3.0 - Can you get away with it?

[The Donkey]

I am looking at an SC that is in need of a top end rebuild per the mechanic that looked at it. The compression was:
1-145
2-150
3-155
4-145
5-150
6-120

Due to the compression he did a leakdown on #6 and it was at 55%. He thought this was due to rings and he couldn't check for broken headstuds since the left side of the motor was wet due to leaky gaskets.

He did say that the car drives well and has good power but he recommends a top end.

My question: Is it possible that the compression/leakdown is wrong? How terminal is this reading if it is correct? and if it is terminal how long can you drive with it like it is with no apparent downside?

I guess what I am asking is should I go in and fix it just because the readings are bad but it doesn't appear to show in the driving.

Otherwise I guess I am looking at 2,500 to 5,000 on a rebuild?

Thanks guys.

[88-diamondblue]

Top end will be $2000-2500 to do it yourself and $3500-5000 to have it done IF the bottom end is good. How many miles on the engine? All depends on what the purchase price is for the car. I did a complete rebuild with new P&C's for around $6500 on a 3.2.

[The Donkey]

8.5k purchase. 95k miles on the engine.

What about the life of this engine before it throws up on me?

[BURN-BROS]

Not sure why he couldn't check for broken studs....If the engine has not been abused then you could expect another 100,000 miles out of it.Check for a broken stud(s). I have seen SC main bearings with 200,000 miles on them that looked like new!

[The Donkey]

Are you talking it can go another 100k even given the compression and leakdown figures quoted above?

[AFJuvat]

I rebuilt a SC motor a few years back that had low (constant 1 bar) oil pressure for 10 years. (o-ring on the oil pump was bad.) The bearings were still good.

I do not understand why he could not check for broken head studs either. It is simple to pop a valve cover off; particularly on the passenger side.

Repeat compression and leakdown on entire engine. Better yet, just have him do a leakdown. Have the mechanic clean and degrease the motor and look for oil leaks and check for broken studs.

If everything is ok other than cyl 6, you can easily drive it for a while before fixing it (track use not recommended). headstuds are another story.

AFJ

[Scott R]

I'm surprised that #6 fires with a %50 leak, I had 30% on #5 and when the engine warmed up, and it would no longer fire and that cylinder and another would drop.

I also started down the road of a top end rebuild, however I found that my cams were deeply pitted along with the rockers. This was all due to the cam spray bars being clogged up. This in turn was a result of dirty oil in the case from the PO, so I tore the rest of it down and found that the bearings were trashed and the case had sludge in it.

This has nothing to to do with anyone other than my rebuild, however it can happen.

[Eagledriver]

I would say you could drive it until it gets wore and starts to misfire. If it has a broken ring on number 6 the cylinder is probably scratched and might need to be replaced. I don't think you'll do much harm by continuing to drive it.

-Andy

[cstreit]

Well I'd at least consider making sure the leakdown isn't coming from misadjusted valves, and also removing the exhaust and engine breather hose to see if you can determine where the air is going. If you have a bent valve, valve not closing, or burned valve, continuing to run the car could prove disaterous. Chances are it's not any of those things, but I'd want to be sure...

[The Donkey]

The mechanic kept mentioning the ring is bad in the #6 cylinder. Can I not just fix the ring and be done with it?

[cstreit]

He could...

That's assuming it was the ring that was bad. Did the listen at the intake, exhaust, and engine vent to determine where the pressure was going?

Personally if I did ONE ring, I'd do them all, it won't cost much more and then you'd have a fresh top-end. No way to know that untill he's in there though...

[The Donkey]

Chris, great questions and I don't know the answer to them. It sounds to me like I should just run it for as long as I can and then when i start noticing an affect on performance then I take it in and do what is needed. about right?

[304065]

Hold it.

There is absolutely no reason why an oil leak would prevent your mechanic from removing both valve covers and looking to see if the head nuts were laying in the head, or if they could be turned by hand, both telltale signs of a broken stud.

Next: Did he do the compression test in order or randomly? Did he have a battery charger hooked up during the test? It's fishy to have the last two jugs test low, may be indicative of slower cranking caused by a dead battery.

Next: Why not check the leakdown on all the jugs, or at least the other low compression cylinder? Would be interesting to compare results: if he got 55% on all of them, it's reason to suspect leakdown technique e.g. engine not perfectly at TDC at the time of the test, or an engine in drastic need of a valve adjustment.

Next: Did he squirt oil into the low compression jugs to see if the compression improved? This is a classic way to isolate a bad ring vs. a valve. I don't know why he's certain a ring has broken.

Here's the point: a bad leakdown could be the result of a broken ring, leaking head due to a broken stud, a burned valve or a problem with the plug hole. If it's a bad ring, you should see blue oil smoke, and if you pull off the crankcase breather hose, you should smell, see and hear the blowby as the case gets pressurized.

If, on the other hand, you have a burned valve caused by improper valve adjustment (too tight, causing the exhaust gases to erode the seat) you could be looking at a catatstrophic valve failure with resulting damage to the piston, head, cylinder, rod, other valve, rocker and your wallet. But without the oil test to isolate the ring, hard to say.

If it were my engine I would borrow or buy one of those inexpensive borescopes to look inside at the valves. Or try a local aircraft mechanic.

[cstreit]

John's on the money. I definitely don't advocate driving it untill you are condident you know what the issue is. If the problem is bad rings you can get away with it for a while, keeping frequent oil changes as the oil would get very dirty from combustion.

However if the issue is a valve problem, a bent or burned valve, or even one that is too tight has a good chance of breaking off because the proper seating of the valve in the valve seat is responsible for a lot of the cooling of that valve. It can only overheat so many times before it weakens and brakes. It will then turn your piston, head, and probably cylinder into scrap metal.

Be SURE.

[The Donkey]

Thanks guys. It really drives very well but I am having RickV do another compression and leakdown on the engine before I go further on what to do. The only smoke from the engine is from the leaks from the Oil Sender and the front cooler. I will post again for an update. Honestly though, if you didn't know the numbers on the engine that the mechanic gave me you wouldn't have any idea there was anything wrong with the engine. It pulls hard and sat in stop and go traffic for 6 hrs coming back from NJ and never got over 1/2 way on oil temp. that was better than my Carrera.

[Eric-325I]

Mr Donkey:

For reference: I bought my '79 SC coupe, silver over black with a recently over-hauled tranny and tight motor (100k) for 10k last summer. Although I am aggressively digging into her (rs carpet, doors, backdating, etc.), all she really needed was some trim pieces replaced and very minor bodywork on one small area.

8.5k sounds like a lot for an SC that most likey needs at a minimum a top-end.

Eric

[The Donkey]

Eric, I think you got lucky with that buy. That is a hard find and I think that most will concur. 10k for an SC in good shape, with rebuilt tranny and 100k on the motor is a good deal. In my opinion, I think that is a 12k to 13k car on the East Coast. So, looks like you did well. I am really not that concerned with a few thousand. I am more concerned with finding the car that I want, color, interior condition, wheels, exterior chasis straight with no rust, etc.

[crashmy911]

How is the shape of the rest of the car. Is everything else pretty perfect? I would spend 8 on a car with a suspect motor if the rest of the car was perfect.

[The Donkey]

Rest of the car is A- to A. Suspension does need to be refreshed but body is rust free and paint is excellent. Sport Seats and rest of interior is in excellent shape. Tranny is strong. I already bought it and had a bunch of Pelican's out today and they were very impressed. We found that it also had H4's, 8x7's, SSI's, 2 in - 1 out upgraded exhaust, etc.

[The Donkey]

Update. It haven't had another leakdown and compression done just yet. When the other Pelican's and Dorki's came out to look at it they think that there is a remote possibility that it could be due to carbon buildup in the engine (remote possibility mind you). The engine drives very well they thought but there is a slight tapping in the engine that could be indicative of carbon build up since the car was rarely driven and when it was it was driven on short jaunts. The tapping is not always consistent and can actually get a bit better at times when it is run more.

So, they had me go get some BG 44K and run it through a tank of gas at high RPM and see if the knocking goes away.

Well, I am about 3/4 of the way through the tank and the engine is running just fine. Oil pressure is good (5 or 6 at start up and 4.5 or 5 in normal driving. At idle it is around 1). OEL level is good and Oil temp is nice and low. It is smoking much less, at start up, than it was just a few days ago and seems to be running actually better than it was when I got it. The tapping is still there but at the end of my 160 mile run yesterday I actually wasn't sure if it was there or not when I got out of the car to pull in the garage.

Any thoughts on this? I know nothing about motors but am trying to learn but my Pelican/Dorki buddies are very knowledgeable and one of them is a BMW/Porsche mechanic full-time. I trust their judgement but am open to hearing other ideas.

Thanks.