Holiday ride of shame

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Wil Mittelbach
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Re: Holiday ride of shame

#121 Post by Wil Mittelbach » Thu Nov 14, 2019 12:39 am

C J Murray wrote:
Wed Nov 13, 2019 8:49 am
I did a short tech session at the Ocean City NJ ECH where I covered the potential problems associated with building an engine. There are 2 basic issues, an engine where lack of attention to clearances causes self destruction or an engine with mismatched component choices that may run forever but always run poorly.

Clearances are pretty clear cut. When the factory built the engines they could rely on the dimensions being very close to correct and they could mostly just assemble the parts. I am sure they learned to double check certain clearances but they could build an engine very quickly, much more quickly than checking all the things we have to check today with our abused parts. Now everything must be checked carefully. As a side note, Porsche tested the completed engines and if they were sub-standard they were carefully rebuilt by experts in finding the problems, so they slapped them together quickly with virgin parts and in the rare case that the result is not good they go back and approach the engine carefully. We have to start with the latter approach.

Mismatched component choices are very common mistakes made by today's builders. There is a planning process. First be honest about how you drive and where you drive. Don't build a 7500rpm engine for 4500rpm driving. Even F1 and MotoGP engine builders detune their engines because they need broad power delivery to achieve the greatest average power within the rpm range used while racing.

Porsche thought that the S/S90/SC/912 cam was as radical as was sensible for street use. They had Mezger do a lot of work on the 616 engine which resulted in some beneficial changes along with the C cam which yielded a big improvement over the Super results. If he felt he could improve the S90 cam he would have done so.

Your cam has 11* more duration than the hot stock cam. That pushes your usable rpm range up at least 500rpm and it reduces power in the lower rpm range. The reason your cam was changed to 104* LC is to compensate for the excessive duration. Changing/tightening the LC closes the intake valve closer to the same point as the stock cam to try to retain some low end torque and the overlap promotes acceleration. That doesn't really work and it puts the exhaust valve very close to the piston.

The planning process is pretty simple, consider use requirements, choose cam, choose CR that matches cam, size carbs correctly to match the package. Because Porsche carburetors are so expensive and their appearance is important when originality is a factor then the plan for the engine could have the carb choice make the cam choice for you.

What carbs do you have? What CR will you have with the pistons and heads that you have? No guessing! Answer those questions and I will tell you what I think you should do.
++1

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Re: Holiday ride of shame

#122 Post by Mike Horton » Thu Nov 14, 2019 1:48 am

Dan, the next thing you'll need to know, is the combustion chamber volume, as that will determine what comes next. If the heads have been cut a lot, it will also effect the distance of the engine centerline, to the rocker arm plane, and the ability to correctly adjust the valve lash, and keep the adjusting screws positioned, to still pass oil through, the rocker arm geometry issue. The circular cut, vs the entire surface, may not be a serious issue, as long as the book dimensions, are maintained. The depth of the head spigot, from the combustion seating surface, to the top edge, is on the order of 10mm, required for het cylinder top, to seat correctly. Like C.J., contact me off post, and I'll try to help, if I can. There are several checks, you'll need to do, before starting to reassemble. I agree with C.J., and Will, on the above comment.

Do you have another set of uncut heads? Do you have another cam core, and what are the end markings, on the slotted end?
Mike

Dan Epperly
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Re: Holiday ride of shame

#123 Post by Dan Epperly » Thu Nov 14, 2019 12:46 pm

Mike Horton wrote:
Thu Nov 14, 2019 1:48 am
Dan, the next thing you'll need to know, is the combustion chamber volume, as that will determine what comes next. If the heads have been cut a lot, it will also effect the distance of the engine centerline, to the rocker arm plane, and the ability to correctly adjust the valve lash, and keep the adjusting screws positioned, to still pass oil through, the rocker arm geometry issue. The circular cut, vs the entire surface, may not be a serious issue, as long as the book dimensions, are maintained. The depth of the head spigot, from the combustion seating surface, to the top edge, is on the order of 10mm, required for het cylinder top, to seat correctly. Like C.J., contact me off post, and I'll try to help, if I can. There are several checks, you'll need to do, before starting to reassemble. I agree with C.J., and Will, on the above comment.

Do you have another set of uncut heads? Do you have another cam core, and what are the end markings, on the slotted end?
Mike, I have a stack of heads and cams if needed.
My plan is to get everything back from the machinists then dry assemble to see what I have using all the pieces provided and to report back.
I must say the engine ran great until it didn't. I had very good power across the band, it was responsive in town and on the freeway. It wasn't as zippy as my other B with a 912 cam, big bores and Solexes but it was good enough.

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Re: Holiday ride of shame

#124 Post by Mike Horton » Thu Nov 14, 2019 1:26 pm

" It wasn't as zippy as my other B with a 912 cam, big bores and Solexes but it was good enough."

A street sweet spot suggested by many, who've been at this a long time. Another favored combo, is the straight "C" set up, for reasons Cliff mentioned. Having learned the hard way, back with my first modified engine (late '60s, with low budget), a Normal, converted to Super, with a high duration Racer Brown "Speedster" race cam, stock small port heads, and S tuned Zeniths, I had a street engine which ran Great, from above 3000 RPM, to about 5000 RPM... see where this is going? I was happy with my first A T1 Normal, and in retrospect, would have been better off, restoring that N engine, in one of the best driving 356s I ever had, a T5B. I started with a 31,000 mile car, needing a crank repair.

As Cliff said, decide what you want/need, and assemble a total package, to get there... even the racers here, compromise, in their street engines, and wisely so,

Al has posted, the '63 B Normal, may give the best service ever, and Al believes what he says, based on about 107 years of experience.

The older I get (Birthday yesterday), the closer to original stock I seem to build my engines. this last one notwithstanding.
Mike

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Re: Holiday ride of shame

#125 Post by Mike Horton » Thu Nov 14, 2019 7:01 pm

Vic, Dick, Jacques, Harlan, Al, other "old timers" who were around when the old German Kolbenschmidt big bore kits were new;
Below is a pic, received today, from Rick Cool, another old 356er, now in a 912, of an 85.45 mm high domed big bore, already machined for what appears to me, to be the early 22* head angle for the through B heads, does this look right, to you? IIRC, the industrial P/Cs, as Vic stated, were 85mm, and flat topped, like a Normal, like the set I had. So, if Ray did this much machining, to the flat topped pistons, was that not likely, to continue in use, otherwise cut way too much in the combustion surface, earlier smaller chamber volume N heads? Could that be the chain of events, which has put Dan, in this dilemma? Are not these German 85.45 mm P/C, the original "big bore" sets, which the Japanese, and now, the Asians, have cloned, in 86mm?

Further, if he has other uncut heads, would it not be wise, for Dan to return to some semblance of an(Y) other standard configuration set of parts, in one of the combinations, which would afford Dan the level of performance, he needs, in a more conventional manner? Determining the accurate dome volume, of those Ray custom cut, might be a challenge.

Other's comments?
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Kolbenschmidt 356 Vintage Big Bore, 85.45, for 22 degree head angle.jpg
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C J Murray
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Re: Holiday ride of shame

#126 Post by C J Murray » Thu Nov 14, 2019 7:17 pm

I would do a careful evaluation of the parts that we have already discussed first. Do the angles match exactly? What is the CR at the correct piston to head clearance? Then we will know what is best, use what you have or move on to other parts.
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Ron LaDow
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Re: Holiday ride of shame

#127 Post by Ron LaDow » Fri Nov 15, 2019 12:58 am

Vic Skirmants wrote:
Tue Nov 12, 2019 7:19 pm
[...]
You will have to bolt a head onto the engine and fill the combustion chamber with fluid; Ron Ladow can tell you all about it and even supply some trick parts to make it easy. ONLY THEN will you know FOR SURE what your compression ratio is.
I appreciate the mention, but I'll disagree about a specific point:
file - Copy.jpg
file - Copy.jpg (10.51 KiB) Viewed 316 times
Suffice to say that bolting on a head with anything like a stock chamber and trying to empty it of air by filling the chamber with a liquid will not tell you the actual chamber volume. I've made this point before and got hooted down, but 'parts is parts', 'physics is physics' and while it's a 'downer', gravity always wins.
In order to 'burp' the chamber completely, the plug hole must be at the highest point at some set of coordinates in a 3-axis rotation of the cylinder/chamber. It NEVER is regardless of the hokey-poky you dance. That's what it's all about and here's why and how you can prove it to yourself.
Like any engine designer, the factory wanted the spark plug as close to center of the chamber as was possible for even combustion and shorter ignition lead, and they didn't want to do so by leaving a bunch of plug (male) threads out in the chamber; they extended the 'boss' in the chamber to the extent they could. While the extension is subtle, (that red circle tells you the extent of the 'boss') you can slice through the plug hole C/L in any rotation you please, and you will ALWAYS find a lower path around the plug hole on one side or the other. No, I have not done so, but suffice to say I'm confident of the truth of that statement both because I'm pretty good at 3d visualization and the following.
Here's how to prove it: In order for the plug hole to be the highest point in 'burping' the chamber, right-side-up, it must be the lowest point while upside-down, such that you can drain the chamber dry of liquid THROUGH THE PLUG HOLE while holding it upside-down and rotating it through any 3-axis motion you try.
Assuming you have not drastically reshaped the chamber and are therefore using a shorter plug (meaning more ignition advance), or that you're not 'shaking' it, or trying some other tricks, you cannot do so. You can fasten a cylinder onto the head if you really want to test the limits of the rotation, but it won't matter; you will still NOT be able to drain the chamber through the plug hole.
How much air is left in that chamber/how mistaken is your data is a mystery to you (and me), but it is mistaken; stock chambers are as-cast and not anywhere near uniform in shape, let alone volume. Further, you have no real idea how far off one cylinder is from the other.
You may choose to build to such tolerances that a couple of CCs here and there aren't of concern, but be aware that none of the cylinders in your engine are of a C/R as determined by that method.
Ron LaDow
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Vic Skirmants
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Re: Holiday ride of shame

#128 Post by Vic Skirmants » Fri Nov 15, 2019 9:13 am

I really don't worry about draining the chamber through the plug hole. Since my method is to be sure the piston is all the way to the top, then go around the piston edge with some grease to prevent leakage. After checking, I unbolt the head, with a drain pan underneath. You have to remove the head to wipe out the grease anyway.
I understand your argument, but since most of my CC checking is on my race heads, which are pretty much modified in the chamber, I am confident of my numbers; on MY race heads.

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Re: Holiday ride of shame

#129 Post by C J Murray » Fri Nov 15, 2019 10:07 am

I have one of Ron's spiffy tools but I don't always use it. Ron, a slight redesign would have you selling more of those. Add an additional position to accommodate the 91mm cylinders. A larger bore with a step down to the 86mm size and a listing of separate default volumes would allow your tool to work on all of our engines.

So the alternative method for accurate measurement is to place a cylinder, piston, ring assembly on the work bench and place the clear plastic disc with burette hole over the piston and push the piston down until the top of the dome is level with the top of the cylinder. Grease seal the rings and disc and measure the volume with the burette. Now place a piston onto a connecting rod on an assembled bottom end. Place the piston at TDC and measure how high the top of the piston is relative to the top of the cylinder. Calculate the volume of that much height of your cylinder and subtract that number from the previous number. Now you know the volume to subtract from your head chamber number so that you can calculate CR. This is easy and accurate. Dan could do this with his old good cylinder and just get his TDC dome position number by positioning the piston at the top of the piston ring wear marks. That would be close enough, not perfect but very close.
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Re: Holiday ride of shame

#130 Post by Ron LaDow » Sat Nov 16, 2019 2:09 am

Cliff, that seems to be about as good as you can get if you are not really serious about the data.
Assuming you measure a piston with a flat top surface at TDC and do so normal to the pin C/L, and keep the piston from rocking to avoid those errors, you should get close. Certainly better than 'burping' cylinders with heads fitted.
The Pre Mat Top End tool did get a rev the other way; I got gripes that stock bores were ignored, so the caliper measuring hole got enlarged to measure the smaller pistons.
Got a dim for the larger cylinder ODs? If not, I'm sure Charles (my buddy at the Lit Meet) will give 'em to me.
And thanks. No reason that tool shouldn't fit all the cylinders.
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Re: Holiday ride of shame

#131 Post by C J Murray » Sat Nov 16, 2019 2:30 pm

Make your own caption...
Screen Shot 2019-11-16 at 1.23.54 PM.png
Screen Shot 2019-11-16 at 1.23.54 PM.png (1.61 MiB) Viewed 199 times
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Re: Holiday ride of shame

#132 Post by Mike Horton » Sun Nov 17, 2019 12:50 am

C J Murray wrote:
Sat Nov 16, 2019 2:30 pm
Make your own caption...
Screen Shot 2019-11-16 at 1.23.54 PM.png
… Porsche 356 nuts, armed and dangerous...

(or did you mean the character in the photo?)
Mike

Martin Benade
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Re: Holiday ride of shame

#133 Post by Martin Benade » Sun Nov 17, 2019 12:58 am

Those are some loooong spark plugs!

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