machining advice

[OG911]

my 85 3.2 is out and disassembled - engine looks pretty darn clean on the inside after 220,000!- there was nothing catastrophic, just decline in power- pretty significant leakage on exhaust valves- split case as long as i was in the neighborhood and the engine has this much mileage....- building back stock so no necessary regrind for cams, etc

my question now is where to send for various machine work- have seen the various recommendations for shops - easy enough to say ollies, but i cant wait a year for a turnaround-so...heads will go to hoffman near atlanta- that is all they do, unfortunately!- am curious whether i can send crank and cams to be miced and polished to local speed shop or whether the recommendation would be to locate another porsche specialty shop- thoughts there?

and what advice re pistons and cylinders and rocker arms?- they look great- no pitting- is the usual drill to simply hone cylinders after measurement- what is likelihood i can use standard 95 rings on the rebuild or should i anticipate oversize?

basic stuff for you guys- firsrt rebuild for me- thanks for the help!

[PeteKz]

First question is always, "How much budget do you have?" then, "are you doing this yourself, or paying a shop to rebuild the engine?" And then, "street car or race?"

I'm sure I'll get some counterarguments, here's my take for a STREET car:

The 3.0 and 3.2 aluminum cases are very robust. Unless you see or measure something out of spec, do not send it off for machining. Check the rod bearings for clearance. If those are within spec, LEAVE THEM ALONE. Only replace the rod bolts.

If the rod bearings are within spec, then the main bearings almost certainly are too. Do a test assembly with Plastigage and see if they are the same or there are significant variations among the bearing clearances. If the mains are good, leave them alone too. Replace the intermediate shaft bearing shells and check the other internal parts and especially the oil pump. If any questions about the oil pump, replace it or get it reconditioned. Those do tend to accumulate wear. Then put it back together with the ORIGINAL bearings. You will save yourself a boatload of time and trouble, not to mention money. Use new oil seals. Check the intermediate4 shaft gear and can drive sprocket. If within spec, reuse them.

To reassemble the case, use the recommended sealants in another thread on this forum.

Pistons cylinders. Measure and renew only as necessary, unless you plan to increase displacement to 3.4, which will require a new set of P/C's and about $5000.

Heads: replace the valve guides and recondition the valves and seats. Reuse the springs unless out of height spec, and retainers unless worn or out of spec. Send these to a shop that specializes in 911 heads.

Cam and housing: Are you going to use a different cam? Different intake and fuel injection system? Lots of discussion about various cams and pro's and con's on this Forum. Peruse those. Check the cam bearings for wear, but unless they got contamination in them, they should be good.

Rockers and rocker shafts: These probably are showing wear, so recondition or buy new, especially if you are installing a different cam. Use the RSR O-rings!

Cam chains and sprockets: Inspect carefully, but reuse if they are not worn.

Buy your gaskets and seal kits from Wrightwood Racing.

That's not the detailed response, but should get you thinking about how to proceed, and provoke counter replies! .

[OG911]

thx, pete- that helps- basics: will be a street rebuild- same cams- i am doing the teardown and reassembly- machine work by others- budget?- who knows, but will do what it takes

re the plastigauge recommendation...- is the process to plastigauge each of the rod clearances first, determine that they are all within spec, and then plastiguage the mains and torque the case?- am wondering re your thought that if the rods are good, the mains are as well

am pleased at how clean the case is inside after 220000!- it sure doesnt guarantee that things arent worn but it's a good start- if the case/crank went to the shop to be measured, any guess re probable cost to measure these clearances by instrument- is concensus that plastigage is good standard for street build?

[PeteKz]

The rods get oiled via holes drilled diagonally through the crank from the main bearings to the rod bearings, so they are further downstream and get less oil flow than the mains (ignoring the centrifugal pressure effect). Therefore, if the rods didn't suffer from lack of oil or poor oil, then it's even less likely the mains suffered either.

NOTE: several people here have measured NEW Glyco bearings out of tolerance, and with poor design. That's why I say to reuse your rod and main bearing shells if they measure out. Plastigage is not the way Porsche does it or specifies it, but IMO it's plenty good enough to check that they aren't out of tolerance. If you are building a serious race engine that will see 8000 RPM+ and you want .0025"-.0027" main clearance (2 ten thousandths), use the expensive measuring tools (and know how to use them). If you are building a street engine, and you are satisfied with .002-.0025" clearance (which is well within Porsche specs), then Plastigage is good enough.

Use the Plastigage on the rods. use the old rod bolts to torque them to spec, and then check the Plastigage squish. On the mains, bolt it together (you only need to do the case through bolts), then show us what you got.

Cost having a shop measure the case and crank/rods: I have no idea. Let's see if anyone else jumps in.

[brighton911]

Alucil cylinders (10 fins) cannot be re-ringed as the unique rings are not available. Hopefully you have Nikacil cylinders (11 fins) that can be re-ringed. Nikacil cylinders need to be honed in a special way, do not use a conventional hone. Scotchbrite pads on a spring arm hone actually work quite well to clean up but not cut the finish. I used soapy water as a lubricant.

[mikedsilva]

For what it's worth, I use boregauges, micrometers and plastigauge to double check.

For a street/home build, plastigauge is more than acceptable. I've never had success being able to do the rods with plastigauge though.. not sure how people manage to torque the rod bolts without the rod moving.. maybe that's me? I always use mics and bore gauges.

I never re-use bearings. I've only once or twice come across bearings with zero marks or wear. And even if they look perfect, I just cannot bring myself to re-use them. For your rods, def do not use the Glyco bearings. Use the Automobile Associates style or if available, look for ACL bearings. They come in std size and "extra clearance" sizing and they are extremely accurate.
For the mains, the Glyco tend to be ok but I usually go with Gen Porsche GT3 main bearings.

When you bolt your case halves together with the crank, make sure to use the #8 bearing too. It is the "locating dowel" at that end of the case.

I target 2 thou clearance on mains and rods.

As sturdy as the aluminium cases are (compared to Magnesium), I've never come across one that measures within the Porsche spec of 65.00-65.019 mm. Never.

People say that Alusil cannot be re-ringed cos Wayne's book says so. Others have done it. Some successfully. Some not. I have not come across a client willing to take the risk yet. So I have the cylinder replaced or re-plated with Nikasil and get replacement pistons and suitable rings.
If you look at the parts listings on this site for rings, they say they are suitable for BOTH Mahle and KS cylinders.. but how can that be possible?

Others have said they buy them from here, but when I have asked for part numbers so I can order some, the trail goes dry... I tried speaking to the reps at this site, but they couldn't assist.

As for Alusil being no good, well, it is used widely in lots of other makes and lots of other Porsches. I recently rebuilt a 3.0 with Alusil.. it had travelled 250,000 kms. The cylinders looked like new and the rings were also in great condition.

[OG911]

Can put the alusil question to rest. Mine was a grey mkt/row car back in the day. Nikasil

Is my local speed shop set up to hone?

[PeteKz]

Another basic question: Did you do a compression of leak-down test before pulling it apart? What did that show? Was the engine burnin excessive oil?

If the cylinders look good, get them and the pistons measured too. Check the side clearance between the rings and the lands. Then put the top ring of each piston into the same cylinder it came out of, and measure the ring end gaps. It's entirely possible those are still within spec and can be reused, as long as you put the same pistons and rings into the same cylinders they came out of.

Save some green for the next thing I will suggest: New M1 cams. These will be $1000 for the pair. If you're interested, contact William Knight (he's on here as Knightrace). These won't make a huge difference, but they will extend the power and torque curves and were designed to maximize performance using the stock pistons.

[boyt911sc]

Originally Posted by mikedsilva

For what it's worth, I use boregauges, micrometers and plastigauge to double check.

For a street/home build, plastigauge is more than acceptable. I've never had success being able to do the rods with plastigauge though.. not sure how people manage to torque the rod bolts without the rod moving.. maybe that's me? I always use mics and bore gauges.

I never re-use bearings. I've only once or twice come across bearings with zero marks or wear. And even if they look perfect, I just cannot bring myself to re-use them. For your rods, def do not use the Glyco bearings. Use the Automobile Associates style or if available, look for ACL bearings. They come in std size and "extra clearance" sizing and they are extremely accurate.
For the mains, the Glyco tend to be ok but I usually go with Gen Porsche GT3 main bearings.

When you bolt your case halves together with the crank, make sure to use the #8 bearing too. It is the "locating dowel" at that end of the case.

I target 2 thou clearance on mains and rods.

As sturdy as the aluminium cases are (compared to Magnesium), I've never come across one that measures within the Porsche spec of 65.00-65.019 mm. Never.

People say that Alusil cannot be re-ringed cos Wayne's book says so. Others have done it. Some successfully. Some not. I have not come across a client willing to take the risk yet. So I have the cylinder replaced or re-plated with Nikasil and get replacement pistons and suitable rings.
If you look at the parts listings on this site for rings, they say they are suitable for BOTH Mahle and KS cylinders.. but how can that be possible?

Others have said they buy them from here, but when I have asked for part numbers so I can order some, the trail goes dry... I tried speaking to the reps at this site, but they couldn't assist.

As for Alusil being no good, well, it is used widely in lots of other makes and lots of other Porsches. I recently rebuilt a 3.0 with Alusil.. it had travelled 250,000 kms. The cylinders looked like new and the rings were also in great condition.

OG911,

READ AND PRINT THE ABOVE POST (by mikedsilva). You would probably not get a better recommendation than this one. The most expensive costs or expenses in engine rebuilding are LABOR, cylinder heads machine work, quality main and rod bearings, and heaven forbids crankshaft work. Since you are doing the rebuild yourself, why use old bearings with 220,000 miles on them? Alusil cylinders in good condition could be re-ringed. PROOF: I have in the garage a ‘78 SC track car with almost 20,000 track miles rebuilt more than 25 years ago and still running well plus more than a dozen engines I had rebuilt and counting.

You will need to use precision metrology tools to measure the bearing clearances. I could not imagine bringing my car to a shop or mechanic that has no tools and using tape measures for precision evaluation. Wish you good luck.

Tony

[OG911]

have no intention of taking parts to a shop that has no tools or uses tape measure- am headed in direction suggested by pete and mike that plastigage is good measure for a rebuild to street standard

as to the m1 cams...anyone else out there really like these?

the cylinders look immaculate- car never burned oil- the leakdown test produced no audible leaks in breather but lots of loss in exhaust valves- a couple of cylinders had 95 in and could hold about 30!- am wondering why i wouldnt automatically re-ring??- cyliders and pistons are matched and bagged- what possible advantage to re-use rings?

and a bump on question of whether the local shop can hone cylinders or whether those should be shipped off?- what is special about the nikacil hone?

[OG911]

oil pump...- what am i looking for in terms of indications of wear?- or is it best practice to heve rebuilt?- any suggestions re shop to do that if necessary?- thx guys

[targa72e]

what is special about the nikacil hone?

Nikacil is very hard and generally does not require honing to reuse. If the cylinders measure in spec for ovality and bore size you can generally clean them and put in new rings with no need to hone. Plenty of info on this site on how to do that. As mentioned ring land clearance and piston to cylinder clearance need to be measured as well. If cylinders do need to be honed there are special hones needed (diamond I believe) and surface RA finish is important as well.

john

john

[OG911]

can i beg an explanation regarding ring land clearance?

[PeteKz]

Ring land clearance is the space between the ring and the land. You typically measure it by inserting a feeler gauge between the ring and the lands and checking all around to make sure it's even and within spec. Porsche calls this the "piston ring height clearance." From the Tech Specs, for SC engines it should be:
Comp ring 1: .070mm to .102mm, wear limit: .20mm
Comp ring : .040mm to .072mm, wear limit: .20mm
Oil ring 3: .020mm to .052mm, wear limit .10mm

If there's any carbon down in the grooves on the piston, clean them out very carefully. You do not to want to gouge the tops and bottoms of the ring lands.

To borrow a quote from Smokey Yunik (RIP, famous NASCAR mechanic and designer), the seal between the rings and bottoms of the lands is the most important seal in the engine.

[PeteKz]

Oil pump: I don't know if anyone rebuilds them. I would think if anyone does, Ollie's would. When I did my last rebuild, I used a Turbo pump with a cast iron housing. I rebuilt my engine 3 years ago because the oil pump scavenge side was not keeping up with the pressure side, so the case was gradually filling with oil, until the crank was constantly running in the oil in the crankcase, and was getting intermittent oil starvation due to low oil in the tank. I discussed this with Alan Caldwell, both because he was the PCA national tech advisor, and because he was relatively local to me (in Seattle, until his passing last year). He said he had seen this on SCs under certain conditions. Rather than trying to rebuild mine, or buying a new one, I got a deal I couldn't refuse on the Turbo pump, which pumps more oil, and has a proportionately larger scavenge pump section. So that's what I used.

With respect to mikedsilva for his expertise, I understand the urge to put in new bearings and rings. If you just want to, hey, it's your engine, do what makes you comfortable. But if you want to conserve money for other purposes (like suspension and tires!), then there is no reason to replace parts that measure within the specs. That's why Porsche (and every other manufacturer) provides those specs. Journal bearing shells do not wear out in normal operation. They wear because dirt got in the supply oil system, or lack of oil. The crank main journals and crankpins rotate on a film of oil that prevents metal-to-metal contact. Otherwise, they could not last several hundred thousand miles in the first place.

The Plastigage check will help you decide.

[stownsen914]

Re: cylinders, if leakdown was good prior to teardown (sorry if I missed this detail in the thread), no reason to not just reuse the rings and reassemble. If you are re-ringing, many will say to hone the cylinders, not to change them dimensionally but rather to introduce some texture to encourage new rings to seat. A shop experienced in Porsche machining (or just familiar with nikasil cylinders) will know what to do.

Re: checking the oil pump, it’s not hard to check them if you know what to look for. Mostly looking for scoring or pitting on the gears and the pump bores. Look up Glenn Yee, and Supertec or other Porsche shops can do this.

[zztot]

Glenn Yee is the premier oil pump guy. PartsKlassic (and others)/sell his “reconditioned” pumps ….PartscKlassic recently 435 exchange …..yours must be good but sounds likely.

[OG911]

plastigage results: rods all at .002 or better- only item of note is wear evident at #3 - it is "fingernail-worthy"- should i conclude it is to be replaced?- and if so, only that rod set?- all other surfaces very nice



mains at .002, except #4 at say .0025- bearing surfaces smooth, with no pits or scoring- pic is typical of all mains- what advice re replacing #4



re rocker shafts- confession here!- you tube makes it look easy- wasnt bad for most but i struggled mightily(!!) with last two- intakes #4 and #5- twisted a 5mm allen in the process- nothing worked- even tried drilling- i finally drove them out with a drift - (two new shafts added to order) -from here, any necessity to refinish inside of cam housing thru which they were driven?- and any necessity to refresh rocker bearings generally in absence of issues?

[OG911]

[PeteKz]

The main you showed looks good in the picture. I would reuse them if they all look like that and measured .002"-.0025". The rod bearing I would replace, even if it measures in spec. There are specks of something on the rod bearing shells. Are those embedded in the shell, or just something from the shop that got on the surface before you snapped the pic? If that's crap in the shell, how does the journal on the crankpin look? Any grooves in that? You could just replace the rod shells that need replacing, but you generally have to buy a full set in a pack, so you might as well replace them all.