Porsche torque plates - Page 3

germansupply · 01-22-2005, 03:12 PM

i will print and present these thoughts to my machinist and get back to the forum early next week. thanks for the input.

snowman · 01-26-2005, 08:16 PM

The mad rocket guy has some excellent comments. Also if your machinest has a hone like the one pictured ask the factory rep to pay you a visit. Reps can do more than sell stuff, they can get expert factory help with the tool, like the hone, and make it do the job you want it to do. Even though I often threaten salesmen with a shotgun, sometimes they do serve a purpose.

350HP930 · 01-26-2005, 08:24 PM

The past several months have intimately reaquainted me with the art of honing.

Fortunately it allowed me to work wonders when it came to reconditioning my 930 cylinders. I'm lucky that I landed a job in a shop that uses diamond abrasives.

germansupply · 01-26-2005, 09:34 PM

fellows,

i haven't the machine shop yet this week, but i plan to get there in the next day or 2.

yes the machine shop has a sunnen hone similar to the one in the photos. what i have to do is tread a fine line between "helping" him and insulting his professional abilities...if you catch my drift.

350HP930 · 01-26-2005, 09:40 PM

His abilities are already in question if he does not know how to hone a relatively straight and round hole.

germansupply · 01-26-2005, 09:53 PM

i know what you mean, but i am not so sure. the cylinders are very thin at the bottom (~.100) and i do not find it inconceiveable that this area would deflect enough during the honing process to cause an .003 taper. but i am not an expert.

350HP930 · 01-26-2005, 10:06 PM

Some cylinders are more difficult than others to hone, but trust me that any cylinder can be honed straight if its done by someone who knows what they are doing with a quality honing rig.

As an expert I can say that anyting more than a 0.0003" taper or out of round is sloppy work. Ten times that amount is egregious.

snowman · 09:22 PM

0.0003" taper is pretty darn good, most hope for 0.001" taper. even on race engines. However it goes out pretty quickly, ie more than 0.0015" taper isn't pretty good anymore, and 0.002" taper, forget it. Bottom line 0.0003" taper per inch of stroke is more like it. Torque plates affect this but in very complex ways. Bottom line, with a torque plate everything should be good.

Out of round is completely differen't. A hone will make a cylinder almost perfactly round, no way to measure the out or round, as its so small. But with a torque plate the ammount of out of round should be the same, ie nothing. If the torque plate is relased then the out of round may be pretty big.

As to the bottom of the cylinders, if the rings do not go there, don't be very concerned. At the bottom ot the stroke, there is nothing, ie no power, no anything, so who cares?

davidppp · 05-31-2006, 01:57 AM

Very interesting thread.

I have always assumed my cylinders will not be remotely round when hot and under the much higher clamping pressure which results from expansion of the hot hot cylinder, and head vs the not so hot stud...

I very much doubt that boring or honing with a torque plate can do much to make the cylinder approximate it running shape...

My limited experience only shows that running 4-6 thou piston/cyliner clearance works well for power...but is noisy and beats out the top ring grooves sooner..

Does anyone have any data for the actual temperature distribution in a 911 cylinder please..ideally in a race engine?

Kind regards
David

Steve@Rennsport · 05-31-2006, 11:24 PM

Hi David:

FWIW,....We've been boring Porsche cylinders using torque plates for 10+ years and IMHO, its worth the effort based on what I see on the dial bore guage,........

I cannot remember the exact differences anymore but the tops of the cylinders closest to the heads ran hotter than near the spigots and the lower sides (next to the exhaust ports) were hotter than the upper sides (facing the cooling blast from the fan).

davidppp · 06-01-2006, 07:58 AM

Thanks, Steve.

This is the sort of data which really helps..if for example the temeprature difference is uneven around the bore, its absolutley unavoidabley going to make the bore out of round..

Unless we bore and hone with the same temperature distribution of course..

Then, the pistons them selves are also going to have temperature gradients, across the dome..hotter at the exhaust side by far than the inlet which recives regular thraml shocks from the induces gas..

As I say, the racers quick and dirty solution is masses opf clearance..

Not optimum at all..

Kind regards
David

Steve@Rennsport · 06-01-2006, 09:44 AM

Hi David:

The water-cooled crowd understands the value of strict temperature & dimensional control during cylinder finishing operations by circulating 190-200 deg F water through the engine with torque plates bolted up in place.

Unfortunately, its not simple nor easy to blow large quantities of air over the case halves and cylinders with the honing machinery in place,......

One simply does the best you can do.

snowman · 06-01-2006, 02:01 PM

Torque plates improve performance, even without the temperature of the cylinder being simulated. I suspect that the torque plate causes much larger changes in the cylinder than the temperatue does. Like Steve says, you do the best you can do.

cnavarro · 06-01-2006, 03:11 PM

Quote:

I use the same torque as the actual head bolts (studs) will use.

Why not use stock studs or all thread, rather than a bolt? It makes a difference on the "stretch" factor of the studs, especially at the amount of torque you are using on the fasteners.

Quote:

As for the 912 cylinders I have measured them relaxed, and in increments of 10 ft lb torque up to 40 ft lb.

Why do you run such a high amount of torque? On the VWs and 914s I've seen running cast iron cylinders, even in race prep, need no more than 28-32lb/ft, the lower the better, as the head flexes with that much force. It might be that the dissimilar head stud lengths are a factor, but still a single head across two cylinders would flex and bend when heated, causing the very head leaks you are trying to prevent.

Quote:

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

I agree totally on those figures as far as the distortion is concerned. Back a few years ago we manufactured biral cylinders (aluminum fins that had a pressed in ductile iron sleeve). We manufactured a boring/torquing plate to bore and hone them since as the cylinders would heat up, even without a clamping load, they would go out of round. We even saw as bad as .020" ovality, requiring us to leave the bores very undersized. I didn't help that we ran quite a bit of interferance, as we wanted to ensure that the aluminum could not physically separate from the liner until >600F. Ring life was significantly better and the birals that were honed in a torque plate exhibited better (and more even) wear patterns than ones that were done static (without torque plates). It wasn't until years after we had stopped making them did we see the difference.

Using a torque plate on a cast iron cylinder is very different than say, on a set of Nickies. Nickies grow quite a bit more than even the factory aluminum barrels by design whereas with cast iron cylinders, they don't grow anywhere near as much, so actually heating them up vs. doing the bore and hone operation cold (only heat provided by the friction of the honing stones doing their work) doesn't really net a huge difference or benefit (one way or the other).

Honing (or boring the aluminum blanks) Nickies generates TONS of heat because of the very high thermal conductivity, which would make holding one temperature and level of expansion very difficult. They get hot fast and reject the heat even faster. If you were to do a set of Nickies honed with torque plates, you almost would have to heat them to roughly 300F (that's about the point where they stop expanding) and hold that exact temperature, to get anying out of the procedure. Those who haver re-honed their Nickies in torque plates in every occasion ended up with very poor leakdown figures (>70%) and rings that never would seat, ending up in a re-plate.

I know that the factory cast cylinders did have more silicon to reduce the amount of expansion, to be a better match to the hypereutetic cast/forged pistons. That's one reason why many people don't like JE's in cast AL cylinders because of the expansion differences. That's why we planned our alloy around the expansion of a JE piston.

By this same token, I recommend both COLD and HOT leakdown tests on an engine with Nickies and even go as far as to recommend verifying ring gaps COLD, say <32F. Nickies stop shrinking right below freezing. I'm running .001" total ring gaps on my 912 engine with Nickies, set at 28F. Did I mention that's with CHROME rings on nikasil :-). We've been running chrome rings (<20lbs tension) since 2000. It all has to do with expansion rates.

Long story short- cylinder with less expansion has more to gain from honing with torque plates than a cylinder with greater expansion.

afterburn 549 · 06-05-2006, 11:37 AM

I know you guys are light years ahead of me (being a amature engineer with weak math skills ) but as things warm up, get hotter and cool dwn all in the same race all most in the same instant (ever watch a EGT gauge ? pretty scary ?) it would seem that there compression value will be changing constantly....one would have to shoot for middle ground and be happy..??

snowman · 10:23 PM

I use the same values I torque the head "studs" or bolts (a loose definitin of studs) to. High values are needed for a race engine. If it don't remain clamped, it cycles, and if it cycles, it leaks, it breaks. The temp does do something, and its probably significant, but we cannot duplicate it in the shop, so we don't. But the torque plates still provide a significant atvantage.