QSC cylinders - problem fitting

CruiseControl · 02:59 AM

While I am waiting for parts to be returned from the machinist, I tried fitting the new QSC cylinders to the case with new 933 fully threaded dilavar head studs.

The cylinder(s) require to much tapping and still 40m (1.5") from final position. Tried the QSC cylinder on another 2 positions (5 and 6) and the same story. Tried another QSC cylinder and similar varying results.

The next step was to try one of the old Mahles. I nice slip fit over all three locations, hence not the studs being the problem. If I had used the Supertec or Raceware studs I don't think the problem would exist as these two studs have a reduced diameter over the center section of the bolts.

I measured the hole diameter and the QSC are about 10.5mm dia and the Mahles at 10.2mm.

It would appear that a Chinese CNC machine has been used for drilling the holes for the head studs, or even worse a Black and Decker.

As I see it there are two choices:
1. Scrap the 993 studs and replace with Supertec of Raceware
2. Machine out the existing holes to at least 11mm or even 11.5mm may be required.

I would appreciate any advise from the experienced, not so the theory man.

Thanks
Paul

mb911 · mb911's Garage

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Steve@Rennsport · 12-02-2006, 10:25 AM

Paul:

I don't use QSC cylinders, but to me the inituitive "solution" here would be to use Supertec studs and thats what I'd recommend.

Personally, I would not machine the cylinders to suit.

MBEngineering · 10:46 AM

HI Paul, I wondered how long it would be before some one would shout about the fit of these cylinders, and you are having a little prob' with the cylinders NOT fitting over the studs, well you will need to pop a drill down the hole as changing the studs will not help, I have just built 2 engines with the same cylinders and had the same prob' and i was not using 993 studs, I was using supertec studs , that was on 1 set and on the other set the cylinder lining was prow-ed/sticking up above the head face and had to be trimmed back as the head would not sit on the cylinder flat . have fun .

regards mike

911pcars · 12-02-2006, 11:07 AM

Errr, perhaps the QSC cylinders aren't made correctly. What does the distributor/manufacturer say?

Sherwood

CruiseControl · 12-02-2006, 01:34 PM

Thanks Mike and Steve

Overnight response from two of the three experts that I was looking for is rather good. I would also like to hear Henry's comments on this.

At this stage it looks like the machinist is to be loaded with even more parts.

I would not try to fix a Chinese cylinder using my Chinese vertical drill stand.

Paul

cnavarro · 12-02-2006, 03:00 PM

In the long run it will be more expensive or the same price to machine the cylinders than to replace the studs, and in theory, you'll be better off with a set of upgraded studs. Sucks that a budget product requires additional expense to fit properly IMHO.

mb911 · mb911's Garage

so got me thinking . I just got back from the shop . I checked all 6 of my qsc 98mm from supertec and they all fit on the studs and in the spigots. I am using all stock steel studs(4 years old) and looks to be good. I ask only because I Feel this makes a difference. Did you buy them from supertec?? If so I would be suprised as he QC's every one of the cylinders to height match them and check them for roundness etc. but maybe not hole spacing????

as to wether Henry will answer this post I would highly doubt it. Not because he is scared but more that I think he has a sour taste in his mouth from the last few weeks happenings. so if I were you guys I would email him direct. He is a very stand up guy And will help how he can

I guess I would be concerned about oversizing the holes if that were the case maybe you could exchange one cylinder or 2 . Any how remember these are not mahle, nor NIKIES but a nice low budget alternative but with that comes some possibilitys of a little bit of "making it work" . but it does suck just like charles points out

CruiseControl · 10:30 PM

Charles: I would have loved to used your cylinders however the local Australia agent (in Victoria, Australia) failed to return with confirmed pricing. With budget costings of the QSC at less than half price, QSC was the decision.

This morning got a quality new 10.5mm twist drill and tried passing the shank end first through the head stud holds. In all instances the shank of the drill stops solid at a point about 1 to 3 fins up from the case side of the cylinder. Similar when addressing the drill from either end of the bolt hole.

Having a reasonable guide of the upper part of the hole I proceeded with the Chinese vertical drill and the 10.5mm twist drill. The result is I now have the QSC cylinders that have a nice fit over the studs.

It would appear that the cylinders were drilled at the factory from both sides, and a full 10.3mm - 10.5mm clearance hole was not achieved.

Charles: I would have loved to used your cylinders however the local Australia agent (in Victoria, Australia) failed to return with confirmed pricing. With budget costings of the QSC at less than half price, QSC was the decision.

This morning got a quality new 10.5mm twist drill and tried passing the shank end first through the head stud holds. In all instances the shank of the drill stops solid at a point about 1 to 3 fins up from the case side of the cylinder. Similar when addressing the drill from either end of the bolt hole.

Having a reasonable guide of the upper part of the hole I proceeded with the Chinese vertical drill and the 10.5mm twist drill. The result is I now have the QSC cylinders that have a nice fit over the studs.

It would appear that the cylinders were drilled at the factory from both sides, and a full 10.3mm - 10.5mm clearance hole was not achieved.

Charles, I value your opinions and sincerely apologies for not including you in the experienced/expert number count above.

Ben: The reputable porsche repair shop that I obtained the parts from in the US did check piston/ring/cylinder tolerances prior to shipping to Australia, as they outlined a long way to return. I did not get the cylinders directly from Henry.

Reference to the 993 dilavar studs, I gave my original parts requirement to a shop that is recognized on this board and when I questioned the 993 studs, I was assured these studs are OK and the selection of the studs being based upon pricing at the time.

Time will tell if there are savings in real terms.

Paul

mb911 · mb911's Garage

I suspect they will last along time. They look great to me and I have seen wild to mild on cylinders and they look pretty nice.. I am glad it has worked out for you

cnavarro · 12-02-2006, 05:13 PM

No problem here Paul, I'm just glad that you got them to fit and the problem is resolved to your statisfaction. I should have noticed you are over in Australia. Indeed just redrilling them would be the most cost effective solution, since the studs once you factored in conversion rates and shipping would have been even more.

Henry Schmidt · Henry Schmidt's Garage

The problem with head stud fitment as it pertains to QSC cylinders seems to be the coating applied to the cylinders.
It seems to add an inconsistent layer and this sometimes causes problem.
This is easy to remedy. Run a drill (10.5 to 11mm) through the holes and you're good to go.
A hand drill works fine.

CruiseControl · 12-03-2006, 05:02 PM

Henry:
Thanks for your response, much appreciated.
Have done this with 10.5mm drill and all fits OK.

Am one of the 99.9% that value your contributions, 99.9% of the time without question. Let's not concern ourselves with the remaining 0.1

Thanks again
Paul

sand_man · 12-04-2006, 07:44 AM

FWIW, I used 98MM QSC cylinders sourced from Henry for my 930 engine rebuild and had no troubles whatsoever with fitment over my new ARP headstuds. In addition, after close to 5,000 miles, they are holding up fine. One of these days, I'll do a hot leakdown and compression test just to check on things.

Lukesportsman · 12-04-2006, 04:01 PM

With all the negative views on JE's and Mahles, Do the QSC's have less piston slap? Or a better way maybe to ask this is do the QSC's thermal expansion rate match the JE's better than Mahls?

I'm not highjacking, I hope, since the solution has been completed.

Henry Schmidt · Henry Schmidt's Garage

If the JEs (pistons) are properly matched to the cylinder there is no piston slap issue with JEs.

Just like Mahle, pistons must be mated to the cylinder they are going into.

This is the job of the engine tech. I would assume that most piston slap stories with regards to JEs are either old stories which have no bearing on modern JEs or misfit pistons. JE will build a piston to suit your cylinder size.
Because Mahle cylinders come in 4 different size groups for each diameter spec you would need 4 different JEs to suit all those sizes. Most engine builders just build what they are supplied with.
JEs makes a generic piston (shelf) that is designed to fit a 0 Mahle in new condition. Imagine the clearance you might get if you put that shelf piston in a used #3 Mahle cylinder.
The clearance might be huge and that would not be the fault of the piston builder.
At this point JE is specifying .0015 clearance for their pistons for Nikasil cylinders. At .0015 " clearance there is no slap.

sand_man · 12-05-2006, 06:14 AM

Quote:

Originally posted by Lukesportsman
With all the negative views on JE's and Mahles, Do the QSC's have less piston slap? Or a better way maybe to ask this is do the QSC's thermal expansion rate match the JE's better than Mahls?

I'm not highjacking, I hope, since the solution has been completed.

Sorry I didn't see this question sooner. FWIW, I have no "slap" with my QSC and JE combo and that's due to what Henry explained about proper matching. It was through his care and attention to detail when I placed my order (through him) that mine are right.

Lukesportsman · 12-05-2006, 02:35 PM

Thank you for the responses.

I never understood why there is a belief that no one outside of Mahl can build Porsche pistons. Mahl also manufactors pistons for 72 Nova's too with their cast iron sbc. Its not like Al engines are unique today. Its also pretty certain that a Jaguar, LS1, B16, or 996 do not all share one specific rate of expansion. So why would the 911 be the car unable for piston manufactors to engineer!