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Gon fix it with me hammer
 
svandamme's Avatar
 
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biral vs nikasil

Howdie guys, i'm busy looking to score a new set of P&C's ( amongst some other things)

and came to the following


machine shop that's doing my case, has a set of Nikasil 2.4S Pistons &cyllinders for about 2000 Euro ( about 2500 of your US dollars)

they insist that they can't find any more Birals , which my engine originally had


i was told , that the Birals , should be better, at preventing the pulled studs problem, since they expand less than nikasil


machine shop didn't quite believe it , so they took 2 same size cyllinders
on biral, one nikasil, and heated them up to 150 Celcius

they claim the difference was 0.05 mm


is that enough difference to cause pulled studs?



what to do?
Nikasil should last longer
Biral is original


anything else i need to consider? does anybody have experience with 2.4 S Nikasils on a 5R case, original steel studs ?
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Stijn Vandamme
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Old 10-20-2004, 02:06 AM
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Stijn,

First off, what is it you are trying to accomplish?
Is it important to remain absolutely original?
Is original appearing OK?
Is the goal to have a good running and long lived 911 engine?
Is cost the determining factor?
Do you want more power?

I assume the 2.4S Nikasil are new replacement parts.

I assume the test results were where the Nikasil cylinder expanded more than the Biral cylinder. I donít think 0.05 mm (~0.002Ē) is a significant difference.

Nikasil are longer lasting, more tolerant of high heat, have better heat dissipating ability, and better ring sealing. In short, I would always use Nikasil given the choice. The price is in the normal range.

Another possible option might be to send your cylinders to someone (in the States?) for boring and fitting other new (JE?) pistons.

If I were at the stage you are, I would opt for 2.7RS Nikasil (easy) or 2.8RSR Nikasil (lots of work.) The repaired 5R case will work just fine but you might try and find a good (new or virgin) 7R case. Regardless, you should use inserts in the case for the cylinder studs. There is a lot on this Forum about that subject.

Best,
Grady
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Old 10-20-2004, 07:50 AM
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my 5 R case has been rebored to original spec, and oil bypass done as well, so i'm sticking to the 5R case

i'll keep the 2.4S displacement, cause i have the S mfi pump to go with them...

is it very obvious to tell if a case allready has certs?
there seems to be something around my studs, but wasn't sure if that would be stock , or certs , seems to be a bit different colour



i'de prefer not to touch the studs if i don't really have to , they weren't pulled when i got the engine, why fix it if it ain't broken

but don't want to install nikasil 2.4's if the nikasil change would instantly result in pulled studs
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Stijn Vandamme
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Old 10-20-2004, 08:05 AM
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Stijn,

It isnít obvious from your picture if you do or donít have case stud inserts. I may see an insert at #1 cylinder upper left stud and #3 cylinder upper right stud. It is hard to tell from Denver. Helicoils are usually difficult to see. TimeSerts and CaseSavers are usually easy to see. If all studs have some sort of insert, leave them alone. If only some have inserts, install new inserts where they are none. If there are no inserts, do the right thing and have the best possible case with the best inserts and studs. Donít forget the case stud at the jackshaft bearing.
All of us will be disappointed if you have to go back and add inserts later.

You do not have to send your proper running MFI pump in for recalibration when changing to 2.7S or 2.8S from 2.4S. There is a simple way to shim the aneroid to have proper mixture. The pump is more than capable of supplying proper fuel mixture.

I would use the Nikasil cylinders in a flash. They are far superior to Biral. Your concern about expansion is valid. Some tricks Porsche used was to insulate the cylinder stud from the cooling air. Some 4-cam Carreras (587) and 906-910 had fiberglass insulating sleeves over the studs. There was an attempt using plastic/epoxy insulation. Some (930) cylinders had the stud encapsulated within the cylinder. The point was to shield the stud from the cooling air and have it heated from the case and head.
The other issue is the overall engine air cooling. Keeping the cylinder and head cooler definitely helps solve the head stud problem. That is best done with the 1.82:1 fan ratio.
ďFan drive ratioĒ:
Engine Fan Drive Ratio
This is a very worthwhile mod and additionally improves the performance of the A/C and heater/defrosters. On a hot day there is a net horsepower gain.


Iím curious, how much material was taken off the case halves to be able to bore the main bearing webs to standard? Did you need to resurface the cylinder seats in the case?

Best,
Grady
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Old 10-20-2004, 10:01 AM
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don't have the case back yet, i should know more about the amounts they removed from the case halves, Peter Frans had his done, and they removed about 0.1 mm from the halves , loosing about 0.05 mm deck height, which should still work for valve clearance

if not , i've been told i could simply use 2 cyllinder base gaskets

as for cooling, i allready ditched the heater in my car, so all that air will go over my Cyllinders, also a new shroud, the old one was cracked and full of holes... ceramic coated headers so those won't radiate heat... the fan ratio... cooling wise, i think the engine will get all i can think off

the studs, it's not as visible in the pic , but all studs have somthing around the stud hole, and it's in an ever so slightly different shade
so i'll take my chances on them, i seriously don't wanna remove something that seems ok... one of the few things that actually hadn't gone south on mine
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Old 10-20-2004, 10:22 AM
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Another option you might consider is using your old biral cylinders. You can have them bored/honed to oversize and get new pistons. You of course should find the pistons first! This might be cheaper than buying new P/C set and would keep you with steel sleeves to assure long case life. If you are going to do new P/C set then I agree with Grady about the 2.7 conversion. The engine will look exactly the same and have so much better power/torque. It looks to me from you're picture like you have time certs installed. I would think that the shop that did your machine work should be able to confirm this.

-Andy
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Old 10-20-2004, 11:03 AM
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Stijn

The 'head stud' pulling problem really started with the 2.7 74 US Motors (you'll notice that 2.7RS Carreras didn't really have this problem). I'm of the opinion that it had more to do with the additional exhaust requirements in the US (causing higher op temperatures) than just changing to Nikasil.

Nikasil is far superior to Biral in wear and frictional characteristics, What year is your car? you say 73 but I would have expected a 7R not 5R case. I see you have pistion
squirters installed, what make are the nikasils?

Either way if you want to keep the original 2.4 displacement
I'd not fear using nikasils (also re-attach the heater!)

If it is a true '73S I'd be reluctant to take it out to 2.7 it is
the best and most valuable (next to a 73RS) early road going
911 and it would be a shame to hot rod it

HTH

Neven
73 911E

Easiest way to check for inserts (if its not obvoius) would be take a stud out and use a magnet (the case is mag the insert steel)
Old 10-20-2004, 11:53 AM
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I don't know that we can say the 73 RS didn't have this problem. There were only 1500 or so built and they tend to not be driven much. I bet the ones that raced had timecerts or casesavers installed pretty early on in life.

The 74 would have no more reason for pulled studs than the 73 rs. The 74 had a normal early exhaust just like in 73. The thermal reactors weren't installed until 75 even in California.

-Andy
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Old 10-20-2004, 01:10 PM
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Andy

I may be wrong on the 74/75 Issue but as BA states it was the increased size, mag case, aluminium cylider combo that caused the head stud problem and since Porsche did not go to divalar studs until 77 I think it was the thermal reactors that finally broke the camels back

Either way 2.4 with case savers and nikasil is a fairly save bet, if you want more insurance change to a later or after market head stud

Neven
Old 10-20-2004, 01:37 PM
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Andy : don't have history on the car, dunno who did the previous work on that engine , or when they did anything, all i know is that the insides were pretty worn , need new camshafts , cylinders, case needed boring


Neven : my car ain't numbers matching , looked it up with porsche, but it's still an engine number that fits 2.4 engine displacement, and going 2.7 is a bit to far from "core originality" to my liking ( there's enough other , cosmetic stuff that won't be original, but i find ok )


i made up my mind, i'll go with 2.4S, and do whatever i can to cool it
i'm not going to track it, neither am i going to daily drive it or do long haul drives( 300 miles or more )...
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Old 10-21-2004, 02:08 AM
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Stijn

I find it interesting that people think they are looking after Porsches by not 'daily driving' or 'racing' them, They were not
built as museum pieces. Last weekend i went on a run to Taupo (300K from Auckland NZ) and one of the cars, also from auckland (which is used regularly by the owner) was a 1959 356 1600 Carrera GS, it wasn't pristine but in my opinion the best thing the owner does for the car is drive it

Neven
Old 10-21-2004, 02:34 AM
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Neven , i live exactly 1 mile from work
i'de damage it more with driving it ice cold , then by keeping it for saturdays, sundays or other off work days

if i lived a little bit further from work, and didn't live in an appartment block without garages. ( it's a targa, yes it leaks, and street ain't safe around here to park anyway ) you can bet i would daily drive it...

mind you, when i do drive, maybe i'm not tracking it , but i will redline everytime i drive it , i just love the sound of the beast in the back
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Old 10-21-2004, 02:39 AM
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Nevin,

I agree with you that the thermal reactor cars are much more prone to head stud pulls. But as you state the thermal reactors were not listed as the reasons for the headstuds pulling. May be something like 100 percent of the thermal reactor cars pulled the studs while only 20 percent of non reactor cars pulled the studs. (I made those numbers up but the point is it's still a risk).

-Andy
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Old 10-21-2004, 10:19 PM
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Andy

Yes but had 2.7's been fitted with case savers ex factory the percentage may have been 1%

Neven
Old 10-21-2004, 10:34 PM
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Neven,

Point well taken. I have seen one pulled stud on this forum on a 2.7 with timecerts. It was a post from Wayne about using Casesavers instead of Timecerts. With Stijn's engine I think you are right and there is very little risk of pulled studs with the 2.4 nicacil cylinders.

I have my own little pet theory that we will start to see pulled studs on 2.7 engines with timecerts or even casesavers now that everyone is using steel studs instead of dilavar. I'm sure there will be much less than the original problem but enough to start being noticed in a few years. By the way I don't believe that the special studs (race ware, ARP, etc) will make any difference on this as they all are made of steel. The big question for me is will the stud pulls on mag cases with inserts approach the broken stud rates of Dilavar studs?

I used Dilavar studs on my 2.7 so you can guess which risk I think is greater.

-Andy
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Old 10-22-2004, 10:45 AM
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i ordered my Nikasils , should have them , along with my case and reconditioned heads in a week or 2... big dent in the budget , but no half measures on the engine...

small side question , is there any disadvantage if i start assembling in november, so i can get my case sealed, and a lot of parts out of the way... but do my engine start and run in a few months later?? say april?

or should i just gather all the parts, and only start assembling when i have everything to finish the job in one go?
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Old 10-25-2004, 01:06 AM
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just received the tally from the machine shop

case bored to original spec
oil bypass milled

heads reconditioned
new valve guides
new valve seats
new intake and exhaust valves

crankshaft micropolished
rods recontditioned and back to original spec on big-end and small-end

set of new 2.4 Nikasils

4700 euro's or about 5700 USD

guess i should have gotten me a less expensive hobby
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Old 10-29-2004, 05:50 AM
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Why not get 2.2S Nikasil pistons and cylinders? It's exactly the same diameter as 2.4 but with higher compression which will give you 10.3:1. Much better...
Old 10-31-2004, 11:08 AM
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i did consider it , but i'll keep it stock

also 2.2S will not yield 10.3:1 compression, it's well documented
it's something like 9.6:1
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Old 11-01-2004, 02:06 AM
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Hey Stijn,

Its time to update your signature..
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Old 11-01-2004, 01:43 PM
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