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Sat Mar 27, 2010 3:00 pm

I going from the round boss heads to square boss heads on my 1200 / 40hp engine.

The first thing I notice is the old rocker assemblies from the round boss heads don't fit the square boss heads. The rocker studs have a shoulder which won't allow the rockers to go on all the way. Do I need new rocker assemblies? Which ones do I need? Will rockers from a 1600 work?

The second thing I notice is the top cylinder head studs are too short. Will ones from a 1600 work?

Is there any other issues I'm going to run into with this head swap?

:?

Thanks.

Sat Mar 27, 2010 4:15 pm

yes.. use 1600 rockers.

theyre 1.1:1 instead of 1:1 so youll get a tiny bit more lift. and they bolt on no prob.

Sat Mar 27, 2010 4:16 pm

oh and yeh. i think the 1600 ones will work. not sure though, but you do need shorter ones for the top middle two studs for sure

Sat Mar 27, 2010 4:31 pm

glutamodo is the man when it comes to this, I'm sure he will chime in. I just went through this. I opted to keep my round boss because I didn't want to change out my head studs. I don't think 1600 will work but I'm not sure. You are gonna need 34 mm intake manifold gaskets as well. Sorry I can't be more help.
Here is the thread on gaskets, maybe it will help.. http://www.thesamba.com/vw/forum/viewtopic.php?p=4466642&highlight=#4466642

Sat Mar 27, 2010 5:19 pm

This whole head swap is becoming a big pain in the ass. I think I'll just look for some rebuilt round boss heads and sell the square boss heads. shano63, I believe I bought them off the same person (Gary) you bought your 40hp heads from.

Sat Mar 27, 2010 5:38 pm

It is pretty hard to find the correct size upper studs. SP uppers are usuable though, but can be slightly too long, I had to double up on washers on some of them on the engine I'm running now. Although I did later score a set of proper length studs for next time I'm building one of these.

The rockers, you can get shafts from a 1300-1600 and put your rockers on them, or just use the later 1.1:1 rockers if you want - won't make much difference to the engine with those small valves and intake ports.

About giving up, I understand if you don't want to deal with it. I will say that the square boss heads are better though, more fins, (and thus the need for longer upper studs) and no rocker issues. "F" replacement round boss heads came with factory short-studs and are good too. But the squares are the best of the 1200 heads.

-Andy

Sat Mar 27, 2010 5:57 pm

Yeah, I got them from Gary as well. I'm just waiting on gaskets and I can start putting it back together. Good luck, Chris

Sun Mar 28, 2010 5:19 am

My biggest concern is removing one of the cylinder head studs and something bad happening like stripping the threads or worse, cracking the case.

I've got a set of 1600 rockers so that's not a problem.

Mmmm...what to do... :-k

Sun Mar 28, 2010 7:37 am

That's exactly why I didn't do it.

Sun Mar 28, 2010 9:02 am

Ah, I see. 40HP cases can be kind of flaky on their case threads, which is why I recommend case-savers on them. But it's mostly the lowers that give trouble, as those have the constant extra pressure and vibration of the valvetrain spread across them when the engine is running. But I understand your concern.

Sun Mar 28, 2010 10:17 am

Looks like the head studs have already been replaced as they are all 10mm studs and not 8mm.

Good news though - I have the correct intake manifold gaskets!

Sun Mar 28, 2010 10:19 am

Actually, 10mm was the standard thread on VW engine head-studs up until the early 1970s. When VW went to stock case-savers, that's when 8mm head studs came out.

Sun Mar 28, 2010 10:42 am

So, could I remove the studs, install case savers and use 8mm studs just for the top row of studs or should I do them all?

1600 DP studs wont work, I have to get SP studs. Exactly how long are the (top) studs I'm looking for?

By the way, thanks for all the info. :D

Sun Mar 28, 2010 11:23 am

That's the thing, it's the lowers that tend to fail, and the lowers that most benefit from case savers. I remember one time I rebuilt my big-bore 40HP and beore I took it apart, intentionally torqued the heads down to see if they were still solid. They were. Then I rebuilt the engine. And after it was done and I was driving it that winter, one by one, the lowers started to pull out ( I have stale air, so when they'd pull, I 'd know becuase oil would leak, weep down the stud, drip on the exhaust pipe, puff into smoke wihch would blow into the car if the heater was on, and it was winter) So I replaced them all with "fixit" studs, these are slightly oversize self-tapping studs you can screw in those holes where the threads are pulled out. Not nearly as good as case savers but at the time I wasn't wanting to tear it apart again.

But I digress. The uppers are much less likely to fail, never seen one fail actually. And case savers, or helicoils, well, those are machine-in, which means best to do it with the engine apart at rebuild time.

The correct length studs for 40HP square-boss heads is M10 x 193mm. I've talked about this before, they are not easy to come by. I ordered a set once from a Formula Vee shop and they sent me I think 1 correct one and the rest the longer 1300-1600 style. You might be tempted to try to use a tap to extend the threads on those, but I'd rather just double-washer, as cutting threads on those can weaken the stud. (If you compare a 1300 to a 1200-squareboss head they are about identical in external dimensions, so the main difference for the studs is they are shorter on the 1200 becuase of the shorter stroke of the engine)

Another thing I thought I'd mention that I came up with when I was just looking up that stud length, 40HP had two lengths of pushrods, only 2mm apart, but the square-boss heads need to have the longer ones.

Sun Mar 28, 2010 12:04 pm

I just realized case savers are 14mm OD so I'd have to machine the case - screw that as I JUST finished putting the case together yesterday.

I'll look for some good round boss heads and sell my square boss heads.

Sun Mar 28, 2010 12:08 pm

I understand. I'd look for ones with a casting number that ends in F or D.

One factory modifcation to round boss heads that I've always done, is this:

Sun Mar 28, 2010 12:11 pm

anyone have pictures of the square and round heads to compare and what the differences are on the heads . :?:

Sun Mar 28, 2010 12:13 pm

Wait a minute, my push rods look like that:

They measure 270mm.

...and my engine # is 9160667 (Nov 1964) so shouldn't it of come with square boss heads?

:?

Sun Mar 28, 2010 12:17 pm

hsosa1 wrote: anyone have pictures of the square and round heads to compare and what the differences are on the heads . :?:

Round boss:

Square boss:

The boss where the rockers attach.

Sun Mar 28, 2010 12:37 pm

Joey wrote:

Good news though - I have the correct intake manifold gaskets!

Sure, rub it in.. :D