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Cam chain and sprocket

Hi All!
I'm into a rebuild of my -71T engine. It will be a stock rebuild without any big upgrades. I have never seen this engine running and have no history of it at all.

Is it default to put in new cam chains and sprockets? If not, how do I determine if I can reuse mine.

Thanks for all input,
Jörgen Forssling
Gothenburg
SWEDEN
Old 06-20-2019, 01:25 AM
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You probably should be more concerned with rust inside the cast iron cylinders
The cam,chain gears should be good if the alignment was kept in tact from any previous opening.
Bruce
Old 06-20-2019, 02:47 AM
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Thanks Bruce,
what should I look for regarding wear on chain and sprocket? I guess the chain gets stretched over time, is it possible to measure if it's within proper margins?

//Jörgen
Old 06-20-2019, 03:13 AM
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The sprocket wear isn't too hard to check, if you have wear and alignment issues you can visually see it on the sides of the teeth. The root of the teeth should be the same thickness as close to the peaks.
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Old 06-20-2019, 05:30 AM
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Normally you keep the gears and replace the chains. They are a wear item and inexpensive.
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Old 06-20-2019, 06:46 AM
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Thanks all!

//Jörgen
Old 06-20-2019, 06:52 AM
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We are seeing issues with "new" cam and intermediate sprockets so if yours are in deed in need of replacement (every engine is different) try to source good used sprockets.
Chain are generally replaced but we see so many rebuilds with new parts and poor assembly that we built a tool to check chain wear.

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Old 06-20-2019, 07:09 AM
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Hi Henry, unfortunately I'm in Europe and cannot use your services. From what I can see, (will get second opinions as well) sprockets and chain looks good. The tensioners firm. Even so, do you recommend me to get new chains? And if so, is it Porsche original chains or any other brands you recommend?

KR
Jörgen
Old 06-20-2019, 11:45 AM
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Absolutely use new chains. IWIS is a branding you will see on the factory chains.
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Old 06-20-2019, 12:59 PM
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If you are going to split the case, it is a no-brainer to replace the chains. You can visually check the sprockets.

Generally, with the motor still together one can estimate the chain wear by judging the distance the tensioner is extended or how much space is left before the idle sprocket tops out or hits the guide.

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Old 06-20-2019, 04:18 PM
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The standard wisdom is to replace chain and sprockets together. That way you can't go wrong. But you can spend more money. And bite off more work, because replacing the intermediate shaft chain gears isn't a snap.

Of course, having a chain actually fail would lead to a minimum of six bent valves immediately, and if lucky up to six broken rockers, with worse to follow otherwise if you kept the engine running (it will run on three cylinders).

But as you can see, that's not the only way guys have done things, and I haven't run across a post where someone said "I wish I had replaced the chain - or the sprockets - or both" when I did the rebuild. Long ago I replaced just the chain when I installed Carrera tensioners. You can replace the chain without removing the engine from the car. I didn't replace any of the gears. When it came time to take that engine apart, all looked fine in the cam drive department.

Misaligned chain gears wear the sides noticeably.

Chain stretch is due to wear on the insides of the links, where you can't see it. The tip about seeing if you have adequate room for the tensioners to work is a good one, which you can also eyeball by how far the tip of the tensioner is extended. But I've not seen any of this quantified - so many mms here or there.

That motor was made rather a long time ago. Do you think that equates to many miles (kilometers) each year, all adding up? Or has it been rebuilt several times, or sat unused for a decade, or something?

Anyway, look at and measure if you still can, those dimensions affected by chain stretch and sprocket wear.
Old 06-20-2019, 04:54 PM
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Oh, and trust Henry to come up with a jig to quantify the length/condition/stretch of a chain. If a guy knew what the dimensions were, it shouldn't be too hard or expensive to make one. The articulating part might be one of the old style, bad idler gear holders we all got rid of to replace with the newer, better ones (though Henry can convert the old to the new).
Old 06-20-2019, 05:15 PM
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Thanks all! I have not seen any indications yet of damage or extensive wear. But we're just started dismantling everything. I'm borrowing the tools to get the cams out soon, so that's what's up next. I will not save money to the extent where i sacrifice peace of mind driving it.

I'll let you know when we're continuing the tear down. The engine is not at home but I have an image of the chain.

All the best,
Jörgen

Old 06-21-2019, 12:58 AM
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That chain looks like it should be replaced.
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Old 06-21-2019, 08:43 AM
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Post up some detailed pictures of the gear teeth, then we can ya or neh them
Old 06-21-2019, 07:57 PM
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Will get back with images when we have the sprockets out.

//Jörgen
Old 06-21-2019, 11:33 PM
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The image you showed makes the gear teeth look not so very good - lots of silver showing on the sides = wear.
Old 06-24-2019, 03:19 PM
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Excellent thread. Thanks for sharing your wisdom guys. Answered several of my nagging questions.

Henry
Old 07-21-2019, 10:42 AM
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Look at the antique second generation chain rails...
Bruce
Old 07-21-2019, 11:47 AM
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Quote:
Originally Posted by Flat6pac View Post
Look at the antique second generation chain rails...
Bruce
Could they be original to a 71 engine?

//Jörgen
Old 07-21-2019, 10:55 PM
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