Rebuilt top end only or complete overhaul?

[El_Mecanico]

After watching constant smoke out the exhaust I decided to perform a leak down and compression test on a cold engine. The leak down test resulted 2% or 5% depending how you want to read the gages. The compressions were done about a year ago and readings were about 190 psi on all 6 cyl. Finally ready to rebuild my 86 3.2 and the question is should I perform a top end over haul and skip the lower end? The engine has around 115k miles on it. This has to be the cleanest engine I have ever taken apart internally. The out side wasn't bad and oil drips were very minimal. Not enough to show evidence on the floor. Everything points to the valve guides (historically reading) although I don't seem to have a lot of play when moving the valve back and forth. Maybe valve seals all she needed? Is that possible? most of the engines that smoke at idle were due to valve seals. Also my plan was to remove the pistons and cylinders as assembly without separating them disturbing the rings. The liner looks new with no scratches and still the crosshatches visible. Non of the head bolts were broken although I believe the lower ones should be replaced. (historically reading) Back to the original question should I perform a complete overhaul? I have uploaded some pics that may provide some insight. THX

Andy


stalactites in the exhaust port?


combustion chamber


cam shaft housing wear


crosshatch in cylinder liner


valve guide and seat


engine underside

[E Sully]

I would rebuild just the top end. New guides and exhaust valves. If you have Alusil cylinders then your plan to leave as an assembly sounds good. If Nikasil I would put in new rings.
I rebuilt the top end on my 1986 engine with about 70,000 miles due to valve guides. It had Nikasil and I put in new rings. The bottom end did not need to be touched. It came out great and ran like new after break in.

[5String43]

For what it's worth, when the engine in my car was pulled apart last year, it had 148,000 miles on it. The wrench inspected the bottom end and pronounced it perfect. So we did just the top -but that did include new rings, as well as rebuilding the heads. That has worked out very well. Here's hoping the same thing is true of your car's engine.

[Joe Bob]

I've done more than a few tops and never felt the need to split a case unless something is obviously wrong.

Going down low is an unnecessary expense unless you are adding displacement.

[DRACO A5OG]

Hey Dr. M!

So would you be willing to tutor me on a top end re-build some day?

J

[El_Mecanico]

My understanding is the cylinders on a 86 3.2 are Nickies? Would you need to run a honer prior to the ring installation for proper break in?

[Flat6pac]

You want to glaze break before reringing so you can get the oil up in the cylinders but I frown on reringing without doing the bottom end because with the heads done there is too much new on the top and the same old bottom.
Bruce

[gregwils]

You'll find this topic to be like religion. I had to do my motor for heavy oil consumption. BTW, it was like your motor - good compression, low leak down numbers, but loved to drink oil. I ended up doing the top-end, re-ringing and split the case to replace the intermediate bearings.

3.2's' can have niki's or alusil. You need to put a magnet on the cylinder wall - a slight magnetic draw means niki, none means alusil. If you have niki, pull one of the rings off, stick it in the cylinder as it would sit on a piston about two inches down from the top and measure the end gap to see if it's spec. Then you can make an informed decision about re-ringing. Edit: You can break the glaze with soap, water, a GREEN scotch brite pad and elbow grease. Honing the cylinder is way, way, way too rough a finish. Your original hone marks are showing, don't ruin them.

It's more work, but not that much more work to split the case, then you can inspect the mains to confirm the condition and clean all the journals. Bruce says "if the mains are good, then the rods are probably good". There is gobs of info on the Rebuilding Forum and lots of great people to provide guidance. Here was my thread from two years ago.

[El_Mecanico]

THX Greg thats awesome...this is my first Porsche engine drop and I have also armed myself with all the required books as you can see...lol. I just started reading your engine rebuilt and there is plenty of great info...THX for the link. Oh by the way the cylinder liners are magnetic...plus1.

THX Bruce for your advice...I hope I don't get to annoying with posts.

My 86 will be a project car and I'm thinking it will be completed in about a year or so. I will be working on the entire car including suspension and body. The car is in excellent shape but for some reason us Porsche lovers go nuts and are anal about things just got to be right.

I did buy this car from the original owner about 4 years ago...thats one of the reasons why I bought it. I figure when its all said and done this car will be well over 35k...lol. Its funny how so many folks in the forum just don't understand why we do it. This is truly a money pit...lol.



BOOKS!!


Current progress


Before fixing whats not broken

[Joeaksa]

Personally I would not think of pulling the heads off without putting new rings in while you are in there. Same with valve guides and seals. Its just so much work getting to that point that for me I would not think twice about doing both.

[Tippy]

I'll never understand just doing a top end, there isn't much more to doing a whole, full rebuild.

[Porsche Doc]

Do it right! GO ALL IN...

[500_19B]

I am just past the half way point on a 3.2 rebuild (108K miles). After considering various opinions, I decided to split the case. As I am doing the work myself, it really does not add that much more cost in the context of a thorough top end (which, for me, includes new head studs). My intermediate shaft bearings were typically worn, so it was nice to take the opportunity to replace them.

Connecting rod bolts are a popular upgrade on Carrera motors, and that is greatly facilitated when you have the crank out (and for stretch-based tightening, as with ARP, it seems impossible to do those with the case not split...)

[911pcars]

Originally Posted by Tippy

I'll never understand just doing a top end, there isn't much more to doing a whole, full rebuild.

That depends on the definition of a "whole, full rebuild". You have heard about the slippery slope, yes?

In some circles, a full rebuild requires much more work to the crankcase once it comes apart. It can be much more than one would expect and not necessary in many cases.

Sherwood

[porschenut]

The bottom ends on these cars last forever. Doing the "full" rebuild can easily add thousands to the cost if you're paying a shop to do the whole thing. If this were my decision, I would not bother with the bottom end at only 115k, and that's even if I do all the disassembly/assembly myself.

[El_Mecanico]

I did a little research and added the cost to perform a lower case rebuilt resulting aprox 2k. This includes the following;

main bearings
rod bearing
intermediate bearings
chains
cam sprockets
intermediate sprockets
gaskets and seals
misc sealers and lubes
rod conditioning
crank shaft conditioning
chain ramps
race ware rod bolts

Do I need to renew these parts?

Im also planning having the heads reconditioned, new head studs, possibly re ringing the piston. Plus a transmission overhaul, shocks and struts and misc suspension bushings.

Please give me some further advice on the lower case overhaul.

Andy

[TT Oversteer]

Gonna keep it "forever"? I usually over do it then regret it when I sell or move on to the next project.

[schulr]

I too am facing a top end , have just been trying to avoid the cost. Any thoughts on cost for a budget? I am using a qt every 500 to 600 now and having more frequent injector clogging which may be a separate issue. Going to do a fuel treatment with BG 44k and see if that helps.

Bob

[Tippy]

Quote de Tippy

I'll never understand just doing a top end, there isn't much more to doing a whole, full rebuild.

That depends on the definition of a "whole, full rebuild". You have heard about the slippery slope, yes?



In some circles, a full rebuild requires much more work to the crankcase once it comes apart. It can be much more than one would expect and not necessary in many cases.



Sherwood

I can understand the magnesium cases because they require 100% align-boring once split. But an aluminum case rebuild doesn't take long at all.

It only took me like a quarter to a fifth of the total time of the full rebuild to do the low-end.

[911pcars]

Originally Posted by Tippy

I can understand the magnesium cases because they require 100% align-boring once split. But an aluminum case rebuild doesn't take long at all.

It only took me like a quarter to a fifth of the total time of the full rebuild to do the low-end.

About 8 hrs.?

While aluminum crankcases are less problematic than the mag versions, a "rebuild" depends on how much detail you wish to perform.

In your case, did the main and con rod bearings need replacing? If so, how many miles? Did you perform any machining operations (e.g. rebuild con rods, polish crank, re-machine cylinder mount surface, other blue-printing operations, etc.).

Sherwood