TheSamba.com :: View topic - My first build! 40hp big bore need advice

Sat Apr 04, 2015 3:57 pm

tore down the og. engine that came out of my (early) '63 Bug last night. I have most of the parts I will need for this build but still lack a few major components (i.e. heads, specifically). Here's what I have: The original crankcase #6981504. Currently has std. crank bearings which hints to me that the po wasn't lying when he told me he said that he didn't think the engine had ever been rebuilt. My plans for the case at this point are to send it out for align bore, machine for cam bearing inserts, and add case savers. I have a stock cam and stock reground crank (is counterweighting recommended?) with stock reman rods. For the p&c's I have a nos set of old school made in japan JH 83mm (big bore). The heads? I'm not sure yet. I have the heads that came off this engine but I'm not so sure that they will be my best choice for this build. They are early type 3 heads...single port with flat manifold mounting so they work on type 1 (although I now know why I busted welds on two different intake manifolds BC I had to stretch them to get them to fit.) The cylinder sealing surface on these type 3 heads is not cut as deep as the type 1 head, therefore the engine was actually wider by about a quarter inch compared to what it should be. Shouldn't they have been flycut? Seems like compression would have been way low.
Anyway...I'm going to need help from you seasoned builders along the way. Any advice is welcome and appreciated.
Here are some preliminary questions before I get too far with this. Keep in mind that this needs to be built on a tight budget! Suggestions for heads? Are the type 3 heads a good choice for this? The intake (I think) valves are bigger than type 1 40hp heads. Otherwise, if I go with type 1 40hp heads, would you suggest the late square boss style or would the earlier round boss heads suffice with short stud kits installed? From what have read, the square boss heads would require the added expense of longer head studs, longer pushrods, and different rockers. Am I correct here? Another question...anyone have experience with the JH 83mm p&c's? Clearance issues? And just something to point out...I want this to be fairly close to stock other than the big bore kit...nothing wild. I did however convert it to 12volt before I tore it down so it will have an alternator in the engine bay rather than the 6 volt generator it came with. So, stock-ish, but practical!
Again, advise is welcomed! I will post pics of progress as it happens if this topic sparks some interest. I hope so!

Sun Apr 05, 2015 8:23 pm

I built an early 63 40hp with a stock 69mm crank from a 1600 and used the mahle 83mm big bore kit. Had the case line bored and cam bearing bore done. Rimco said don't bother with case savers unless there's a pulled stud. Had to put in .100 cylinder shims for the longer stroke. I had to do some very minor case clearancing for the piston skirts. I used round boss heads and had them reworked for 8:1 cr and put in the short stud kit. Had the original cam and lifters reground with some extra lift and used 1.1:1 rockers. I had no problem stretching my intake to fit the slightly wider engine either. You don't need a counterweight crank unless you plan a lot of revving above 5000rpm. A lot of your questions are addressed in the "how to hot rod the VW engine" book. It's a good resource for building a vintage speed engine.

Sun Apr 05, 2015 9:05 pm

bugmandave wrote: I built an early 63 40hp with a stock 69mm crank from a 1600 and used the mahle 83mm big bore kit. Had the case line bored and cam bearing bore done. Rimco said don't bother with case savers unless there's a pulled stud. Had to put in .100 cylinder shims for the longer stroke. I had to do some very minor case clearancing for the piston skirts. I used round boss heads and had them reworked for 8:1 cr and put in the short stud kit. Had the original cam and lifters reground with some extra lift and used 1.1:1 rockers. I had no problem stretching my intake to fit the slightly wider engine either. You don't need a counterweight crank unless you plan a lot of revving above 5000rpm. A lot of your questions are addressed in the "how to hot rod the VW engine" book. It's a good resource for building a vintage speed engine.
If I could get away without the expense of counterweighting the crank (whatever that costs) and the case savers (rimco quoted me $125) it would help. I also already have a reground 64mm crank that I would like to use. And what about those type 3 heads I have? Couldn't I just have them flycut to the same depth as a type 1 head and run them? I would think that the bigger intake valves in them would be a benefit with the addition of the big bore kit. This all just seems to me to be the most cost effective way for me to go about this and cost effective is important...I don't have a whole lot of dough to throw around! Is my cost effective plan also a good one for reliability and longevity purposes? This is also important to me.

Mon Apr 06, 2015 11:59 am

I'm not familiar with the type three heads but yes bigger valves would work. Remember if you fly cut heads you will increase the compression ratio so you may have to cc the combustion chambers to get the cr back down to a tolerable range. Reliability depends on several factors. Precision building and driving practice are two of them.