Uhh-Ohh…., My Ongoing 914 Build Adventures.... Options

[porschetub]

Check with Clewitt about the crankfire pulley,hopefully it isn't different,I used the 10 x 710 and no issues for a short time till it started making noise,not slipping just a PITA noise turned out I had worn pulley faces,ordered a new outer and hope that fixes it otherwise I will get my fan hub machined.
Be careful to set the belt tension right as the bearings in these altenators are fairly small and you don't want to strain the magnesium outer housing as I did and the fan blades rubbed.
Getting close Lawrence (IMG:style_emoticons/default/aktion035.gif) .

[SixerJ]

9.5x710 or 10x710 should be correct. Did you move any shims between the pulley halves yet?

(IMG:style_emoticons/default/agree.gif)

Great progress! Fairly sure my 2.4 engine has or rather had 3 or 4 shims (have to admit I haven't done the last 2 services / alternator had to be replaced in that time frame)

I do clearly remember the 1st time I did the belt, and it's amazing how much of a difference even adding or removing a single shim makes. I had to go out and buy some more the 1st time I did this job and also keep some in a packet tucked into the tool kit

[McMark]

Just run a tape measure around the pulleys. 710 is 710mm is 28". The PET specifies 725 for 76-79 911. That might be your target. But I'd just measure it and round down since the belt sits down in the upper pulley, you're measurement would be the MAX size, not the ideal size.

[Larmo63]

Or, I look for a 82mm pulley half.....?

[mepstein]

9.5x710 or 10x710 should be correct. Did you move any shims between the pulley halves yet?

(IMG:style_emoticons/default/agree.gif)

Great progress! Fairly sure my 2.4 engine has or rather had 3 or 4 shims (have to admit I haven't done the last 2 services / alternator had to be replaced in that time frame)

I do clearly remember the 1st time I did the belt, and it's amazing how much of a difference even adding or removing a single shim makes. I had to go out and buy some more the 1st time I did this job and also keep some in a packet tucked into the tool kit

The pulley should have 6 shims. Adjustment is just moving the shims in front or between the pulley halves but never removing them completely.

[Larmo63]

Yes, all shims are present and accounted for.

[McMark]

Or, I look for a 82mm pulley half.....?

Sure... but you can head down to your FLAPS and get a belt today.

There is something about pulley sizes, ratios, and rotational speed. But I don't feel like looking all that up. (IMG:style_emoticons/default/tongue.gif)

[Larmo63]

I believe that a larger pulley turns slower.....?

[euro911]

Which did you change (go larger with)? ... Crank pulley or alternator pulley?

[Larmo63]

10 x 725 belt fits perfect......

[euro911]

(IMG:style_emoticons/default/thumb3d.gif) ... then you'll have it up and running this w/e? (IMG:style_emoticons/default/driving.gif)

[porschetub]

9.5x710 or 10x710 should be correct. Did you move any shims between the pulley halves yet?

(IMG:style_emoticons/default/agree.gif)

Great progress! Fairly sure my 2.4 engine has or rather had 3 or 4 shims (have to admit I haven't done the last 2 services / alternator had to be replaced in that time frame)

I do clearly remember the 1st time I did the belt, and it's amazing how much of a difference even adding or removing a single shim makes. I had to go out and buy some more the 1st time I did this job and also keep some in a packet tucked into the tool kit

The pulley should have 6 shims. Adjustment is just moving the shims in front or between the pulley halves but never removing them completely.

Six shims,not for the early motors 2 to 3 as far as I know but this a later motor so that may explain it?

[porschetub]

10 x 725 belt fits perfect......

Not sure, looks very low in the top pulley,perhaps a few less shims,the belt should be level with the top of the pulley halves or there abouts,try that.
It needs to sit as your crank pulley or a little under.allowing for initial belt stretch.
When its right you will have a really small deflection,around 10-12mm cause its a short belt,otherwise you may need something slightly longer if it appears too tight.

[McMark]

Not sure, looks very low in the top pulley,perhaps a few less shims,the belt should be level with the top of the pulley halves,try that.
It needs to sit like your crank pulley.

If it's tensioned correctly, why would you care how low it sits in the upper pulley?

The whole shim-based tensioning scheme pretty much guarantees the belt won't sit like the bottom pulley. If they wanted it to sit at the top every time the shim setup is a bad choice and a std pulley with tensioner would more effectively accomplish that.

And... the higher the belt sits in the fan pulley, the longer the belt is. The belt sitting at the very top means that's the longest belt possible. And that means that if the belt stretches a bit over time, you have no more room for adjustment.

I think the right, or better, answer to 'Where should be belt ride?' is... Anywhere, as long as:
1. The belt is tensioned correctly.
2. The belt sides are fully contacting the pulley walls.

[porschetub]

Way I was taught,have edited my reply ok Mark.

[Larmo63]

The belt deflection is close to 10mm in this set up.

I'm happy with it.

Engine goes in tomorrow.

[Larmo63]

The belt has room to break in and stretch + the shims can come out.

[Larmo63]

By the way, when we had the heads off, we measured the pistons and they are 84mm. That means this engine is really a 2.4. We think the cams will give us milder "S" type performance numbers, along with the porting work we just did.

Oh, and also by the way, I was told the engine was built to a 2.7 spec and I bought it as such................ Oh well.

I think it will be a fun car, nonetheless.

[Krieger]

(IMG:style_emoticons/default/piratenanner.gif) Dude, your almost there!

[porschetub]

By the way, when we had the heads off, we measured the pistons and they are 84mm. That means this engine is really a 2.4. We think the cams will give us milder "S" type performance numbers, along with the porting work we just did.

Oh, and also by the way, I was told the engine was built to a 2.7 spec and I bought it as such................ Oh well.

I think it will be a fun car, nonetheless.

What the hell ,it will still go really well with that combo,nothing wrong with what you have,you should make 160-180hp easy (IMG:style_emoticons/default/aktion035.gif) (IMG:style_emoticons/default/aktion035.gif) .