Porsche torque plates - Page 2

camgrinder · 01-09-2005, 02:24 PM

Can you bolt a cylinder, head and cam carrier on one half a block, and measure the cylinder with a dial bore guage from the crank side? If you could, and you see a distortion of a previously measured bare cylinder, you would know torque plates are worth it.

NevenM · 01-10-2005, 12:15 PM

Snowman

Did you torque plate as you bored? I'd not be surprised if Mahle do, someone posted

Quote:

New cylinders from Mahle are absolutely round

Which I know not to be true, my new biral cylinders were far from round. I have talked to some people who thought porsche cylinders were tapered but I think what they were measuring was the ovality at the bottom when the cylinder was in its relaxed state. The VW high perf engine builder I use torque plates before boring. I check to see if he bothers for honing but I can't see the point as the hone itself will cater for small variations.

When you run JE pistons in bored cylinders I assume they run at a wider clearance than Mahle ones so cylinder distortion is not so critical. It is often stated that this is possible due to the superior metallurgy of Mahles piston marerial and forging but considering that only S pistons are forged maybe its because they torque plate bore their cylinders?, 2.4E pistons are cast with a steel inserts to allow them to run tight clearances

Neven MacEwan
B E E&E

snowman · 02:08 PM

The forged pistons loose all that excess clearence when they get warm.

Honing as I am doing and what most perf engine builders do is the final part of boring, some even use the hone to do all the boring.
With a Hone like the Sunnun one shown in my photos, you can use many differen't grit stones. With the coarse stones you can bore the cylinder out 0.005" all the way to 0.150" if you want to (and have the time). Usually a boring bar is used to remove the gross ammount and then the hone is used to remove the last 0.010" to 0.003" depending on equipment and operator. Then the stones are replaced with a finer one and the bore finished to within say 0.001", the stone replaced with a finer one and the bore finished to 0.0005 to 0.0000" of the final bore. Then a plateau hone (a stiff brush used with silicone paste, or similar) may be used or a grape stype hone to put the proper final finish on the bore. No significant material is removed by this last step.

The torque plate isn't usually used with the boring bar because the bore isn't close enough to the final size to make any difference. In the case of someone trying to speed up the process or lacking a really good hone they might use the boring bar to get the cylinder to within 0.002" of final size in which case the torque plate would be required for both operations. A boring bar cannot be used to get any closer because it leaves deep grooves that must be removed by a hone.

As to Porsche and stock cylinders. On an all out race car, the pistons are usually not stock nor are the cylinders. But even a stock cylinder may benefit from a touch up honing with a torque plate. I have done this and it took one or two thousands off some spots of the bore, making a "new, round under torque" hole. Given the way Porsche cylinders are made the fact I even honed the cylinder is conterversial. But the fact that torque plates work is independant of this.

As to Mahle pistons, I think they are WAY overpriced. They are excellent pistons, but are they really any better than any QUALITY modern hypereutectic piston that sells for $25 ea. for a productin car?

NevenM · 01-10-2005, 02:14 PM

Jack

I'll have to disagree with you here (and I know how dangerous that is!) A boring bar cuts and a hone grinds so by not torque plating during boring you are boring a cylinder in its relaxed state, you then are honing with it torque plated to correct this which it will do to some extent but as the hone removes material from a surface it will also 'follow' the existing cylinder profile (which will not be perfectly cylindrical as it was bored unstressed)

I also am of the opinion that this is far more critical in an air cooled cylinder where the bore does not have as much support as a water cooled engine. This is where the practice of torque plating may differ from high perf V8s to aircooled. In a watercooled situation you are correcting for a minor amount of upper cylnder distortion caused by the strain of the head studs but the whole cylinder is under strain in a porsche motor

Neven

mpdevelopment · 01-10-2005, 02:42 PM

[QUOTE]Originally posted by NevenM
[B]Snowman

Which I know not to be true, my new biral cylinders were far from round.

How much out of round? All the new sets I have checked biral or aluminum (nikasil,alusil) measured round to within .0002".

snowman · 05:04 PM

NevenM,

Never worry about disagreements with me, although I did hear rumor that Pearls before Swines, Rats, cockroach might have been based on my life. That said,

Grinding is usually better than cutting (for final operation) in my opinion. Take for example valves, would you rather grind or cut the final finish? So as long as there is enough material left for the hone to completely establish a cut, say approx 0.015" to 0.010" you will end up with a perfactly round (under compression) cylinder. I have checked using a dial bore guage, with the torque plates still attached and the roundness is perfact within 0.00005" and the taper is within 0.0005" (pretty darn good).

NevenM · 01-10-2005, 05:01 PM

Quote:

Grinding is always better than cutting in my opinion

This depends, grinding as in facing valves or a surface grinder yes, where the grinder is 'fixed' and the wear of the abrasive is much less than the workpiece but a hone (afaik)
is not fixed but is pressed with a constant force against the workface, ie theoretically it removes a relative amount of material not an absolute amount

Neven

911pcars · 01-10-2005, 05:05 PM

Honing tools can be flexible or rigid. I think Jack refers to a rigid hone (Sunnen) that removes equal amounts of material from round holes.

Sherwood

NevenM · 01-10-2005, 05:05 PM

Jack

Your results are impressive. What torque do you use on your torque plate? and have you measured them in their relaxed state?

Neven

NevenM · 01-10-2005, 05:07 PM

Sherwood

Thanks for that, I was speaking drivel then :-)

Neven

NevenM · 01-10-2005, 05:38 PM

Jack

Your results are impressive. What torque do you use on your torque plate? and have you measured them in their relaxed state?

Neven

snowman · 01-10-2005, 05:41 PM

I use the same torque as the actual head bolts (studs) will use. As for the 912 cylinders I have measured them relaxed, and in increments of 10 ft lb torque up to 40 ft lb. They are ALL OVER the place, you have to do one to understand, but its scary. They constantly change and by numbers like 0.005" to 0.010". But they do repeat. Both same and seperate cylinders.

Std Porsche cylinders for 911's are much better, more like 0.002" numbers. But even thats a lot considering running clearence hot should be very very small.

NevenM · 01-10-2005, 05:52 PM

Jack

Have you considered calculating the 'effective' strain that a cylinder is under at running temp and torquing to that. It would be a function of the exp rates/temp diff/x section/modulus between cylinder and stud, Alu/nikasil cylinders would be under considerably more than cast/iron/biral (they did pull/snap studs after all), either way it would be higher than cold

Neven

snowman · 01-10-2005, 06:16 PM

Nice things about 912 and cast iron cylinders, they match the studs much better.

NevenM · 01-10-2005, 06:19 PM

Quote:

Nice things about 912 and cast iron cylinders, they match the studs much better.

Yes in expansion rate but not necesarilly in operating temperature, Also I assume birals act more like cast iron than Ali

Neven

snowman · 01-11-2005, 10:19 PM

Quote:

Originally posted by aigel
Snowman:

I ... Most shops that build engines around here would not offer a rebore at all. I can see where they are coming from. If it comes from Mahle, it is new, fits out of the box and makes a warranty on the builders work much easier.

Cheers, George

Thats absolutely TRUE! Why? common sense, if you can make all the money you want at little or no risk, can offer a small ammount of BS to tell the customer how good you are and how much better his stuff is than everyone elses (even though it is EXACTLY the same as everyone elses) and as most Porsche drivers don't road race each other daily or ever, and in fact most Porsche owners are left over Z car owners, if you know what I mean, then why should they do anything else?

However on this board WE are a cut above the common riff raff (of course) and therefore looking for some REAL performance enhancements.

Consequently we talk about stuff that may offer some kind of real advantage when we get on the track. And then there those who follow this stuff and know more about it than those of us who actually do it. Its a respectable hobbie and in the end adds to the sport, so they are also welcome. As the the Z car stereo types, please go find a used Z car somewhere. As to all of my race car groupies, all 3 or you, see you at the races.

germansupply · 01-22-2005, 12:36 PM

snowman,

i do not wish to hijack your topic. i have been researching cylinder honing on behalf of our machine shop and found your thread. he requested me to do some web research, as he is not web friendly.

we are attempting to hone 914 94mm cast iron cylinders to 96mm. we have constructed a boring fixture similar to the one in your photos, but we are using an engine case for the "receiver" and a steel torque plate on top.

what is happening is that the bottom of the bore is "coning" by about .003-005", he cannot get the bore to stay dead true at the bottom. is there anything you can think of that will prevent this?

350HP930 · 01-22-2005, 01:53 PM

If you mean that your honed hole is tapering out at the bottom then try a combination of reducing hone pressure and how far you overstroke the cylinder at the bottom.

germansupply · 01-22-2005, 02:05 PM

350HP,

yes, the hole is tapering at the very bottom. the cylinder wall is quite thin in this area. reducing the honing pressure makes total sense to me.

Quote:

Originally posted by 350HP930
... and how far you overstroke the cylinder at the bottom.

i am sorry to sound ignorant, but what do you mean by overstroke?

350HP930 · 01-22-2005, 02:29 PM

To properly hone a cylinder the hone's abrasives stroke slightly out of the cylinder, usually by a fraction of an inch. This is referred to as overstroke and the more it hangs out the greater the abrasive force on that particular area of the cylinder is. This occurs because the honing head is applying the same force over a smaller area of the cylinder wall. Depending on the design of the honing head this problem may even be aggravated if the abrasive pads attempt to tilt outwards when they overhang the bottom of the cylinder.

I don't think its due to the thickness of the cylinder since if it was stretching it should result in an undersized bore since the cylinder would be under less load than the rigid portions of the cylinder so I believe your problem is more likely due to the extra loading and possible abrasive orientation issues during the overstroke.

I suggest less pressure since its likely to reduce the problems caused by the overstroke and is a good general cure for taper and hourglass problems that occur during the hone process.