Getting my 86' on the road

[jwerks]

After years of wanting one, I finally own a 944. I came into ownership of this car through a trade. The previous owner gave me a list of work he had completed which included a new clutch and brakes all around. The only down side at the time was that the car smoked excessively and the PO believed it to be a head gasket. Easy enough right?






Initially when looking at the car, I had found what I thought was a magic bullet. The PO in attempting to fix the poor idle/misfires/smoke had installed a rebuilt early DME. Changing the DME to a late one (which matched the AFM) and replacing the DME temp sensor completely changed how the car ran as well as the smoking which basically disappeared after a few heat cycles. With this turn of events, I decided to address some other issues since I felt the car would be on the road in no time.

I first started with making a new vent tube for the steering rack. Someone had installed a soft hose (I'm guessing fuel hose) and it swelled/leaked. Hopefully this hose here will work for awhile.





Then I decided to get the drivers door refreshed. I lubricated the regulator tracks and disassembled/cleaned/reassembled the window motor. After that, the drivers window worked fairly well. I haven't done the passenger side yet so I'll be sure to document that side better.



Next I ordered a dash mat and some floor mats. After a nice vacuum and re-gluing the edges of the carpet, the interior cleaned up pretty well. I also sewed on a new shift knob since then.



After finally getting some work done on my other project, I was able to get the 944 in the garage. I had decided that I was going to go ahead and replace the head gasket for piece of mind and reseal the balance shafts. What I found kinda sucks...







This is cylinder 4. I found a small piece of metal broken off at the top of the piston. Im speculating that the timing was so out of whack with the previous DME installed and the PO trying to drive it that it detonated on this cylinder. SO, I am evaluating my options on how to go about this. In the mean time though there are plenty of other tasks that need to be addressed so I will update as I go along.

-Cheers

[Monkey Wrench]

my guess is that a tiny fragment of piston ring , or perhaps a bit f the valve was trapped in the cylinder and knocking up and down between the head and the top of the piston. you may see some marks like that on the underside of the head

Ive seen similar where a bit of ring came up into the area. I've even noted a sound of " rattling noises preceeded by pssst psst psst, and then Pting ! "
that's the sound of a bit of compression ring stuck between hitting the top of the piston and the head, then preventing a valve from closing and then finally exiting through the exhaust pipe .

Id look at the bore in the area, look for any vertical scraping there. I don't know if you actually have ring damage. the marks could have been from a bit of a valve, were the valves missing any fragments?

i dont want to prompt you to remove the pistons if the engine can be used without such disassembly. Id ask others for their advice on that, but see if that bore is scored up, that may show more. it doesn't appear in this case that there is much of a hole there but maybe there is enough to cause issues. you dont want a broken compression ring, it'll burn oil.

if you do replace the rings, be careful not to break them , there is tool for that that doesn't look like a hose clamp. using a hose clamp is basically a farmer's trick.

i once broke a compression ring and I could not buy one ring, I needed to buy a whole set.

you are right this does look unfortunate, you do have a scored bore there and you may or may not have a broken piston ring that is exiting in fragments. It probably means a new piston from my view, but ask the others too. removing the piston is obviously more than you bargained for or deserve .

sorry to see this but now how far do you take it? rebore? recoating ? new pistons? balance the new pistons rods, crank etc? different block? you might have choices. some may depend how deep your pockets are.

with most engines you could buy new pistons, rebore and you are on your way but I dont think you can simply do that because of the special coating which could be expensive, and I'm unsure if you can just put oversize pistons in.

If you want to go all in I'd have the parts balanced professionally then at redline it will sound better, but that may be way further than you wish for. I would say though, that when I did it in my old volvo the cost of such accurate balancing wasn't really a show stopper. it was maybe $300 or so. crank pistons , rods , flywheel , they balance the rods against each other and the two ends of the rods also the whole unit crank , flywhhel etc. even the brand new pistons had some material removed to improve balance.
I think it made a huge difference and it wasn't thousands of dollars. I dont know what extent Porsche goes to, likely higher tolerances than an old volvo.. it may be quantified.

i'd look into it if you go that far, see what the cost really is. a truly balanced engine can really sing and sound beautiful at its redline. manufacturers work within certain thresholds so when you hear of an engine being balaced and blueprinted , it means they did the balancing and also checked every other spec to get it within its tolerance. factory tolerances can be exceeded.

even if you DYI you can weigh the pistons and make them all the same weight. probably the ports are not very rough in a porsche but on a lot of engines polishing the ports can also improve the flow and performance thus more HP, without changing displacement.. you can go further and CC , make each piston equal in displacement. perhaps even tune the flow. then you are into racing stuff I guess..

then do you have a head shop do a proper three angle grind, can they replace the valve seats? or would you just lap the valves by hand and reasssemble. depends on what you can afford.. new guides? knurl the guides to reduce the ID and then ream them to fit the stems?

if you plan to flip the car then well you may not want to spend lots.

I dont think the objective was perfection you just wanted to make it good enough to run right and use it or flip it maybe.. I'm sure if you got the advice of one of the racers they will have a lot more very valuable knowledge and experience on all this stuff.

on some engines the factory did not do a very precision job of mating the ports , like between the manifold and the head. you could notice some step in the alignment of the gasket on either side, sometimes you can remove a bit of material and that can improve flow, you can use a new gasket to try to compare and look for any step that may impede flow.

my guess is that its more precision than some other engines because its a porsche.

Porsche saved weight by using an aluminum block but there are some obvious issues when it comes to reboring them.

maybe with a new piston you could do a re-ring and run it with the little scoring there and not have a huge problem? my take is you need a piston but I'd ask the others, dont go by just my opinions. my guess is that your compression ring is leaving up through the top near the edge, and you can't ignore that or it will haunt you . If that's true it does suck.

[djnolan]

Since you already have the head off replacing rod bearings is a common repair for these engines. This would allow you to replace that piston. Might also do the valve guide seals. These engines can go 250k without rebuild. How many miles are on it? You could source a used piston in the parts classified forum. I would get expert advice regarding the scratch in the bore first and rule out a valve problem.

[Monkey Wrench]

can he drop the pan to remove the rod or does it require complete engine removal?

[wwdwgs]

MW,
the oil pan can be dropped after the crossmember is removed and that will mean - to remove steering rack, lower control arms, sway bar, stabilizer link(s)...maybe, something else. The the front wheel alignment has to be done.
Perhaps, it's less work then removing an engine.

[Monkey Wrench]

im wondering if the headgasket was actually bad or maybe its only a piston ring issue.. causing the smoke .. in other words the head may be ok. was there water coming out the exhaust?

he said the clutch was done.. I'd look locally and see if there might be another car that could provide the parts, or maybe someone has a shortblock without the scoring issue.

the way i see it yeas he could find a used piston ,put new rings, bearings too? but with all that work and expense. leaving a scored up bore?

it becomes a big economic decision I guess. I don't see a cheap way out
Even a used engine is a gamble. maybe a 944 that became an accident victim could be a better bet. cars with good engines do get written off due to accident damage.

[djnolan]

Originally Posted by wwdwgs

MW,
the oil pan can be dropped after the crossmember is removed and that will mean - to remove steering rack, lower control arms, sway bar, stabilizer link(s)...maybe, something else. The the front wheel alignment has to be done.
Perhaps, it's less work then removing an engine.

I have heard or read about a way to do this by lowering the cross member by turning the bolts almost all of the way out but not needing to actually remove it to get clearance to remove the pan.

however if it also needs a clutch maybe pull the engine out the top and do a complete reseal, bearings and repair of the bad piston.

There are many posts on this forum about scoured blocks, rod bearings, and various techniques to pull the engine, pull the pan, replace the clutch, etc.

Search the forum for ALUSIL, the compound the block is made from...

Regarding the scoured block i recommend starting a separate thread with a more catchy subject and post those pictures.

Also check out this thread: Cylinder walls-Scoring