When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Not wanting to start up any more flaming here, but while many have referred to that as a good thing, for me it's an indication that even the designers were concerned about the robustness of their system. Lots of cars have interference engines with timing belts but like you, I've never seen another that felt the need to put a warning system like this in. The most I've seen are simple timers that tell the driver it's time for a timing belt job.
Originally Posted by Ducman82
This may have been asked before, but the 928 is the only car I have ever owned and driven that has a timing belt warning light. Why is that? Early cars do not have that so was it a add on later due to issues?
Not wanting to start up any more flaming here, but while many have referred to that as a good thing, for me it's an indication that even the designers were concerned about the robustness of their system. Lots of cars have interference engines with timing belts but like you, I've never seen another that felt the need to put a warning system like this in. The most I've seen are simple timers that tell the driver it's time for a timing belt job.
Perhaps the designers were concerned with the importance of a loose belt. Do you have a smoke alarm in your house?
Perhaps the designers were concerned with the importance of a loose belt. Do you have a smoke alarm in your house?
Yeah, but I pulled the battery when it started beeping (I'm kidding!).
Clearly, they were in fact concerned about that. The question is why they were more concerned than everybody else (even themselves on other cars). I have my theory of course, as stated above, but it's just a that, a theory, and I'm sure you have a different one.
My original Timing Death thread was closed, so I will post here instead.
This morning I had a free minute or two so I installed the new regular Gates belt (thanks Roger) and after turning the engine over by hand, the PKensioner is extended to 9mm.
The tension light on the factory system trips when the belt is loose, but the factory tensioner is just a threaded bolt that is bolted to the engine. It never comes loose. So the engineers must have designed the tension light to spot a fault somewhere else, like a broken cam, bad oil pump, worn tensioner bearings, failing water pump etc. If you are 100% that all these other items are in good order, then the PKT is a good option. You also have to be more diligent on maintaining these other items if you are going PKT as you don't have a warning light to indicate pending doom.
It's funny in a way, my car came with the PKT. In order to try and make it bulletproof I ditched the cheap Chinese pump installed by the PO and installed Ed's Guardian pump. So at this point I was totally comfortable with the auto tensioner, I had re-coated cam gears, new water pump and a new belt. Then my oil pump goes south, I get so much play in the oil pump shaft that my belt starts riding forward and realistically probably would have been chewed off if I had driven much more with no warning light to tell me something was wrong (I caught the problem by the oil pump loosing prime on startup). Then on reassembly I find my PKT is one of the ones with the longer then average extension and have to make the mods to bring it into spec.
I know Ken was looking at the washer with bendable tabs, but how about make a small run of brackets with the T/D mounts 2 mm closer in and let Roger keep them in stock? If a customer has a car with a longer extension just send back the bracket and swap it for the other one. I would think this would be a rare occurrence based on what I have seen in this thread, and Sean's install history, but at least they would be available.
My original Timing Death thread was closed, so I will post here instead.
This morning I had a free minute or two so I installed the new regular Gates belt (thanks Roger) and after turning the engine over by hand, the PKensioner is extended to 9mm.
Exactly where mine installed at last week with a new Gates belt before I modded the T/D.
Doesn't it look like a lot of room in those valleys?
As discussed in the other thread - I'd say the gear was flipped over so that the previously pulling/worn side was now the trailing edge - or it was just plain worn - if the engine rotated backwards, there was not much purchase, especially without the roller.
Doesn't it look like a lot of room in those valleys?
As discussed in the other thread - I'd say the gear was flipped over so that the previously pulling/worn side was now the trailing edge - if the engine rotated backwards, there was not much purchase, especially without the roller.
Is it me, or does the timing belt design of the 928 have a low amount of belt wrap on the crank gear? The cam gears which have double the teeth and less then half the work of the crank gear have almost double the amount of belt wrap.
I wonder if Porsche ever considered putting an idler in between the oil pump and the crank gear to increase the wrap? It certainly would have to be robust being on the side being pulled by the crank.
Unless I missed something I have still not seen a credible explanation of why your PKT piston was 4mm displaced from where it should be. Wear does not explain this quantum and shaved heads do not explain such amount of travel to my thinking. Not sure what the valve to piston clearance is but given the indentation on the piston crown one imagines it is nothing like close to 4mm.
One would think that the centreline of the crank, the cams, the oil pump and the water pump are all critical to operation and although I am not sure, I might expect that they have to be positioned correctly to within +/- 0.2mm max.
Unless I missed something I have still not seen a credible explanation of why your PKT piston was 4mm displaced from where it should be. Wear does not explain this quantum and shaved heads do not explain such amount of travel to my thinking. Not sure what the valve to piston clearance is but given the indentation on the piston crown one imagines it is nothing like close to 4mm.
One would think that the centreline of the crank, the cams, the oil pump and the water pump are all critical to operation and although I am not sure, I might expect that they have to be positioned correctly to within +/- 0.2mm max.
So what explains the apparent difference of +4mm?
Rgds
Fred
Hi Fred,
It's been a while, but I think his install extension was 9mm, and it was 10mm after the failure event. Now it's back at 9mm.
I think he needs a modification which brings it back to 4-5mm. This is all assuming there are no bent or otherwise damaged parts.
Dave
06-06-2016, 10:00 AM
