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RickF
Joined: 03 Aug 2015 Posts: 44 Location: Howell, NJ 07731
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Posted: Tue Dec 08, 2015 9:40 am Post subject: 924S Engine Rebuild or Replace? |
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The timing belt let go on my 87' 924S. It occurred at idle with clutch disengaged. I know I have at least a couple of bent valves but not sure of piston damage yet. I'm pulling the head to inspect everything. My question to the Forum is, "At what point should I decide that it's more prudent to just replace the whole engine or completely overhaul the one I have?" I would really appreciate all help, input, experiences and expertise of this group before I proceed.
Thanks for your help. _________________ Rick |
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fiat22turbo
Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR
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Posted: Tue Dec 08, 2015 9:54 am Post subject: |
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A head rebuild isn't too bad.
Not sure why you'd need to replace the engine for that, especially since they are known for going to 200-300k with proper maintenance. _________________ Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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RickF
Joined: 03 Aug 2015 Posts: 44 Location: Howell, NJ 07731
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Posted: Tue Dec 08, 2015 10:05 am Post subject: |
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I'd have no problem rebuilding the head if bent valves and damaged guides are the extent of the of the damage. However, if the pistons are damaged or holed then wouldn't that necessitate splitting the cases? I ask as this would be the first time I've worked on a water cooled Porsche. _________________ Rick |
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Fifty50Plus
Joined: 28 Feb 2008 Posts: 1353 Location: Washington DC area
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Posted: Tue Dec 08, 2015 10:12 am Post subject: |
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Most likely the pistons aren't damaged at all as long as it didn't occur at 6000 RPM. I just did one and you can barely tell that the valves tapped the piston top. _________________ 1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car |
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RickF
Joined: 03 Aug 2015 Posts: 44 Location: Howell, NJ 07731
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Posted: Tue Dec 08, 2015 1:15 pm Post subject: |
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I can only hope there is little or no damage to the pistons. The car was well maintained so I have my fingers crossed. _________________ Rick |
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jason c
Joined: 13 Jan 2014 Posts: 1018 Location: Nwi
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Posted: Tue Dec 08, 2015 2:23 pm Post subject: |
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Fifty50Plus wrote: | Most likely the pistons aren't damaged at all as long as it didn't occur at 6000 RPM. I just did one and you can barely tell that the valves tapped the piston top. |
I agree. Busted pistons are rare in the 2.5 with a broken belt. Very unlikely at idle.
Just have the head redone with new valves & let it roll.
Bet you won't skip another timing belt service. |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Tue Dec 08, 2015 11:33 pm Post subject: |
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If you have time on your hands (winter project) and your are committed to the car, I'd recommend pulling the motor to: 1) do the belt service, 2) inspect the clutch, 3) replace rod bearings, and; 4) reseal the engine. Also a great opportunity to work on the wiring harness. _________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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RickF
Joined: 03 Aug 2015 Posts: 44 Location: Howell, NJ 07731
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Posted: Wed Dec 09, 2015 12:13 am Post subject: |
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Good News! No damage to the pistons! Couple of bent valves, etc. So, I'll do a complete head overhaul and service to the cam, etc. I was rather surprised the timing belt let go as it only had about 20k miles on it and it was about 4 years old. I'm thinking the belt was old when installed by to PO. Just as an afterthought, is there available a timing belt to chain conversion? I haven't researched it yet but in light of the inherent problems this engine has with timing belts I would think a timing chain setup would be more sturdy, longer lasting and more desirable. _________________ Rick |
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jason c
Joined: 13 Jan 2014 Posts: 1018 Location: Nwi
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Posted: Wed Dec 09, 2015 10:20 am Post subject: |
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RickF wrote: | Good News! No damage to the pistons! Couple of bent valves, etc. So, I'll do a complete head overhaul and service to the cam, etc. I was rather surprised the timing belt let go as it only had about 20k miles on it and it was about 4 years old. I'm thinking the belt was old when installed by to PO. Just as an afterthought, is there available a timing belt to chain conversion? I haven't researched it yet but in light of the inherent problems this engine has with timing belts I would think a timing chain setup would be more sturdy, longer lasting and more desirable. |
Age of the belt is as big of a factor as mileage. Iirc, the factory recommended interval is 2 years or 30k miles.
The timing belt design isn't the issue, the owners lack of maintenance is. In 20+ years of owning these cars (I have owned several at any given time), I've never lost a belt. Maintenance is key.
Timing chains need to be encapsulated in covers within the crankcase so they are constantly lubricated, this is not possible on these engines without a significant design change. An unlubricated chain is a disaster waiting to happen. |
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fiat22turbo
Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR
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Posted: Wed Dec 09, 2015 11:14 am Post subject: |
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Porsche did screw the pooch with the timing belt design to some extent given the number of similarly sized engine from the same time period that utilized timing belts without similar issues.
That said, proper maintenance is key and they'll last a good long time. More importantly, drive the damned cars, sitting doesn't do these cars any good. _________________ Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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RickF
Joined: 03 Aug 2015 Posts: 44 Location: Howell, NJ 07731
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Posted: Fri Dec 11, 2015 10:39 am Post subject: |
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With the head removed a close inspection of the head gasket and the crankcase surfaces revealed some clogging of the galleys for the engine coolant between the two. I've seen that before on motors that have been sitting a while without the coolant being drained. Stefan, you are 100% correct.... sitting really doesn't do these cars any good! Thanks all for the help and insight. _________________ Rick |
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