Engine rebuild - your advice please

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C J Murray
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Re: Engine rebuild - your advice please

#46 Post by C J Murray »

James Fitzsimons wrote: Tue Apr 16, 2024 6:54 am
C J Murray wrote: Mon Apr 15, 2024 4:21 pm Light flywheels are a PITA on the street. Likewise, heavy flywheels are not for racing. That is the practical answer so if you want to be a little sportier on the street don't go crazy lightening your flywheel.
Thanks for weighing in CJ. I guess what I'm not 100% clear on is what people generally consider to be "light". Is that anything less than stock? Is there a good compromise that people think is reasonable for a street engine but gives that slightly sportier performance?

I realise this is an "it depends" kinda question, but as someone who has only driven a car with a stock flywheel (and not for a long time) I'd love some specific advice. Is Duane's 14lb suggestion too light? Is there a better target weight, or do people generally consider this not something worth doing?

Cheers,
James
It all depends on how the car will be used and how you drive. If you are a hyper driver that constantly bounces off the rev limiter then light is good but if you are a smooth momentum driver then a light flywheel doesn't matter as much so you might as well enjoy the other benefits of a heavier flywheel.

To me all of these decisions center around your ability to be honest with yourself. I have seen many times with both motorcycles and cars that the owner envision themselves doing something that there is zero chance the machine will be used for. The initial excitement of driving the hard core performance machine soon transitions into disappointment. An extreme example is proven by the mileage driven by Bugattis and other hyper supercars. Same situation with bikes like the Ducati 916. There is no joy operating those things on the street. On the street less is more.

As for a flywheel, S90 weight would be as light as I would go for a street car. I think the C and SC had the same heavier flywheel so that should tell you what Porsche felt was correct.
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Al Zim
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Re: Engine rebuild - your advice please

#47 Post by Al Zim »

FLYWHEELS; Light flywheels work well for our customers (we have all types of customers) I cannot deduce a pattern of flywheel weight and customer characteristics! We have no complaints or questions regarding engine performance.
PORSCHE: believed that changing the opening configuration (NOT the activators that attach to the throttle plate but the device that regulates the opening characteristics) BUT the on the 1958 and later carburetors did not need the same configuration (regarding throttle opening curve). as the earlier cars So that is what you got. I cannot imagine how small the savings the factory incurred.
In my opinion I think every decision that Porsche made was a monetarily based. A prime example is the Number 1 main bearing switch from 55MM to 50MM in March of 1963. Engine numbers starting with P*0***800 *** ***. Al Zim
I (WE) through the TALK cannot tell you how to build a 356/912 engine! Or tell you about accumulating correct parts and tools to repair these cars. I have been suspended (numerous) times for this activity. AL ZIM**
In the last 2 weeks we have had 3 (now 4) cars in for major engine restoration. One more that has been malingering here for longer that it should have been. al.
Last edited by Al Zim on Sat Apr 20, 2024 3:00 pm, edited 2 times in total.
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Jacques Lefriant
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Re: Engine rebuild - your advice please

#48 Post by Jacques Lefriant »

Hi Brother Al
We highly appreciate your contributions to the community. You could help us and James by say narrowing down the camshaft selection from the 2000 choices by suggesting a few with their specs and the feedback you have received. Then in the Vendor announcements advertise the ZIM'Z Magic Cam. You could also make an instruction tour video and save us the airfare and lodging to visit you. I am still waiting to see your 7 lb Flywheel i would have trouble driving a car with it but then i am not a racer.
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Al Zim
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Re: Engine rebuild - your advice please

#49 Post by Al Zim »

I cannot tell you what camshaft to use! We correspond with Dema Elgin after we have determined what components are involved and what our results should be. You are limited because of the limitless combination of what has been created Just because something is advertised (possibly by a known shop) does not mean that it will be suitable for your desires. READ all you can. Read Willhoit take notes and read him again! Check your budget! You will need a large one car space in and air conditioned garage. Tables a real work bench and an expensive vice. AND ALOT OF PATEIENCE. al
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Martin Benade
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Re: Engine rebuild - your advice please

#50 Post by Martin Benade »

Don’t you usually use the same compression ratio and fuel injection on most everything? You have no cam that’s your go-to for most engines that you build?
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James Fitzsimons
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Re: Engine rebuild - your advice please

#51 Post by James Fitzsimons »

So, I had my rods magnafluxed and case hot tanked and I picked them up today. The good news is the rods aren't cracked, so I plan on refurbishing those and using them in the rebuild.

The not so great news is I found a small crack in the case. It's taken a smack just to the right of the flywheel at some point, hard enough to put a crack in the back of that web. It's not in a structural location, but I'm wanting your advice on whether it should be welded to prevent it spreading.
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Keen to hear what others would do in my situation.
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Vic Skirmants
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Re: Engine rebuild - your advice please

#52 Post by Vic Skirmants »

That crack is not going anywhere; leave it alone.

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Harlan Halsey
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Re: Engine rebuild - your advice please

#53 Post by Harlan Halsey »

Vic Skirmants wrote: Sat Apr 20, 2024 7:32 am That crack is not going anywhere; leave it alone.
Then grind it out? And recheck?

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Re: Engine rebuild - your advice please

#54 Post by Al Zim »

MARTIN: There are parameters that most of our engines fall into. Unfortunately some of our customers who know how to read become overwhelmed with advice due to lack of engine building experience want to stretch these parameters past reasonable. FOR INSTANCE: every engine is measured at 80 degrees F in the cleanest room in the shop (I mean CLEAN)!
Most of the time they are out for line bore on the main bearings, camshaft bearings. To keep the compression ratio at its peak the cylinder base height is surfaced to keep all the cylinders equal in volume. Now you have spent @ 900 to 1,500 dollars to get the case as it was designed (use only the cases manufactured after March 1963 (see the parts book for serial numbers previously posted) How long will that 60 year old crank last? What happens if you have a S-90 (#1 main bearing @55MM? crank) That is a 60++ year old crank (time for a decision) Can you purchase bearings ? What about the connecting rods the newest one that has been in service is 55 years old. When you pick your camshaft the Porsche connecting rods may not clear the cam lobes! How do you know that? Can you refurbish your 60 year old heads, that have been refurbished numerous times. What are you going to do for a distributor that was first used in 1956? Who is rebuilding generators?
Fuel injection is built to suit! Camshaft design, compression ratio, engine balancing, what about the blower fan on the generator? EVERYTHING HAS TO BE DECIDED. $$$$$ EVERY ERROR THAT YOU PREVIOUS BUILDER OVERLOOKED IS GOING TO COST YOU MONEY! al
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Re: Engine rebuild - your advice please

#55 Post by Al Zim »

Vic: How do you know the crack is going "No Where"?
Harlan: Grind it out an check...THEN what if the case seeps oil. You are not going to grind and then weld the case with the engine assembled?
James: In your experience how do you know the crack is not structural.
FOR SOME REASON THE 356 HAS BECOME INVINCABLE! ?? It is not.
Look for an older (guy) who owns a shop that has modern Equipment. Ask him to show you where he does his case measurements.
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Re: Engine rebuild - your advice please

#56 Post by Al Zim »

MARTIN: I CANNOT TELL YOU WHAT ZIMZ USES. THAT IS ADVERTISING AND WE WILL BE SUSPENDED FROM THE LIST! al
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Re: Engine rebuild - your advice please

#57 Post by Jacques Lefriant »

Hi Brother Al
There are very few readers that will have the opportunity to benefit from your excellent program. I am sure you have seen the worst attempts to rebuild engines but somehow others have managed to rebuild engines that address the use intended reliably. Most of the audience for these posts are attempting to achieve the most practical overhaul by getting advice. Telling them they can't do it or find someone to help is not helpful.
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Martin Benade
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Re: Engine rebuild - your advice please

#58 Post by Martin Benade »

Al, you are a smart guy and a friend. I wish you could understand what advertising was. Naming a particular camshaft that you have had a good experience with is absolutely NOT advertising. It would be helpful information to share.
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Re: Engine rebuild - your advice please

#59 Post by Al Zim »

MARTIN: IT IS ADVERTISING BECAUSE WE USE AND SELL THAT PART! If I say to you we use a 113.650.XXX.05 I am telling you what I am using which means that is what I sell! ...Thus advertising. al
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Re: Engine rebuild - your advice please

#60 Post by Martin Benade »

I think you are misunderstanding this policy. Please ask Mark and report back.
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