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My Big Bore '40hp' build
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jasengine
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PostPosted: Thu Oct 10, 2013 7:45 am    Post subject: My Big Bore '40hp' build Reply with quote

Thought I would share some of what I am doing: The basic engine is a late 1192cc Type 1 for a Beetle, dual relief case, 90mm holes in the case for the cylinders, 64mm crank.

My build is:
85.5mm Piston/cylinders
1600 twin port heads (35.5mm x 32mm valves)
Scat C25 cam, lifters HD springs
Lightened flywheel
Case tapped for full flow filter and additional oil cooler
64mm Crank assembly dynamically balanced
Standard '40hp' rods with ARP bolts

As the barrels are longer than the 40hp items I have turned them down to the same length.

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Last edited by jasengine on Fri Nov 08, 2013 9:34 am; edited 2 times in total
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beetleseb
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PostPosted: Thu Oct 10, 2013 8:00 am    Post subject: Reply with quote

Looks good. Do you do all your own machining?

What are your plans for the carbs? I have some spare single port dual darb manifolds somewhere.

Seb
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jasengine
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PostPosted: Thu Oct 10, 2013 11:32 am    Post subject: Reply with quote

beetleseb wrote:
Looks good. Do you do all your own machining?

What are your plans for the carbs? I have some spare single port dual darb manifolds somewhere.

Seb


I'm gona use the standard 30 pict 3 to begin with, go up a jet size or so. Depending on how it runs I might leave it at that, or go for some twin singles.

Yep, turned the cylinders myself, but my lathe isn't big enough to do the flywheel lightening.
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hendovw
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PostPosted: Thu Oct 10, 2013 12:12 pm    Post subject: Reply with quote

What are you doing rod/wrist pin combination? the 85.5's are 22mm pin, the 40hp rods are 20mm. 1600 rods are to narrow for your 77mm crank.
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jasengine
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PostPosted: Thu Oct 10, 2013 2:03 pm    Post subject: Reply with quote

hendovw wrote:
What are you doing rod/wrist pin combination? the 85.5's are 22mm pin, the 40hp rods are 20mm. 1600 rods are to narrow for your 77mm crank.


Ah yes, good point. I removed the old bearings from the short rods and bored out the small end to take the larger 22mm bearing. Not as much metal around the upper edge, but a lot of the force is on the downward stroke and as the maximum angle to the piston is relatively shallow compared to a longer stroke, it should be ok. I have read of others doing this with no reliability problems.
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PEPPE
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PostPosted: Sun Oct 13, 2013 10:20 am    Post subject: Reply with quote

i've done many of them. also with 90.5 cylinders (friends have done also with 92mm). i have also special fixtures for lathe to safely modify the barrels. they have to be shortened about 10mm.

you can use also standard 69mm crank. you have to narrow the big end of the rod and slightly trim the underside of the piston (or better use forged ones) to have to clean less.

with those cylinders i would have cleaned also the top of the barrel, because they have less sealing surface then standard ones.
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beetleseb
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PostPosted: Sun Oct 13, 2013 10:47 am    Post subject: Reply with quote

Could you use the same trick on 36hp rods? Would make life easier!

Almost seems a shame to use a 69mm crank.

Seb
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PEPPE
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PostPosted: Sun Oct 13, 2013 10:56 am    Post subject: Reply with quote

i never tried on 36hp. it depends from the "meat" around the bushing.
but another problem is the distance between the studs. i have a friend that used to modify vw barrels for using on dual cylinders aircooled fiat 500s. he does a similar modification to the barrels. i may try to ask some help for the relocation of the stud holes.

85.5 pistons will work on a 36hp? will them fit? will 87.5mm-88mm od barrel fit in the case?

about the 69mm crank i believe that is worse using 1300-1600 singleport heads. at least using a 69mm crank the engine does not change appearance. i always use 1200 heads.
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beetleseb
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PostPosted: Sun Oct 13, 2013 11:03 am    Post subject: Reply with quote

I know 83mm works. And that the 40hp big bore can be modded so wondered about the 1500 b and p's. There is not much meat on a 36hp conrod.

Seb
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jasengine
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PostPosted: Sun Oct 13, 2013 11:15 am    Post subject: Reply with quote

That's quite a large cylinder to put on. What's the performance like with those?

You're right about the sealing face between the head and cylinder, I was going to rub them over some emery paper on a surface plate.
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PEPPE
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PostPosted: Sun Oct 13, 2013 11:19 am    Post subject: Reply with quote

you need precision there. put on the lathe and square them well with the base. otherwise you will have sealing problems.
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jasengine
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PostPosted: Sun Oct 13, 2013 11:38 am    Post subject: Reply with quote

Yep, you're right, thinking about it: the heads might not bolt down on the cylinder tops. A quick skim should sort it
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PostPosted: Sat Nov 02, 2013 2:01 am    Post subject: Update Reply with quote

I have now assembled the case, which took ages as I was making sure I had done everything correctly and it all fitted perfectly. I am now trial fitting the pistons and cylinders, which I have now discovered the piston skirts hit the case! No problem, so I am now machining the skirts to the same height as the original 77mm pistons on the mill. I have probably done this in the wrong order, but it's a learning experience.

I was looking at some of the photos I took when stripping down the engine and noticed the oil slinger is dished away from the case....ahhhhh, I've put it in the wrong way round! I couldn't believe it, I thought I was doing so well. I've now got to strip the case down again and put it in the right way, scraping off all the hylomar and upsetting the distributor drive, which I found a right pain to line up. Oh well, all good experience!

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jasengine
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PostPosted: Sat Nov 02, 2013 4:11 pm    Post subject: Reply with quote

Clearancing the pistons next

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jasengine
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PostPosted: Sun Nov 03, 2013 3:17 pm    Post subject: Reply with quote

All pistons weigh within 0.1g of each other. So on with the build!

Something I did notice when puting the power pully on, that it wouldn't push on easily and the crank was then stiff to turn. I measured the hub and compared to the original vw pully it was 0.1mm larger in diameter, just enough to pick up on the case! So I had to turn that down a little, which didn't clean up fully with a small skim, so that was a crappy bit of machining by Scat!
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PostPosted: Sun Nov 03, 2013 3:43 pm    Post subject: Reply with quote

Why the choice of a power pulley over a stock sized pulley?
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jasengine
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PostPosted: Sun Nov 03, 2013 4:01 pm    Post subject: Reply with quote

Many moons ago, i thought it would be a good idea to get a few extra hp and stop the fan from exploding at high revs.

As this will reduce cooling, I will be running an external oil cooler with thermostatically controlled fan.
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jasengine
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PostPosted: Fri Nov 08, 2013 9:31 am    Post subject: Reply with quote

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Measuring deck height at the moment and I need to make a 4 bolt plate so I can torque it down evenly to get an accurate deck measurement. I'm getting @ 0.24mm on one cylinder and 0.54mm on another, but I understand it should be at least 1mm.
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PostPosted: Sat Nov 09, 2013 6:57 am    Post subject: Reply with quote

what is the benifit of building a 1600 on a 40hp case?

seems you are not trying to make this "look" like a 40 b/c you are using dual port heads; is the 40hp case not much weaker than a 1300-1600?
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PostPosted: Sat Nov 09, 2013 12:04 pm    Post subject: Reply with quote

StockNazi wrote:
what is the benifit of building a 1600 on a 40hp case?

seems you are not trying to make this "look" like a 40 b/c you are using dual port heads; is the 40hp case not much weaker than a 1300-1600?


Same case on "newer" 1200 and 1600 Smile

So the 1200 is probably "better" than a 1600, because of lower output.
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