Top End or Complete Rebuild?
 

Hi All,

I stripped my '78 911 SC engine down to the short block. At least 85K on the car.. could be a lot more as speedo was replaced by PO. Keep in mind this is the very first engine I have stripped down, so my experience is minimal. I am debating whether I should stop at a top end or do a complete rebuild. Here's why:
*Oil pressure: 4-5 bar when cold. Then, when warm, will match the revs up to 3 bar. It maxes out at 3 bar regardless of higher RPMs. I did not check the pressure sender nor do a mechanical pressure test before pulling the engine. I checked the connecting rods and all look good. Some side-to-side play (which I read is normal) but no back and forth play. Cylinder 5 rod has some pitting on the rod where the piston wrist pin goes through. See photo.
*Knocking Noise: Seemed to be coming from cylinder 4, 5, or 6 valve train but I don't want to assume. My cam rocker shafts were beginning to walk out on the exhaust side. If it is a rod knock, would it be obvious upon inspection of the rods in the short block?
*Compression/Leakdown: 110-120 PSI on all cylinders (consistent). 75% leak on cyl. 1 (intake) and 5 (exhaust). 20% on 6 and 2 (rings). 4 and 3 had good leakdown numbers. Guessing this will be solved by the top end valve job and new rings.
*Chain: Looks good but has obvious wear/darker spots.

What would you do? Top end or full rebuild? Note: this is going to be a street car and not a track car.

Supporting photos:

Pitting on cylinder 5 connecting rod (where wrist pin sits). This is the only rod that has pitting:
http://forums.pelicanparts.com/uploa...1710740933.jpg
Rods on cylinder 4, 5 and 6 end: notice the gunk especially on #4 opening.
http://forums.pelicanparts.com/uploa...1710740954.jpg
1, 2, 3 side of the case. Notice how the case openings on #1 and #2 are a lot darker than #3. Is this a problem? What is the cause?
http://forums.pelicanparts.com/uploa...1710740971.jpg
Timing chain showing wear:
http://forums.pelicanparts.com/uploa...1710741000.jpg
Pistons and cylinder heads. 1,2,3 on the left and 4,5,6 on the right.
http://forums.pelicanparts.com/uploa...1710741017.jpg
Image showing carbon buildup on the piston. All pistons & rings seem to have a lot of carbon buildup.
http://forums.pelicanparts.com/uploa...1710741053.jpg

One thing you could do is check the big ends - split the bearing halves and plastigauge and visually inspect the big end bearings. You can do this without splitting the case.
The warm oil pressure pegging at 3 bar is a bit of a clue. A fresher bottom end will be higher.
It is probably nicely worn but not beaten up.
Alan

Same comment as Alan: Check the rod bearings either by measuring or by Plastigage. If they are good, the main bearings and crank almost certainly are good too. If you want to split the case, that will add several thousand dollars to your bill.

Darker color comes from longer intervals between oil changes , too long , way too long .
5,000 is just fine with Driven GP1. 11+ quarts , change your oil if it gets over 235-245 degrees , heat will change the color of the aluminum as well , dirty brown color .
The way your engine looks I would split the case , no big deal just take your time .
You have the best series of engines , 78 big port heads and the most simple CIS.
Put some M1 - Kermit cams it and it will go like stink.
AASE valve springs and Ti retainers , when you are done make sure you rev the ***** out of it
7,000 rpm every day at least 30-300 times , have fun with it .
Ian

Yes - I suspect the engine has had a lot more than 85k on it. And that oil pressure - while 'acceptable' is not what you would be looking for in an engine that has just had a refresh. It is only downhill from there. And less than 3 bar really would be unacceptable for even a medium term proposition. The bottom end will tell the final story.
Alan

We’ve never opened up an engine and thought it a mistake.

Full rebuild. 100%. No question. Replace, chains, guides, check sprockets for wear. Enjoy the process.

If you only do the top, you will always be thinking "I wish I had done the whole thing".

Thanks for the input. What are the biggest cost adders on the bottom end? I assume a replacement oil pump and IMS shaft are the big ones (there's $2k right there). I spoke to Walt at Competition Engineering this morning. He didn't think the 3 bar max was the end of the world, but he also did not see pictures of my case that I posted here.

What is the key cause of the oil pressure issue? I would assume lack of pressure being supplied by the pump is the main culprit on a "tired" engine?

Unfortunately, it ran a bit hot the last few times I drove it (upper white mark on gauge ~245 F). When it got to this point, I turned it off and let it cool down. Turns out that rodents made a large nest right on top of the oil cooler.

Ian, thanks for your suggestion. I sent William an e-mail asking for more info about these cams you mention.

Not sure about the pump being the issue. Wear in the crank and bearings. Machining and new bearings, and big end shells etc etc.
Alan

Gotcha, thanks Alan.

Just came back in from removing lower Dilavar head studs. Some came out with little effort and others required a lot of force. They're all out now minus two snapped ones on cyl. 1 & 2 that I have to remove the case nuts in order to slide my stud removal tool onto. That's for tomorrow night...

When I peeked into cylinder #6 again, I noticed this. WTF.. looks like a lobe off the crankshaft has broken off! :eek: This certainly isn't normal, is it?

http://forums.pelicanparts.com/uploa...1710831755.jpg

That does look a bit odd. You may find something in there :-)
Heat is your friend to get broken studs out. More the better. Normal propane gas is barely sufficient.
I use oxy and propane/butane. used to be acetylene. Don't break the short bit of the remaining studs - or you really will have problems. Use heat if they won't come. If they still aren't coming - more heat. They should come free easily if you have enough heat.
Alan

Like Alan said about the heat, really lay it onto the area around the stud and the inner register wall. Don’t be shy.

Yeah that crank web doesn't look right. I retract my earlier advice. You now have a good reason to split the case.

However, as you do, keep the bearing shells in order so that you can reuse them if they are good. Reuse bearings? Yes. journal bearings do not wear out in normal use. They wear out because of lack of oil or contamination. Measure and plasitage--if they are good, reuse them. That will save you $600 or so. Same for the rod big ends.

Your oil pressure is below factory specs. Why even consider a top end only build?

Cheers

I’ve decided to split the case after hearing your input and wanting to do this the right way. The kiddos slept early tonight so I got a good 3 hours in the garage. Got the hard oil pipe off (thanks pipe wrench), removed the 2 broken studs, and got most of the case bolts undone. Only a handful left. Will be splitting tomorrow or the next day. Gotta say those case bolts smelled very funky (kind of like formaldehyde).

The steel studs on the intake end appear ok. I recall Wayne mentioning that they can be left in the case. I may just do that unless you guys have heard of those snapping?

On another note, the Ultrasonic Cleaning shop tested my engine oil cooler and oil tank today. Both are leakers. External oil tank wouldn’t hold 2psi and oil cooler started leaking out at 10psi. Maybe that’s part of my pressure issue. Will keep you all posted on the progress.

Good work and likely a good decision. You will feel better when you put it all together with a fresh bottom end as well.
not too likely the cooler is the cause of low pressure. You would have to be loosing quite a lot of oil. You already have a loss system with the piston squirters and cam spray bars. You would need to be loosing more than those to make a difference. I suspect you will find the answers in the bottom.
Alan

Low oil pressure at rpm when hot can be an indication of excessive bearing clearance. Not just the rod big ends, but also the crank main bearings in the case. When the case is apart, measure your bore accurately.
I had a motor with simlar oil pressure and the main journals all measured between 3.5 and 4.5 thou. Those 7 sets of journal bearings on the large side, are like having 7 little oil leaks...

Mike speaks wise words.

The tank sees almost zero pressure..... Was it leaking? If not, testing it is a bit of a waste.

Did your oil cooler leak?? If not, it holds pressure. Maybe find a place to test it that knows a little bit more about what they are doing.

Cheers

Mike and Alan, thanks for the input.

Jeff, one of the shop’s specialties is testing oil coolers. While the oil cooler wasn’t actively dripping, the area certainly was covered in oil. I’ll stay on the safe side and try to source one in better condition. The oil tank’s leak was from the welded mount bracket area. Agreed that it doesn’t hold much pressure but it is still an entry point for oxygen. I’m talking to a couple of shops that may be able to braze/weld it.

Well I decided to pull all the steel head studs on the top of the case tonight. I just wasn’t comfortable leaving those on due to the age and the small amount of surface rust. A couple of them took a propane torch, but they’re all off. Got those handful of nuts off and now all the fasteners are off the case. Going to call it a night and get to case splitting first thing tomorrow evening.

I know the nasty smell from the case bolts. A very unique smell. I thought rotten eggs.

That crank looks troublesome could be the source of your knock and low oil pressure if that piece is in the bottom of your case.

That certainly could be, however I didn’t see any pieces floating around and never remember seeing any come out with past oil changes.

Got everything disassembled over the last week. I’m starting to clean everything up. Going to drive the case, cam towers, Ps & Cs, crank, and rods over to Ollies in Lake Havasu next week. I was able to schedule some customer visits for work in Vegas which makes the trip worth it. Heads are going to Aasco Motorsports for reconditioning and a valve job. Finally, the cams are going to Dougherty for a regrind.

Excited to see this coming along but now it’s just a waiting game for the machine work to be done. Will keep you all posted.

While beginning to inspect my fuel lines in the chasis I did run across this crack in the frame :-( http://forums.pelicanparts.com/uploa...1711725395.jpg
http://forums.pelicanparts.com/uploa...1711725395.jpg

Probably from the hit and run accident I had a few years ago when someone hit that side of the car when I was parked on the street. Time to find a portable welder that can come to the house and fix it.

What was the result of the oil cooler pressure test? Did it pass or fail? Or did I just miss it (likely) :) ....

You should have not problem finding a shop to braze the oil tank. Keep us posted on that end of the work.

You have made some good choices on the outsourcing work you posted.

Looking forward to progress updates as your build continues.

Koodos to you and those that take this on!

Cheers

Thanks Jeff! Appreciate the help and input you’re providing. It’s a big help.

The oil cooler was a leaker. Lots of little air bubbles at 10psi. I asked Tim at Ollies for a second opinion as he also tests them. He told me that he recommends replacing if they begin leaking at 40psi. I have dibs out on a used cooler that I’m hoping to have tested but I’m also considering biting the bullet and just getting a new one. After all, the engine is almost 50 years old. While at Ollies, Glen Yee from Glen Yee Motorsports will be looking over my oil pump. He’s close with Tim at Ollies.

Regarding the oil tank, I had it shipped to Orozco’s Gas Tank Repair in Bellflower, CA. For $190, they welded the bracket. I’m also asking them to straighten out the outfeed tube on the tank since it’s not perfectly round which causes some seepage.Hope to get it back early next week.

I’ll keep you all posted. It will be 3-4 months till I get my engine back. I was impressed with Tim and the crew at Ollies but they certainly have a lot of engines to work on before they get to mine. Next step is to pull the gas tank and refresh the fuel lines. Then, take care of the crack in the frame and install my new wiring harness that I should be getting soon from Restoration Design :-)

Re the crack in the weld at the left front lower corner of the engine bay: I doubt that was from one impact. It looks more like a stress crack or fatigue crack to me. If someone had really stiff shocks on it at some point, and did off-road rallies, that might be the result. If that's the only place, then weld it up. But after seeing that, I would inspect much more closely around the other corner and the upper shock mounts, because that stress came from somewhere.

Crank lobe looks to me like it was drilled for balancing purposes and they might have knocked the corner off while doing so.

Do you know what viscosity your oil was, giving that oil pressure?

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Oh hang on you mean the other lobe!

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Pete - I inspected the other side but did not see any cracking. The car is a salvage title, so perhaps it could have happened long before. I'll do more inspection after I get back from vacation. The other issue I'm trying to figure out is why I have a 10mm door gap on the driver's side and a 6mm gap on the passenger's side (on the striker end). Seems more than just common targa/cab flex to me. I have something funky going on.

Rob, could be. My machine shop said it may have been balanced by the factory and could have come this way, but it was hard for him to tell. I have usually been running the standard Castrol or Mobil 20w-50 oils..

Another question for you: Is it ok to re-use the old cam chain sprockets with new timing chains? I heard that old chain should not be used with new sprockets, but was wondering if old sprockets can be used with new chain.

Matt, yeah look over the body carefully if you have that much door gap. My 1973 has a wider gap on the driver's side than the passenger side too, but I think it was just made that way. Hand-made cars and all that. I haven't measured, but I estimate 5mm on the pass side, and 8mm on the driver side, I'll try to measure later today.

"Another question for you: Is it ok to re-use the old cam chain sprockets with new timing chains? I heard that old chain should not be used with new sprockets, but was wondering if old sprockets can be used with new chain."

It depends.......
Why are you replacing the chains? If they are badly stretched/worn, then the sprockets will be exhibiting similar wear - they sort of work together as far as wear and tear goes. Hand and glove sort of thing. So.... your new chains will very quickly stretch to fit the wear pattern on the old sprockets. It won't take too long before the chain will resemble the old ones.
I just replaced 1 chain. But I had made a mistake and inadvertently untensioned a cam bolt using the chain for support. My guess was I had stretched part of the chain and stressed it beyond spec.
Alan

Does anyone know the spec for chain wear/stretch?