come one, panic, and then tighten it.

skpyle

Damn. Now I feel dumb and cheated. We will fix that tonight on the way to work...


FredR: PO and the gentlemen at Auto Assets recommended I not beat on the engine until the belt had taken a set. I've never had anything with a timing belt, all chain or gear. That, and I was a little nervous facing a 500 mile trip. So, I listened. I got it in my head that winding the engine up without the belt taking a stretch could cause it to walk off. (Me = naive.)

It has definitely been timid driving style, only once above 4000rpm, one blast to 5000rpm. I will fix that tonight.
I have been careful to ensure the engine is up to operating temp before having fun. Normal procedure is start and idle for a few moments, pull out of the driveway easily, shift up through the gears to 3rd at around 3-3500rpm, then get on the highway and cruise around 70mph. Once the temp gauge is at the first line, I am comfortable to go up to 4000rpm as required.

Ah...good to know about not having to drain the coolant and pull hoses for AC work or timing belt retension. I will figure it out when I get in there. I have the Kempf tool and plan on following the procedure.

I will definitely be driving it like I stole it from here on out.



StradfordShark: Thanks for the tip about working with the RHS belt cover. I will figure it out when I get in there.



worf928: Good point about 'checking tension vs arbitrarily tightening the belt'. I will pay attention to that. I will go ahead and check belt tension this weekend when I do the AC work.
So you are saying check tension now. I have have to retension the belt, check again in 1000 miles. At that check, if tension is good, check again in another 1000 miles. If that check is good, be satisfied and go with proscribed interval from there out?

Thanks!



FredR: That brings up a good point. Most of the belt guides I have seen have been written about an S4. I need to keep searching and find a guide for an S3.



buccicone: Yeah...I am kicking myself for not at least asking Eduardo if they would consider installing one when they did the work. Next belt change, Porkentensioner goes in.



SeanR: Yep, I am filing that away as something to learn and pay attention to.



bureau13: Thanks for the heads-up about the relative ease of pulling the fan shroud. I will find out starting Friday.

No baby rule. Just a baby driver.
I will now spend quality time in the 4-6000 neighborhood on the tach.



Imo000: Combination of PO, shop, what I thought I read, and general naivety on my part. I thought the belt would walk off the gears, particularly if allowed to snap back resulting in rapid drop from high RPM.
I am learning.



GlenL: As of today, mileage is 1006, and will be around 1150 by Friday. So, I am comfortable checking tension this weekend.
I'll pass on the 'popular alternative'. Trying to avoid expensive meeting of valves and pistons.


Thanks for your advice and experience, gentlemen!

Seth K. Pyle

FredR

Seth,

Good attitude.

Now that we know you have the Kempf tool you have no excuse for not using it. Some will tell you to set the belt at the top end of the range but I personally recommend to set it dead centre but whatever.

What many do not know is that when Jay was developing this tool he found to his surprise that the tool Porsche specified for use had very poor repetition characteristics and that the tool he produced gave the same results every time. I have no position on this matter and take the view that if the likes of Roger and Mark endorse its use that is good enough for me.

For purposes of completeness just make sure that when you do check the tension you must do so with No1 cylinder [not no 6] at TDC on its firing stroke, move the engine forwards two complete revolutions and check again for consistency.

What happens after a new belt is fitted is an interesting discussion in its own right. New belts stretch a little- that is a given and predictably so. Once this initial stretch has taken place it should not stretch any further and if it does then that suggests something is not right.

Belt pre-tension is important because the belt stretches under load as it pulls on the cam wheels and given it travels a fixed distance, as the loaded side stretches the other side slackens by the same amount and the tension applied is intended to ensure there is no back lash to flap around and jump a cog. On our stock tensioner this is achieved by the correct pre-load and if you can get it correct to within two or three flats of the hex bolt you are probably doing well. Now there is another alternative designed by Mr Porken - the PKTensioner. This is very popular with many and is intended to be a fit and forget type of thing with nothing to measure or adjust relying on constant spring pressure to achieve the need. The relative merits have been discussed hotly. I take the view that I am currently happy with the stock system and feel comfortable knowing I have the low tension alarm [not that I have ever needed or seen it flash in anger].

Finally, I change my belts every 6 years regardless of mileage. I believe they are no where close to being done but given the ambient temperatures my 928 sees during summer use I stick to the interval recommended by Gates themselves.

Rgds

Fred

vanster

What's a timing belt?

zekgb

It's tight, but the S3 RHS belt cover comes off relatively easily by just removing the intake tubes, cap and rotor. No need to remove the upper radiator hose or cowl cover if you're not in there for anything else. Don't forget the coil ground when you reassemble.

M. Requin

You need a copy of John Kelly's Timing Belt Manual for the 85/86... - do a search on that and perhaps you can find a copy. PM me if not.