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Joined: 07 Nov 2016
Posts: 25
Location: Pembrokeshire

PostPosted: Fri Jan 06, 2017 7:54 am    Post subject: SC Engine rebuild queries Reply with quote

Morning Guys

I have had a garage look at my 911 sc engine just before Christmas to check it over. Engine is out of car and has been there a few weeks. I had just bought the car as a project.
Prior to the car being stripped for bodywork, the car was driven onto a trailer and the engine ran perfectly (I have videos of this), no smoke, maybe sounded a tiny bit tappety.
I have heard back off the place that has the engine and apparently all 12 valves have had it and need replacing and it needs a top end rebuild at a cost of around £8k.
I was really surprised at this as the engine sounded so sweet. So I have gone through the extensive file that came with the car and discovered that the engine had been out of the car less than 10,000 miles ago and had seals replaced (this was about 6 years ago). It also following this had a full rolling road dyno which I have the print out for showing 181 BHP. As this is a 1980 model, this is only 7bhp down on new.
Is it possible that this engine could have deteriorated this much in less than 10,000 miles? Unfortunately, without my go ahead the garage has gone ahead and changed all the valves......
Any thoughts? Could anyone tell from the video(s) of the car running whether all the valves were that bad? I do have close ups of the exhaust while the car is running showing zero smoke.
Any opinions appreciated. I'm not a mechanic, but these added costs could really give me issues in finishing the project.
2015 Macan S Diesel
1995 Carrera 2 993
1979 911SC (currently being backdated/ renovated)

Previous Porsches now sold:
2003 996 C2
2000 Boxster 2.7
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Joined: 29 Oct 2016
Posts: 19

PostPosted: Sun Jan 08, 2017 5:44 pm    Post subject: Reply with quote

If the car wasn't smoking at all when warm I doubt the valves were bad. Unless you were using more than normal oil and the power was down?

Why did they remove the engine? Did you authorise them to do this?

If you didn't it sounds dodgy to me. Which company was this?

I have heard of the valves bending from miss shifts but not on these engines from normal use. Although if it was sounding like loud noises from the tappets it could be that the valves haven't been adjusted for a while and that the clearances were wrong. But I'm no expert at all just enthusiastic hobbyist.

I have a Mercedes e class AMG and that hasn't been on the road for 7 years and not started for a while, recently got it started and that sounds tappety but has hydraulic lifters so I know it's just due to the engine been standing for a long period. This should fix it self with an oil change and more use. Engine is otherwise fine definetly no need for new valves.
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Joined: 01 Nov 2015
Posts: 2495

PostPosted: Sun Jan 08, 2017 6:06 pm    Post subject: Reply with quote

the only precise way to see the extent of engine wear is to open it up, did you authorise an engine removal?

if it was running sweet, then in my book, that means it was o.k.

mine has 127k, has never been opened, smokes on initial start up, which is normal, burns no oil and goes like the clappers.

So according to a specialist, mine needs a full rebuild urgently? no of course it doesn't.
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Joined: 19 Jan 2014
Posts: 115
Location: Prestwick

PostPosted: Wed Jan 11, 2017 9:33 pm    Post subject: Reply with quote

Personally I'd get them to put the engine back in the car, get it serviced, adjust the valve clearances then get a leak down test done....... By another garage, or it's not a difficult job to do yourself if you know how. It's normal for these engines to sound a bit tappety if they haven't had the clearances set for a while.

A full top end rebuild on an engine which was running well and didn't smoke should not be necessary, unless the compression is way down.

I'd be interested to know how they think the valves are needing replaced when they haven't stripped it down? Normally that's something you discover when you've taken it apart.
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Joined: 21 Mar 2015
Posts: 7848
Location: Brighton

PostPosted: Thu Jan 12, 2017 7:56 pm    Post subject: Reply with quote

The valves are there to allow the air/fuel mixture to enter the cyliders , then hold compression and finally to allow the burnt gasses to escape .

To test you would do a compression check and a cylinder leak down test.

These old girls do tend to need to be at operateing temp for an accurate compression test .. they are not young any more !

Depending on the results obtained is whether further investigation is needed .

For oil smoke then piston rings or valve guides / seals would be the most obvious .

I assume they have stripped the heads and found the valve guides to have excessive play , the stems of the valves can also wear so you would tend to replace both .

The valves can burn out causeing low compression and the valve seats can wear causeing the same , a missfire would tend to be obvious if only when cold in that instance .

An inspection of the old valves might be useful in alleviating or confirming your concerns .

It is customary though to obtain permission before any work is carryed out .
My Daughter's Crowdfunding has hit the target .

Thank you all so Very much .

She's not going until july 2020 though .


7pm - 9pm

Indy Mechanic .
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