When to rebuild vs. top-end only?

[Danny_Ocean]

Where is the line between a top-end rebuild vs. rebuilding the entire engine?

My motor (stock '79 3.0) has 138k and runs well, although there are numerous oil leaks (including at base of cylinders) and the "start-up" smoke is getting worse.

I imagine there is a point where it makes financial sense to rebuild the whole thing, but if the bottom end is going to last another 100k, then why touch it?

I only put about 500 ~ 1000 mi./year on my car, further complicating my decision.

[Laneco]

IMHO, with no displayed issues in the bottom end, do top end and headstuds.

Then enjoy it at 1,000 miles a year for the next 100 years.

angela

[DanielDudley]

What is your oil pressure when hot ? That would tell you your bearings are tight. Compression and leak down tell you your rings are good.

[gregwils]

The start up smoke could be valve seals or guides. Oil leaks at the bottom of the cylinders could be broken head studs. I agree that you should start by having a compression test and cylinder leak down done first. Low compression or high leak down would tell you that you have an issue that needs addressed.

You should try to have an experienced air-cooled porsche mechanic do the compression and leak down. They could tell you whether you have excessive wear in the guides by the amount of radial play. 3.0's can be pretty robust if you don't have broken head studs.

[JeremyD]

At 140K miles - I'd open up the bottom -

[porschenut]

Originally Posted by Danny_Ocean

I imagine there is a point where it makes financial sense to rebuild the whole thing, but if the bottom end is going to last another 100k, then why touch it?

I think it makes poor financial sense to just do a top end at 138k. The majority of the rebuild cost is in the top end anyway, and it's not much more work to do the rest.

You can't reasonably assume it will go another 100k. There may be wear in there that will show itself very soon. Very, very few of these cars go 300k, despite a handful of reports that represent the extreme exceptions rather than the rule. It's a roll of the dice to do just the top end.

[hcoles]

I rebuilt the top end on my 3.2 at 75k. I did all the "while you are in there" including rings and didn't open the bottom. At the time I felt like I was pushing my skill limit and didn't tackle the bottom, but I probably should have. I would say at 130k you should open the bottom up and replace e.g. layshaft bearings and of course anything else that needs it. Others here can provide much better and more complete advice. It might also depend on how long you want to keep the car.

[Rot 911]

I disagree with the other posters on opening up the bottom end, UNLESS, you have signs of low oil pressure. On my 3.2 my valve guides were shot at 130,000 miles so if figured might as well rebuild the whole engine, which is what I did. I rebuilt it myself and as I took things apart I discovered every wear item on the bottom end was still well within spec. Hell, everything but the valves, stem seals and guides were in excellent shape. Still I replaced everything as "I was already in there," but in hindsight I could have saved a lot of money just rebuilding the top end. Upon talking with others later I have learned that the bottom end of the 3.0 and 3.2 engines can easily go 200K or much, much longer.

[andyt11]

I'm in exactly the same position as Rot. I'm doing everything down to rod bolts and shells, timing chains, ramps etc.... but the crank has very little end float and shows no signs of wear at all. It's easy for people to sit there and say you should do it all, its the safest answer (so they can't be wrong) and they are not paying for it.

See what you've got once you get in there and have someone with experience look at it. May well be acceptable to leave the bottom end alone.

[Danny_Ocean]

Oil pressure is good.

I plan to keep the car awhile, but I don't see increasing my driving. I have a typical routine...beach, shows and the occasional cruise. It never will be a daily driver or track car.

So...can the bottom end be examined/measured without disassembly? How much does a complete rebuild add to the cost vs. top-end only?

[CorsePerVita]

I'm at around 180k and my car runs soundly. Little puff'o'smoke at startup, once she's up to operating temperature it's sound as can be. Uses a pretty normal amount of oil thus far. When I had a PPI done they said it hadn't been opened up from what they could tell. Although I have a feeling with this sort of mileage the top end may have been done at an earlier time. Hard to know for sure.

[Tsunamiboy]

I got 214,000 miles out of my 1979 3.0L without the motor being opened up for any major work. I took the easy way out by swapping out for a late model (1987) 3.2L

As long as your 3.0L isn't polluting or pouring oil out just keep driving it.

I can't imagine driving only 500-1000 miles a year. Mine is not a daily driver but I am committed to driving the wheels off my SC. I would rather wear it out then have it as part of my estate

[Danny_Ocean]

Originally Posted by Tsunamiboy

I can't imagine driving only 500-1000 miles a year. Mine is not a daily driver but I am committed to driving the wheels off my SC. I would rather wear it out then have it as part of my estate

Well...it's slammed with some pretty wide/stiff rubber, so no the most comfortable car to drive. And, having no A/C (yet) makes it pretty undriveable from Apr. ~ November.

[ninesixfour]

Originally Posted by Danny_Ocean

So...can the bottom end be examined/measured without disassembly? How much does a complete rebuild add to the cost vs. top-end only?

I think I bent a valve at the track last weekend due to an over-rev, and I am contemplating the same thing right now. For reference, my mechanic has quoted me 30 hours for a top end not including head stud replacement, 55 for a full including head stud replacement, balancing, and port matching. As others above mentioned, the difference between the two options, when you factor in the additional labor and parts cost, is not insignificant, and in my case is more than $3K. This assumes my Ps and Cs are reusable.

Other than the compression being a little low, oil pressure has been perfect, and oil consumption was very low considering it has 113K on it with no broken head studs, and it has seen nothing but track time for the last 3 years. I am leaning towards just the top end with the addition of the head studs. If I need new Ps and Cs, all bets are off.

[RWebb]

a sequence of oil tests might reveal metals from the bearings

if no problems you might just do a top end -- these motors can run 300 - 400k miles in some cases

also it is not hard to pull the engine if you need to redo it later on

[Gemballa2006]

My opinion is with that mileage do them both, the bottom costs very little in relation to the top, and whats the worst that can happen, you do it and it didn't need to done, big deal your out a few bucks but have piece of mind, on the other hand, you only do the top to realize 5000 miles from now you need to do the bottom, now you are doing it all over again, seems like a watse, I would do it as insurance for the money you are spedning to do the top. I just did this on my 1986 with 140,000 miles. Runs like a champ now, well minus the starting issue, but that was there before, haha.

[83_Silberpfeil]

Very interesting discussion/points-of-view.

I'm rather new (8 months) into an 83 SC ownership --- 157K.

What's actually the scope of work for Top End vs the Bottom end?

Hope I'm not opening up a can of worms!

[5String43]

When the top end on my car's engine was done last summer, the guys at the shop said the hot tip was to pull the number-five rod and look at that bearing, because for some reason it was the one that usually sees the most wear. It looked like new, they said, so they buttoned the bottom back up. But that seems to me like a pretty good barometer.

[RWebb]

Originally Posted by Gemballa2006

My opinion is with that mileage do them both, the bottom costs very little in relation to the top, and whats the worst that can happen, you do it and it didn't need to done, big deal your out a few bucks but have piece of mind, on the other hand, you only do the top to realize 5000 miles from now you need to do the bottom, now you are doing it all over again, seems like a watse, I would do it as insurance for the money you are spedning to do the top. I just did this on my 1986 with 140,000 miles. Runs like a champ now, well minus the starting issue, but that was there before, haha.

this makes sense, esp. for DIY - it's just a small bit tricky to get everything laid out; check carefully (maybe do some dry runs); goop it up; and.... before it dries

[brads911sc]

I would do both.

gives you a chance to check everything, replace the intermediate shaft bearings, etc.

You are out the cost of bearings, rod bolts, and case sealer/seals and thats about it except machine work unless you find something wrong... and youd want to know that anyway.

I had pitting on my intermediate shaft bearing surface. So It added $750 to my build. But would I really want to spend 10k+ and not have resolved that? way too much work to do it half way at that mileage.

For every 1 sc engine you see on this board that last 300k there are 10 that did not. It is not reasonable to make that assupmtion.

Originally Posted by Gemballa2006

My opinion is with that mileage do them both, the bottom costs very little in relation to the top, and whats the worst that can happen, you do it and it didn't need to done, big deal your out a few bucks but have piece of mind, on the other hand, you only do the top to realize 5000 miles from now you need to do the bottom, now you are doing it all over again, seems like a watse, I would do it as insurance for the money you are spedning to do the top. I just did this on my 1986 with 140,000 miles. Runs like a champ now, well minus the starting issue, but that was there before, haha.