A surge of guilt and enthusiasm

[Andy H]

Incentified by Bonzo's enthusiastic start to Porscheness, i decided to get off my butt and get something done with my car.

Im more than fine with all the 'general' service requirements and the other niggly bits I need to do, but decided to remove the timing belt cover last night for a " wee look".
Belts show no major or chronic wear etc, (but im going to change them anyway ), but were very loose ! ,well to me they were ,
Ive read the Porsche manual and used the Autodata from work to print out the procedures, but it states special tensioning tools (which I obviously dont have).
So , my questions are,
1, Confidence in changing them is not a problem, but is it recommended or should I leave it to my garage.(I dont want to destroy a 28k miles engine through lack of knowledge).
2, Not having the tensioning tools, what deflection (if any)should i see in the belts at the measuring points shown for the checks.is this a bad way (old school) to test the belt tensioning or is it acceptable to guage on deflection alone?

New belts are ordered along with the rollers and will be here tomorrow,
Would love to have it done and confidently get to the Sherbrooke meet on Tuesday night, because its not turning another wheel until their done, the horror stories of belt failure have given me the fear !!
Any advice appreciated.

Andy.

 

[barks944]

I've had 3 944's in my family and due to lack of tools and willingness to pay someone else to do it we set ours up using the 90 degree twist method. At the measure point along the long section from the cam pulley to the passenger side balance shaft, when you can just twist the belt 90 degrees it should be OK. You might need to remove a roller iirc. Make sure you don't over tighten it as it will still twist 90 as before but will be too tight. Our current 944's have done about 10k on this method of belt setup and the first one we had went through 2 belt changes change without trouble.

**I am not responsible for the destruction of any engine setup using this method***

 

[TTM]

The balance shaft belt usually seriously stretches after it's been fitted, and this is possibily the reason why the maintenance booklet suggests the belts should be checked 3-4000km after they were replaced.
I replaced the belts last summer and pushed my luck up to 7000 km before checking them, only to find the balance shaft belt very loose - it certainly could have jumped a teeth or two if I had not retightened it.
I personally don't put much faith in the tensioning tool and usually respect the 90 degree twist method on the longest stretch of the balance belt.

Regarding the timing belt I would feel concerned if it indeed feels loose. The tension is applied by the spring tensioner once it's released and it should not move by much if not at all throughout the life of the t-belt. Is the tensioner well tightened on its bracket?

 

[Andy H]

Thanks Tom,
The belts are in my mind hanging off just now (and I gave it a slightly 'spirited ' drive the other day as well ........oops!)
I will ask Owen if he has the tension tools i can borrow, I did ask him to do the job , but he's fully booked for weeks and I cant wait that long.
I did read though to put a feeler guage under the belt and measure between the roller and belt after pushing down approx 1mm,
I'll do it as much to the book as possible and hope I dont muck up somewhere

Never checked anything last night Tom, just noticed how slack the belts looked ,and got the fear, ordered the parts this morning
Andy.

 

[James_G]

I believe that the club has a tensioning tool that it can lend out, although you have to be a member of course. You could try that route.

 

[barks944]

I cant speak for the feeler gauge method, a good option might be to do it yourself initially checking with both 90 degree and feeler gauge and then down the line get someone with a tool to set it more accurately.

 

[rcsalmons]

If you use the 90 deg method on the balance belt it'll sound like a washing machine. This belt should be farely loose.
I've done belts 4 or 5 times now on 944's and have always gone by feel. Especially the cam belt - too tight it'll break, too loose it'll slip.
Just in the process of doing the waterpump and must admit the belts sill worry the hell out of me.

Probably couldnt afford to run the car otherwise.

Rich

PS as I recall the feeler gauge is used for the clearance of an idle roller on the BB not tension so be careful.

 

[Andy H]

Thanks guys,
Im a typical engineer ,, measure twice cut once, (although I do get a bit anal and probably measure 10 times ,just to be sure!),
Just read over the remove /refit procedure again, and I dare say a few times more before I go for it!.
How quiet should the belts be when running?, is there a slight belt noise or are they prone to being a bit more apparent?
Always remember when apprentices done Vauxhall belts to tight, (because they never adjusted them , just stretched them on)used to whirr their brains out.[8|]
Well heres hoping I see a few of you on Tuesday in a 944 rather than the Volvo.

Andy.

 

[TTM]

In my experience belts whine is very inconsistent and as odd as it would appear, doesn't always relates to tension.
I once had a case of a 968 with a seriously whining balance belt that stopped whining after we retightened it without adjusting anything else - perhaps the belt was too loose with regards to how the roller was adjusted and maybe it was the roller that was actually whining.

 

[zcacogp]

My indie only ever uses the 90-degree tightness method ...

The balance belt does appear a little loose when you look at it. That is normal.

Guys - they are belts. Same as on any other car. While I appreciate their criticality for the operation of the engine, I think that people can get a bit over-paranoid about them. Change them, set them correctly and you'll be fine. There is a school of thought that says that the automatic (spring) tensioner is sufficient for setting the tightness without any other means of testing necessary. While I don't subscribe to this, there are people who have done many thousands of miles on cars set up with this method without any problems at all ...


Oli.

 

[Hilux]

Guys - they are belts. Same as on any other car. While I appreciate their criticality for the operation of the engine, I think that people can get a bit over-paranoid about them. Change them, set them correctly and you'll be fine. There is a school of thought that says that the automatic (spring) tensioner is sufficient for setting the tightness without any other means of testing necessary. While I don't subscribe to this, there are people who have done many thousands of miles on cars set up with this method without any problems at all ...

Agree entirely. The only addition I have is that normal belts have relatively short spans between pulleys and tensioners so unless the belt snaps due to age etc or the tensioner fails there will be no issues and it is very unlikely to jump a tooth.

Where its tension is more critical is in engines with longer spans between pulleys/tensioners etc for the lack of tension allows potentially enough slack for it to chatter and bounce off the teeth if not tensioned correctly.

To summarise the 90 degree method is fine but in checking the tension on the longest span on different engines (with different spans) will mean the longer span will have been tensioned tighter. This is less important with sprung or hydraulic tensioners for they apply the tension but is to be considered with fixed tensioners.