So, what is a "top end rebuild"? 3.2

[aigel]

A "top end rebuild" is what I am intereststed to learn about. Seems this can be anything from just redoing the heads to rebuilding / replacing everything short of cracking the case. Is there a true definition?

So, let's say I am on a budget and want the typical 150k mile 3.2 to quit smoking because of its typically worn guides: I need a minimum of the valve guide / head work done. One would also want to put the steel studs in the bottom side for preventative maintenance.

Would you even consider taking the p/c apart if there is good compression, no indication of cracked rings or other signs of bad health? So, can the 'top end rebuild' be the heads and new exhaust side studs?

Thanks,

George

[Doug Zielke]

It's a good question you have there, George.

When I dropped my SC's 3.0 (80k miles) two years ago for head stud repair, I planned to do just that, plus a reseal, and no more.

On good advice from people I trust, I decided not to split the cases on such a relatively low-mileage motor. However, I was advised to pull off a rod or two and check the bearings. I did that (there was no measurable wear), and of course that meant the p/c's had to come off....

While the original Kolbenschmidt Alusils were well within spec, I discovered a *broken* oil ring on the #4 cylinder. Who knows how long the motor had run like that? A mechanic who I asked, said he'd seen it before, with no real loss of performance. These motors just seem to soldier on!
I ended up installing a new Mahle p&c set, mostly because I sourced one at a good price. I probably could have just re-ringed the KS pistons like so many have done.

The rest of the work consisted of new seals and gaskets everywhere, steel head studs, total re & re of the heads (by a local expert), reconditioned rockers and a host of other small items to numerous to list. It all adds up.

In the end, I did more and spent more than I originally planned. I replaced quite a few parts that *may* have been serviceable for a while longer. However, the motor runs stronger than ever. It is leak-free and uses *no* oil. I'm completely satisfied with the route I chose.

[HarryD]

Hi George,

I just faced the same issue with my Magnesium cased 2.4 liter. When we pulled the heads, the cylinders looked ok and we decided to leave them alone. Bear in mind that cracking any magnesium case requires significant machine work to properly reassemble. Your aluminum case may be far less costly.

In my my mind, a top end is renewing the heads and, maybe reringing. Of course, while the engine is out, all accessible seals and gaskets should be replaced. The cylinders should be inspected, measured to verify roundness and wear. At 150k, I would consider pulling at least one cylinder off to look for rod bearing wear as well. As others here have noted, you might want to get your oil filter cut open to look for evidence of main bearing wear.

As in all planning, plan/budget for the worst and hope for the best.

[88911coupe]

Excellent question which I am asking myself since my 88 with 130k on the clock is using oil pretty quickly but only has a puff of smoke on occasional start ups. If I look at the drain plug and the oil filter and find no metal can I be relatively sure that nothing is broken inside? If the pistons look clean, i.e no excessive wear, should they be left alone? Do you open a can of worms replacing rings if the ones in there look fine or should these be replaced as a matter of course?
Thanks

[HarryD]

Originally posted by 88911coupe
Excellent question which I am asking myself since my 88 with 130k on the clock is using oil pretty quickly but only has a puff of smoke on occasional start ups. If I look at the drain plug and the oil filter and find no metal can I be relatively sure that nothing is broken inside? If the pistons look clean, i.e no excessive wear, should they be left alone? Do you open a can of worms replacing rings if the ones in there look fine or should these be replaced as a matter of course?
Thanks

Part of the reason we chose not to replace the rings on my rebuild was the risk of them failing to seat properly (new rings/old cylinders) while we had no indication of any problems with the existing ones.

As the old saying goes: "You pays your money and you takes your chances".

[aigel]

If you have nikasil cylinders, can you just buy new rings and hone the cylinders with a ball hone to help seat the rings properly?

I think that these air cooled engines are pretty hard on pistons, the ring grooves tend to wear out. They just get much hotter than a water cooled engine in that area. Once you pull the pistons and measure the piston groove wear, I guarantee you that you'll probably want to buy new pistons. Then, unless you have Nikasil cylinders, you are in it for a high $ ride...

Boy, you guys really pull a rod bearing and then stick it back in? That's an adventure! I would be scared that it won't be the same after that intrusion. Doesn't the rod clamp down on the bearing and help hold it in place that way? Especially on a well worn assembly, I'd be scared I'd loose some of that clamping force and set myself up for a spun rod bearing. After opening things up on the rod bearing side, I sure would not want to put it back with the old bearing and non-resized ends!

We'll see. It is my pal's engine. I am just trying to get a feel what he is in for. I'll do the labor, but he needs to pay for the parts! I understand that one has to play it by ear, depending on what's found. All we want to achieve is another 50k miles.

George

[HarryD]

Originally posted by aigel
If you have nikasil cylinders, can you just buy new rings and hone the cylinders with a ball hone to help seat the rings properly?

I think that these air cooled engines are pretty hard on pistons, the ring grooves tend to wear out. They just get much hotter than a water cooled engine in that area. Once you pull the pistons and measure the piston groove wear, I guarantee you that you'll probably want to buy new pistons. Then, unless you have Nikasil cylinders, you are in it for a high $ ride...

Boy, you guys really pull a rod bearing and then stick it back in? That's an adventure! I would be scared that it won't be the same after that intrusion. Doesn't the rod clamp down on the bearing and help hold it in place that way? Especially on a well worn assembly, I'd be scared I'd loose some of that clamping force and set myself up for a spun rod bearing. After opening things up on the rod bearing side, I sure would not want to put it back with the old bearing and non-resized ends!

We'll see. It is my pal's engine. I am just trying to get a feel what he is in for. I'll do the labor, but he needs to pay for the parts! I understand that one has to play it by ear, depending on what's found. All we want to achieve is another 50k miles.

George

Hi George,

No, we did not touch the jugs on my rebuild. They looked ok and at ~100,000 miles we figured it was good enough. If I was at $150,000+ Ii might have felt differently due to both bearing and ring land wear issues. Of course, iIneeded to be careful since, with my Mag engine, splitting the case has serious $$ issues and upgrading to a 3.0 would be a very viable alternative. If you consider that I cannot just replace my NLA P&C's, it just makes the decision that much easier.

[Rot 911]

How about some input from someone that just did a complete case up rebuild of an '86 3.2 Carrera? Mine had 133,000 miles using a quart of oil every 300 miles. Bad compression and leakdown on two cylinders that once I got the heads off were attributable to burnt exhaust valves. Every other internal part on the engine was withing standard specs. The cylinders still showed the factory hone marks (Nikasils). I had already committed to a complete rebuild, but in hindsight could had the heads rebuilt and probably gotten another 50-60K more miles out of the engine. Maybe more.

[aigel]

Kurt:

Great input!

So, let's say I find a broken ring or another reason to re-ring. Can I run my flex hone (ball hone) through the nikasils and be done with the cylinders? Or is the honing something to be left to the machineshop. I have re-ringed many steel block domestic engines but am unsure about the flat six, if it comes to this...

TIA, George

[Rot 911]

Unless the cylinders are scratched or out of spec, Wayne in his book recommeds flex honing, which is what I did.

[davidl]

I would personally advise the whole strip .

The time taken to R+R the case and crank, clean and check the parts is far less than the time needed to repair and rebuild the heads alone.

And I'd want to put decent rod bolts in there too...

I regularly find totally unexpected problems.. of course, you may not want to know!

The way I see it, it is cheaper to get a good used engine than do a part-rebuild...so why choose to rebuild at all unless you want complete peace of mind.?

kind regards
d

[aigel]

Ok. I read more in Wayne's book. He speaks of a micro thick layer of Nickel with Silicon/Carbide. How thick exactly is that layer? And when he talks about a 'special' silica hone, that's what a ball hone is, right? The thing that I have hanging on my wall ?

I hear you, david. Good points you make. A used engine with a warranty is NOT cheaper than a top end, not cheaper than a complete rebuild, actually. A reputable dismantler typically will quote you $6500 if you bring back your bad engine and probably around 8k for an outright purchase!

The plan here was just to get the valve guides taken care of and get 50k more miles out of it. Then it will be 3.6 time.

Cheers, George

[davidl]

Ah, that's differnt than round here!

A good 3.2 is between 4,000 and 5,500, 3.6 similar. 3.0 less.

Makes a big differnece.

I'd estimate the time to fully do the bottom end assuming all in order at 10 hours at most..less than a day.

kind regards
david