Engine overheat and seized - input for next step
11-27-2015, 05:03 PM
#16
Rennlist Member
So, final question - get a full engine / long block or just a short block and machine the old heads? I'm inclined to get a complete engine, the cost difference is pretty negligible. But if someone with some 928 engine building experience could chime in on the likelihood that the old heads could be machined and new valve stem seals installed and call it good, that would be appreciated.
His Black Friday 1/2 price sale on second hand parts is underway and if he has a full motor to suit your MY today is the day or wait until next year unless some other owner can make you a better offer.
Rgds
Fred
11-27-2015, 06:43 PM
#17
Captain Obvious
Super User
Super User
Get a good used engine. The 4.7s are cheap. Then pull the heads and replace the head gasket and other gaskets before putting into the car. I personality don't like to fix severely over heated engines. There could be all kinds of hidden damadge that will surface after you already spent a bunch trying to fix it.
11-27-2015, 07:23 PM
#18
Rennlist
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OK guys, an update. Yes the engine did seize initially. I.E. it could not be turned by hand and the starter would not turn it over. Today I was able to turn the engine over so assuming I was going to need to order an engine anyway - figured I'd try to start it.
It did start and coolant / water was pouring out the exhaust. Leads me to believe what really happened was a massively blown headgasket and hydrolocked engine.
I know a reasonable amount about engines, but really don't want to spend the downtime checking the cylinder walls and block. Since this is mostly my daily driver I'm mostly inclined to swap in a used engine. I can then take my time if I want to inspect this engine thoroughly and possibly rebuild it over time.
So, final question - get a full engine / long block or just a short block and machine the old heads? I'm inclined to get a complete engine, the cost difference is pretty negligible. But if someone with some 928 engine building experience could chime in on the likelihood that the old heads could be machined and new valve stem seals installed and call it good, that would be appreciated.
It did start and coolant / water was pouring out the exhaust. Leads me to believe what really happened was a massively blown headgasket and hydrolocked engine.
I know a reasonable amount about engines, but really don't want to spend the downtime checking the cylinder walls and block. Since this is mostly my daily driver I'm mostly inclined to swap in a used engine. I can then take my time if I want to inspect this engine thoroughly and possibly rebuild it over time.
So, final question - get a full engine / long block or just a short block and machine the old heads? I'm inclined to get a complete engine, the cost difference is pretty negligible. But if someone with some 928 engine building experience could chime in on the likelihood that the old heads could be machined and new valve stem seals installed and call it good, that would be appreciated.
30 years later, that scenario is completely gone. If you are fortunate enough to find a low mileage engine, it's a moot point, because the head gaskets have been sitting in acidic coolant for 15 years or more and are trash.
Used engines, these days, are cores for rebuilding....or if you are really lucky, engines for installing and then selling the car.
To answer your question about your heads, the only way to know if they can be reused is to take them off and analyse the damage.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
11-28-2015, 01:20 PM
#19
Rennlist Member
At this stage of the game, any engine you decide to put in your 928 really needs the heads off and at the very least a completely new gasket/deal set set. This gives you the opportunity to prove there is no corrosion going on. At this stage a perfect opportunity to check the valves and their seating and if you choose to go the whole hog you can do the rings and ultimately the big ends/mains if you have the means to ensure you have the correct tolerance group bearings. Doubtless there will be a good chance the rings/big ends/mains do not need replacement but you really need to establish this as a fact rather than hope for the best.
If the replacement engine has known provenance you can trust so much the better. Once you have a sound engine I think it is fair to say you can rely on what you have for at least another 100k miles and probably much more.
Good luck
Rgds
Fred
If the replacement engine has known provenance you can trust so much the better. Once you have a sound engine I think it is fair to say you can rely on what you have for at least another 100k miles and probably much more.
Good luck
Rgds
Fred
11-28-2015, 07:36 PM
#20
Nordschleife Master
I have to agree with Greg.
I wouldn't drop in a used engine without redoing the headgaskets, inspecting guides etc with a full reseal, it isn't worth it!
I wouldn't drop in a used engine without redoing the headgaskets, inspecting guides etc with a full reseal, it isn't worth it!
11-29-2015, 08:58 PM
#21
Rennlist Member
i would go a step further. just get a cheap used engine , re-ring it, re rod bearing it , regasket it and off you go! take the heads to be looked at by a shop and have them deck the surface or clean it up if they are not warped.
its actually not too hard and on an engine stand , its actually a bit fun! you can have the engine built in a few evenings.
its actually not too hard and on an engine stand , its actually a bit fun! you can have the engine built in a few evenings.
11-29-2015, 10:41 PM
#22
Racer
Join Date: Jan 2009
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If it were me, and I'm in Australia where 928 engines are less available, I'd whip the heads of the engine in the car, find the blown head gasket, check that all pistons still come to the top of the bore, replace the head gaskets and continue on my merry way....
My thinking is, that I would replace the gaskets on any unknown engine that I might buy anyway so I might as well save the purchasing another engine part till another time,if ever.
If you get the heads off and the engine is dead then proceed to the purchasing step.
My thinking is, that I would replace the gaskets on any unknown engine that I might buy anyway so I might as well save the purchasing another engine part till another time,if ever.
If you get the heads off and the engine is dead then proceed to the purchasing step.
11-30-2015, 04:40 PM
#23
Rennlist Member
Thread Starter
I'm a bit spoiled by the Japanese Z car scene. Low mileage 80s era turbo Z engines are pretty cheap and readily available from Japan with a compression test (one in my 88 300Z right now).
RE: 928 International, I have two emails into 928 International and I know one other reputable 928 dismantler I've worked with before I will reach out to. My plan would be to get a full used engine and full gasket set and replace the head gaskets and possibly the rod and main bearings as well unless (by a Christmas miracle) I can find one for sale that has already gone through that process. Thanks for the input everyone.
RE: 928 International, I have two emails into 928 International and I know one other reputable 928 dismantler I've worked with before I will reach out to. My plan would be to get a full used engine and full gasket set and replace the head gaskets and possibly the rod and main bearings as well unless (by a Christmas miracle) I can find one for sale that has already gone through that process. Thanks for the input everyone.
11-30-2015, 07:24 PM
#25
Rennlist Member
but, if its on an engine stand anyway, why not make it new again with new rings. maybe there is no need for the bearings... heck, you might be injecting a little more risk with new ones if the old ones are decent.
11-30-2015, 11:37 PM
#26
Captain Obvious
Super User
Super User
You are not going to make it new by replacing the rings. If the existing ones are sealing well and are already broken in to their bores, what advantage will the new rings have besides the chance or screwing things up and having to deal with breaking in the rings again for no reason what so ever. A leakdown test before pulling the heads will tell if the rigs are good.