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1200 with a W100 cam, no big bore kit, will it work?
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russell
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PostPosted: Mon Nov 17, 2008 12:47 am    Post subject: 1200 with a W100 cam, no big bore kit, will it work? Reply with quote

been searching samba and couldn't find anyone thats done it without the big bore kit SO figured i'd ask

OK, so i decided to do a complete rebuild of my 1200, well once i split the case i found that the cam that is in it is almost the same size as my W100 iskendarian cam that i have in my extra parts. i measured the lobe sizes with a micrometer and the lobes are exactly the same height, just the W100 is alittle more narrow of a lobe than the cam that was in the motor, but its a very small difference, i've put it in the case with the crank, matched the dots and everything and it doesn't even come close to interfering with anything.
Now i've read that a few of you guys have done the "big bore kit" with the 83mm pistons, but i don't really want to do that, i would just kind of like to use my isky cam, but would like to know if it is plausible before i put it in and find out its gonna not run right and its just gonna cause a bunch of problems all this. i DO have the ratio rockers that were used with this cam that was used in my other motor (2180), i believe the ratio rockers are 1.25's if that helps, i also have a couple extra carbs lying around if the carb increase would need to be done as well (30 and a 34)
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glutamodo Premium Member
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PostPosted: Tue Nov 18, 2008 3:25 pm    Post subject: Reply with quote

If it's just a cam you want to throw in there, I personally would not do it. The heads and intake manifold are small on that engine, plus you want to keep it small displacement. I doubt you'd get much if any difference except maybe poorer running at low RPMs with just the cam. The cam works together with the rest of the intake and exhaust system, and the rest of that system is not designed for performance.

Since you are talking about big-bores, I'm assuming your 1200 is a 40HP and not a 36HP.... On a 40HP, if you reworked the heads - or put 1300 heads on there (ideal would be the European 1300 dual port heads) and used small dual carbs, eliminating the small intake manifold, and maybe a header, then a cam might help, but if you're just keeping the rest of the engine stock, I would stay with the stock cam.

How are your cam "bearing" bores, by the way? I've seen some pretty hammered ones on those 65/older no-bearing engines.

While talking about cams in a 40HP, I'll mention this:
If this engine has the original thin-head lifters, and you put in modern thicker headed ones, stock cam or otherwise, make sure there's enough room for those lifters to clear:

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volksworker
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PostPosted: Sun Nov 30, 2008 10:24 pm    Post subject: Reply with quote

All sound advice but the VW stock valve timing is so conservative that you will get a noticeable improvement with a 100. With a header, a larger main jet and maybe a little venturi modification or a 30 pict you will definitely make some more power. Do that with a 1385 kit and you will eventually break a crankshaft.........but with stock bore I wouldnt worry too much. I say do it............and Ive done it.
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PostPosted: Wed Dec 03, 2008 10:31 pm    Post subject: Reply with quote

volksworker wrote:
All sound advice but the VW stock valve timing is so conservative that you will get a noticeable improvement with a 100. With a header, a larger main jet and maybe a little venturi modification or a 30 pict you will definitely make some more power. Do that with a 1385 kit and you will eventually break a crankshaft.........but with stock bore I wouldnt worry too much. I say do it............and Ive done it.


Do explain how the crank would break. I would like to know. i have heard of this from several on here, never had it happen to me. and formulas vee 40's with stock crank, spin 7k all nite long at the races. and the cranks never break. no counterweights, simply balanced.
That crank has such a short throw, i dont see how you could even get it to flex. id guess 83's weigh a tad more, a lil trimming and im sure they weigh the same as the 77s. dont even know why im speculating, i need to simply go weigh them, i have both downstairs.
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volksworker
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PostPosted: Wed Dec 03, 2008 11:04 pm    Post subject: Reply with quote

Yeah , its a common problem with the 40hp crank and the big bore kit, they always break right at the same place, at the thin part toward the front. Stock 40s will do it also as Everett has said happened to him. Judson did a study and found that the cranks were forged at too low a temperature. There is lots of crank flex in a 40 hp crank despite its short stature, the 36hp crank is way worse and needs to be shotpeened or cryoed to turn higher than 3800 revs. Its a fatigue type failure from crank flex...starts as a tiny surface anomaly and develops into a crack. You can see how they fixed it with a 1600 crank placed side by side which of course rarely ever breaks. We shotpeened our formula vee cranks back in the day and they were perfectly balanced rotating assemblies which can help avoid this problem. Also I must say that I would still build a 40hp big bore but not expect it to live more than 40,000 miles if driven hard. I was just talking about it with someone today. The cool thing is that they still run after the break.......Ive driven a couple home that way. 40 horse with the late heads is a good motor.
Tom
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glutamodo Premium Member
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PostPosted: Thu Dec 04, 2008 9:29 am    Post subject: Reply with quote

volksworker wrote:
Yeah , its a common problem with the 40hp crank and the big bore kit, they always break right at the same place, toward the front.


Okay, I'm pretty sure the one 40 broken crank I saw, it broke right in the middle. It still did run OK though. Just with a PING-PING noise and way too much endplay on the crank pulley. I don't know how the lady that owned it drove the car though. Some time later on after the crank was replaced, the engine about died again, I guess a valve cover sprung a leak and about seized the engine from lack of oil.

In my 62, I got 90K out of a big-bore 40HP once, and the main reason rebuilit it at that time, was that I broke a ring.

I had a broken crank in a 1600 engine in my baja before too, which was right by the flywheel, but that's a different story.

-Andy
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John Moxon Premium Member
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PostPosted: Thu Dec 04, 2008 11:04 am    Post subject: Reply with quote

volksworker wrote:
Judson did a study and found that the cranks were forged at too low a temperature. There is lots of crank flex in a 40 hp crank despite its short stature, the 36hp crank is way worse and needs to be shotpeened or cryoed to turn higher than 3800 revs.


Obviously the study by Judson was carried out to allay fears of potential customers scared off by VW dealers who suggested they'd break a crank as soon as the fitted a supercharger.

Part of their findings was "cranks forged at too low a temperature" but mostly cranks broke when habitually overreved. Judson Instructions always carried a note to make the gear changes on the supercharged car at all the recommended stock speeds.

You might think then why bother if you can't overrev a supercharged car. The answer is supercharging isn't about revving the engine faster it's about more torque through more efficient filling and combustion.

In my experience breaking cranks on a supercharged engine has never been an issue...36 or 40hp.

...as for other methods of improving performance, it depends how you extract that performance.
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