Pics of a Duetto racer buildup - Page 38 - Alfa Romeo Bulletin Board & Forums
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post #556 of 764 (permalink) Old 02-05-2015, 06:18 PM
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Sometimes I think you just enjoy using all your neat machines! I really enjoy all the top-rate work you are doing!

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post #557 of 764 (permalink) Old 02-05-2015, 07:09 PM Thread Starter
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Thanks, Robert. I think I'm stuck somewhere between "Necessity is the mother of invention" and "Idle hands are a devil's workshop."

I've been reading up on plastics, trying to decide on what to use for the yoke's liners. Acetal (Delrin) is very tough, but UHMW (ultra high molecular weight) plastic is very slippery. A lower coefficient of friction is highly desirable in a sliding block set up, whose weak point was the binding of the bronze block against the yoke's steel wear plates. So I went ahead with slippery UHMW, and if it eventually disintegrates, I'll switch to Delrin.
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post #558 of 764 (permalink) Old 02-05-2015, 07:43 PM Thread Starter
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Hey, it's just about done! Still need to make the steel brace that limits fore/aft movement of the this assembly. I'm also going to mount the trailing arm directly to the chassis sheetmetal, so I'm not using the cross-piece that replaces the T-arm.
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post #559 of 764 (permalink) Old 02-06-2015, 05:48 AM
Richard Jemison
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Questions

Have you test assembled this stuf in the chassis to see if it has clearance for your components behing the diff to clear the chassis box behind the diff?

With the lowered roll center (not a good thing with this or a panhard or watts ) what spring rate are you going to use?

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post #560 of 764 (permalink) Old 02-06-2015, 06:00 AM
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Is your mill the one that attaches to the 9.8.5 x 16 bench lathe? I have that lathe and have been thinking about getting one. How do you like it and would you buy another one? I've been able to do so many things with my lathe a mill could do so much more. Thanks for the great documentation of your top notch work!

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post #561 of 764 (permalink) Old 02-06-2015, 12:26 PM
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With the lowered roll center (not a good thing with this or a panhard or watts ) what spring rate are you going to use?
Why do you say this?

Pete

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post #562 of 764 (permalink) Old 02-06-2015, 04:09 PM Thread Starter
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Is your mill the one that attaches to the 9.8.5 x 16 bench lathe? I have that lathe and have been thinking about getting one. How do you like it and would you buy another one? I've been able to do so many things with my lathe a mill could do so much more. Thanks for the great documentation of your top notch work!
Glad you're enjoying the thread, Gigem. Both my lathe and mill are stand-alone units. I like them, but if I had the space, I'd get bigger machines.

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Have you test assembled this stuf in the chassis to see if it has clearance for your components behing the diff to clear the chassis box behind the diff?...
No, I haven't test-fitted anything yet, Richard. Currently, this is a faith-based project, and there will be praying involved before I wiggle under the car with sliding block pieces in hand. And I'm not even religious. Then again, do you think a pesky issue like obstructive sheet metal would ever stop builders like you and I?

Like the underrated Vanilla Ice once said: "If there's a problem, I'll solve it. (Check out the hook while my D.J. revolves it.)"

69 Spider, 2L, street; pursuit of happiness
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post #563 of 764 (permalink) Old 02-06-2015, 04:19 PM Thread Starter
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I found a few more H.P.

Speaking of problems, I had to take a break from the sliding block project to address an issue I found with my intake manifold. I had disassembled it to have my local head builder match the intake to the new spare head being built, and I discovered that it was undersized for my Weber 45 carbs. I don't know why I didn't notice this when I had the whole thing apart for "carburetor madness" last year.

Below are pics showing the size discrepancy behind the mounting blocks (see that big step?), how much material had to be removed as scribed by the blue layout ink, and finally a comparo between intake matched and unmatched orifices.
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post #564 of 764 (permalink) Old 02-06-2015, 04:26 PM Thread Starter
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...With the lowered roll center (not a good thing with this or a panhard or watts ) what spring rate are you going to use?
I'm curious about this problem with the lowered roll center as well.

For rear spring rates, see my previous comment about faith-based race car development. If the race gods aren't listening to my prayers, at least rear springs are relatively cheap and easy to swap out.

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post #565 of 764 (permalink) Old 02-06-2015, 05:20 PM
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I suspect it's just a typo from RJ.

The stock Alfa has a low roll center in front, which sometimes goes below the ground when the car is lowered. (This can be cured using the dropped spindles RJ makes). In the rear, the roll center is defined by the trunion pivot, which is pretty high. Overall, the car has a roll axis (the line connecting front and rear roll centers) that tilts steeply from front to back. On hard cornering, this transfers excessive weight to the outside front, as we all know, as well as lifting the inside rear. The sliding block, watts, or panhard links used in the rear all significantly lower the rear roll center.

The roll axis still tilts down, but much less, reducing the weight transfer and notably improving the car's handling.

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post #566 of 764 (permalink) Old 02-07-2015, 09:26 PM Thread Starter
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Having never before had the occasion to remove the rubber isolator blocks from the intake manifold, I now discover that there were no gaskets between them and the manifold. What the H is going on here?!

I didn't have any extra gaskets on hand, and didn't want to delay reassembly to order parts, so I made some of my own. I had material left over from a sheet of custom-cut gasket for one of my race bike's engine side covers. I had that done about 10 years ago, but I never throw anything away. I used a carburetor gasket as a stencil.

While on the subject of gaskets, here's my experience using a gasket adhesive: Back when I reattached the intake manifold after the last time I melted the head (a year and a half ago), I used Gaskacinch adhesive to glue the gasket, both sides, between the intake manifold and the head. So when it came time to remove that manifold, it turned into a herculean task. There was a big freakin' Snap-On screwdriver, cheapass Harbor Freight prybar, and a lot of cursing involved. I really feared that I might crack the thing before taking it off. Even though it's a weak adhesive, there's a lot of surface area on that manifold to hold the glue, and it held on strong. I won't be gluing it together like that again. I wonder if the silicon-based gasket makers (Permatex) would be any worse.

Anyhoo, back to making gaskets. I can think of better things to do on a Saturday evening, but with a glass of cheap cab and in the company of my family, this was a satisfying projectina nonetheless.
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post #567 of 764 (permalink) Old 02-07-2015, 09:57 PM
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Quote:
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Thanks, Robert. I think I'm stuck somewhere between "Necessity is the mother of invention" and "Idle hands are a devil's workshop."

I've been reading up on plastics, trying to decide on what to use for the yoke's liners. Acetal (Delrin) is very tough, but UHMW (ultra high molecular weight) plastic is very slippery. A lower coefficient of friction is highly desirable in a sliding block set up, whose weak point was the binding of the bronze block against the yoke's steel wear plates. So I went ahead with slippery UHMW, and if it eventually disintegrates, I'll switch to Delrin.
Try impregnated cast nylon color is dark green very tuff but not brittle we use it in offroad racing as suspension bushings on said parts.
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post #568 of 764 (permalink) Old 02-08-2015, 12:05 AM Thread Starter
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Try impregnated cast nylon color is dark green very tuff but not brittle we use it in offroad racing as suspension bushings on said parts.
You're using Nyloil? Interesting. I like its properties, but it's very expensive to get a piece thick enough for a 30 mm wide block. But getting it as cheaper thin sheets for the yoke's wear plates is an idea...

69 Spider, 2L, street; pursuit of happiness
69 Spider, 1.8L, race; happiness of pursuit
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post #569 of 764 (permalink) Old 02-08-2015, 12:53 AM
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I've used PETP in the past and this is pretty hard wearing, as well as slippery, but there are other options out there now which are made to specific blends such as this Nylatron. I have always bought small rods and blocks of surplus stock, so I don't know what full retail prices would be nowadays.

BTW, is there not another way of bonding the liner onto the cast aluminium? I don't much like the thought of the heads of the machine screws snagging on the block when the inevitable wear happens.

Great project ..........

Alex.

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post #570 of 764 (permalink) Old 02-08-2015, 12:02 PM
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I never use gasket sealant on the inlet manifold of any engine, unless I intend not to run a gasket at all.

Way too much sealant is used on this site, and others, when it is simply not required.
Pete

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