Arild
Active Member
And now there is snowing! Already 10cm of wet snow. Me dont like - I like Thailand!!
VW Beetle engine 1/5 scale
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And now there is snowing! Already 10cm of wet snow. Me dont like - I like Thailand!!
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Your VW build is fantastic! I used to have a 1969 Karman Ghia. Rebuilt the engine from 1500 to 2000cc displacement. Not a good car for a starving college student with little money, especially cold Canadian winters HaHa. But I do have a few fond memories.
I'm interested in your initial design work flow. Did you use factory engine drawings for background layer reference & developed the CAD model off that?
I posted a few carburetor charts on the forum, here are some links. I suspect there are many variables involved, but one of the stronger initial estimate correlations seems to be displacement to throat size assuming typical RPM & cam timing. Please note some of this information pertains to methanol fuel vs. gasoline (methanol = larger orifice) so I tried to label that distinction. I also wondered about how much to increase carb size based on multiple cylinders when I built my radial. The usual suggestion is add proportionate to combined intake period of multiple cylinders. But maybe an overview comment from my own reading - seems like many builders initially estimate a bit large based on scale factor & end up with something a bit smaller in real life running. So all I would say is - integrate a design plan where you can swap different size carbs with little effort, or ability to modify the intake throat diameter. Look forward to more build pictures when you post!
https://www.homemodelenginemachinis...-917-flat-12-engine.32972/page-16#post-374923
https://www.homemodelenginemachinist.com/search/2133740/?q=carb+sizing&c[users]=petertha&o=relevance
https://www.homemodelenginemachinist.com/threads/2-stroke-twin-wont-start.26098/#post-285862
Arild
Active Member
I found an drawing at the open source "onshape" community. But I had to modify it, as it was not good enough for an model engine. I've already started to a make a 904 to fit that engine. If I don't succseed with my engine, I will make that car electric! What a negative tought!! Karman Ghia was also on my list!
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I am enjoying your postings. Pleased you mentioned the Karmann as a possibility. I like the Karmann styling as much as a 356. I used to have a '69 Ghia in appropriate "Texas Yellow"
Jan Dressler
Member
Very nice Beetle engine, I am watching and learning...
Regarding the 904, the original one had the Fuhrmann quad overhead cam engine. No pushrods in there... Shafts and bevel gears, lots of them. A nightmare to set valve timing.
as long as the valve clears the piston*, and the valve spring coils don't bind, the higher lift should be ok. check for valve to piston clearance.
we often refer to this engine as the 4-Cammer. Here's pics of some of the work I've done in the past couple of yrs on the full size Type 547 engine for a 550 Spyder. I've been involve with casting & machining replacement cylinders for them too ( four pics are raw castings; we chose to make individual heads (like 911) and then a cam support casting. I rebuilt & rebalanced the cooling fan, last to pics of of a used engine my customer was trying to buy.) It takes me about 9 hours to assemble the heads, cams and drive shafts, fit spacers to set gear lash & endplay, etc.
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Tom-
You need to start a separate thread for your VW engine work.
Those are some fantastic mods to a VW engine, and this work deserves its own thread.
What a nice and clever piece of work !
.
You need to start a separate thread for your VW engine work.
Those are some fantastic mods to a VW engine, and this work deserves its own thread.
What a nice and clever piece of work !
.
Arild
Active Member
Aligning up the engine body and mill out the slot for camshaft bearing.. Then make a closed end brass bearing at the flywheel end.
The other end bearing will be more difficult, as it is off-center due to the oilpump (I'll not have a oilpump, and see how it goes with just "splash lubrication).
I used brass as bearing on this one as a mistake, all the other (and gears) are in bronze. But I read about it and brass on steel are pretty good bearing too!
However, progress is a bit slow for the moment. It's soon Christmas and my wife complain that I don't do enough housework and preparations!
The other end bearing will be more difficult, as it is off-center due to the oilpump (I'll not have a oilpump, and see how it goes with just "splash lubrication).
I used brass as bearing on this one as a mistake, all the other (and gears) are in bronze. But I read about it and brass on steel are pretty good bearing too!
However, progress is a bit slow for the moment. It's soon Christmas and my wife complain that I don't do enough housework and preparations!
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Arild
Active Member
I made up a drawing to better understand the opening and closing. When I transfer this to the cam, I divide the degree by 2. The relation between intake and exhaust is the, 17.25deg (+180/2) at top of the lobes. (107degree). Both intakes lobes are 90(180)degree apart, and the same for exhaust lobes. Am I correct? I 3D printed the cam and compared with pictures of the original. It seems correct for me.. Last picture is a jig to be used when milling. I'll mill down roughly and then use a hand file to make it smooth.
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looks good
Looking good!Aligning up the engine body and mill out the slot for camshaft bearing.. Then make a closed end brass bearing at the flywheel end.
The other end bearing will be more difficult, as it is off-center due to the oilpump (I'll not have a oilpump, and see how it goes with just "splash lubrication).
I used brass as bearing on this one as a mistake, all the other (and gears) are in bronze. But I read about it and brass on steel are pretty good bearing too!
However, progress is a bit slow for the moment. It's soon Christmas and my wife complain that I don't do enough housework and preparations!
A bit of trivia:
Many VW mechanics may be unaware of the method VW used to compensate for cam/crank gear backlash (due to variances between crank and cam bore center-line axis.) VW made cam gears with +/- circular tooth widths. Cam gears were made & marked from +8 to -8 . Each step is 0.01mm. A "standard" cam gear was either stamped "0" or had no marking.
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Arild
Active Member
It took me a while to get the correct 2mm slot to that wheel. I got a tool to stramp out that slice, but after some trials, I figure out it always make a bigger a slise that I want;
So, instead I filed a slot. No it got a perfect fit! .. And yes, this will never bee a 100% VW engine, but close too! At last fjucked it up by drilling through the wall of the (oppsite) crankbody, now that was fixes by a pressfit and glu. Next up will be top make the 2x2mm "lock slot" for the crank!
(the very small spacer is for my damage in my brain that I miscalculated 0.5mm in the bearing - just a spacer)
The cam and crank now run smootly!
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