New Mahl set, would you completely disassemble

[Lukesportsman]

I just purchased a set of full finned 91-92 930 P&C's. They came assembled with rings installed and pistons already installed into their specific cylinders.

Is it a regular practice to break these down or to run these as supplied from Mahle? These came with Porsche part numbers on the box and I wonder if this is how they are/were supplied to Porsche factory assembly lines. It would seem very odd for them to assemble the piston/ring/cylinder outside of spec. For one, why waste the labor. For two, why open yourself to liability of people using it in error if not intended.

Certainly, I can see professional builders charging big dollars and who's name and reputation rides on each build to do such in a build. Is it usually needed? Mahle is said to have quite high standards and quality control.

Would any of you not be able to sleep using the assemblies as supplied and simply hooking them up to the rods? Along with my questioning whether I can do better than Mahl in gapping the rings, but also the added risk in removing the rings to check and reinstalling them.

[afterburn 549]

As a thought. I would find it difficult to hang a piston on a rod with it 1/2 hanging out of the cyl. Not imposable, just difficult..........JMO

[Lukesportsman]

Sure, never tried it myself either. Why would've they packaged it this way? I've heard of guys pulling their Allusils (KS) this way in concerns with rings so I'd have to assume they reinstalled them some how

I don't know if I will be able to, but thought I'd ask for opinions. This may be the actual variable to prevent it. Still, if this is not possible do you remove all the rings and start over? This seems so redundant and I never knew they packaged as such. I figured I'd file to fit and put it together with marked (paired) piston and cylinder.

[afterburn 549]

Back in my old VW days Mahl shipped piston in cyl with rings installed, I always ended up pulling them apart.
It is almost a moot pt not to take them apart - the rest of the rebuild you will have to wonder........ verses popping the piston out check the gaps and locations hang the piston on the rod and boink the cyl dwn onto piston, now no worries. JMO

[ChrisBennet]

Originally posted by afterburn 549
As a thought. I would find it difficult to hang a piston on a rod with it 1/2 hanging out of the cyl. Not imposable, just difficult..........JMO

I've often assembled the P&C on the bench and installed them that way. I don't always do it that way but it's a toss up which one is easier.

If you do it on the bench you have a little more control getting the rings into the cylinder on the bench and little more difficulty getting the wrist pin clip in.

As for trusting Mahle, I've learned when it comes to these motors to "Trust No One, Measure Everything Yourself". Personally I'd disassemble and check them you shouldn't lose any sleep over it if you don't.
-Chris

[afterburn 549]

C.B.,thanks - I knew if we batted this around long enough someone with exp would pop in and settle it. I know for me I would pop them out and check like you said.....its a long way back wards once you have it up and running...big gamble ??

[Lukesportsman]

I figured that would be the answer. I just didn't expect them shipped that way and it really isn't much more work than I planned to do anyways. Since I wasn't familiar with this shipping method, I thought I'd ask. Very good...thanks

[Walt Fricke]

Well, the two brand new sets of Mahle Ps and Cs I've bought I just installed as is. Pulled the pistons out, rotated the rings so the gaps were where I wanted them, put them on the rods, and popped the cylinders (not even worrying about which came from which) on. Caused no problems. Of course, a sample of two isn't much.

I think it is up to you - you've identified the issues, and it is your risk.

If I were an engine builder by trade I would hope I would be very efficient in popping rings off, checking gaps, putting them back, maybe even miking the pistons or using a bore gauge on the cylinders, etc., on the off chance that a long time outfit like Mahle messed up.

But it is just not worth it for me doing my own engine.

Now when buying a set of new rings from Total Seal, or getting a replacement cylinder, things are different. But a whole new set from the OEM manufacturer?

My 2 cents.

Walt

[Lukesportsman]

I appreciate your input and experience, Walt. I don't doubt the above comments either and as a pro I would certainly do things differently if for pay and reputation. I'm still on the fence, but may roll the dice as you did. I've built several engines, but doubt that I'm any better than a average local machinist only that I might care a little more sense its mine.

Yes I was bitten once by trusting a as shipped part: $3600 heads with springs set at wrong height. Bounced and bent 14 valves at 7000 rpm. Over the nose the springs were fine but at seat less than 1/2 the spec'd rate (right spring, wrong installation). Cams and heads purchased from same builder......no longer use them

[ChrisBennet]

Weighing the pistons would be a good reason to take them apart...
-Chris

[Walt Fricke]

Well, what are the odds that a new set from Mahle are out of weight spec?

Of course, if you have a gram scale (and I do, because they are inexpensive now from office supply places) and want a closer balance than what Porsche accepted - that's different. And quick - pull from cylinders (which I would do anyway, since I don't use what I think of as Wayne's method, since I had not heard of that before I read his book) and weigh. Five minutes, maybe, to get out the scale, weigh, and write.

Of course if you found one way off - - - Hmmm - I'm going to weigh my new J&Es just for grins.

And if I had Luke's experience with what he no doubt had reason to believe was an experienced builder of heads, maybe I'd be doing more measuring. But where does it stop?

My favorite is the new fuel cell Steve Timmins bought from one of the fuel cell outfits. There are only a couple of these, and they have been around for quite a while. Took him forever to decide that his horrible problems warranted a look into the new cell. Turns out the pickup had been inserted on top of the foam, not down on the bottom.

Guess what I did with the cell I just bought (but really, it was because I was adding a second pickup -- but I sure checked closely for the one it came with).

Walt

[afterburn 549]

You know this is great exercise...but truly - how hard is it to pop them out ...... ????????????????????/ !!!!!!!!!!!! like your not all ready there ??

[Steve@Rennsport]

Luke:

One should take everything apart and check all the ring gaps at the very least as thats been SOP here for well over 30 years.

I always measure & confirm cylinder height and weigh each piston & pin as parts of the overall balancing process.

[MBruns]

Over the years I have seen a few with some of the rings lined up to broken rings, I would not want to risk that much work for just an hour or less to check end gaps, proper installation of rings etc... More often than not they are fine but.....

Mike Bruns JBRacing.com

[cstreit]

I still do it every time, cause it only takes one broken or out of spec ring to make me regret not doing it. ...but I haven't found a problem with a set yet.

[Lukesportsman]

I truly appreciate all the Builders taking time to answer my simplistic and amateur question. I will do as recommended and remove the rings and check end gaps, weigh the pistons and match pins to improve balance.

I wasn't so much trying to cut corners but rather looking at ways to reduce builder error if doing unnecessary steps. I was afraid this would be a thread that would get little foot traffic, so THANKS.

[euro911sc]

Luke,

as a side interest, if you ever want to sell the engine and you provide the buyer with a total measurement/spec sheet it might get you some extra $$ or even make the buy. It would certainly make me feel comfortable.

Also, when you wake up sweaty in the middle of the night... you know, from that nightmare where there are billows of white smoke spewing from the rear of your freshly put together car... (saw one at Sebring this past weekend... stinky) wondering if you did something or not, you can open your desk drawer and check your sheet and rest easily.

Best regards,

Michael