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Autocraft 910 cylinder head issue
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steve34
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PostPosted: Wed Dec 13, 2006 11:54 pm    Post subject: Autocraft 910 cylinder head issue Reply with quote

I built a 90mm by 101.6 race motor with Autocraft heads and wasser boxer case. I finaly got around to setting the rocker geometry and shimming the 1.46 ratio rockers for lineup on the lash caps. it seems with the 52mm intake and 40mm exhaust etc. the pushrods rub the sides of the cylinder head pushrod holes. The 3 and 4 cylinder head rubs to the aft of each hole and the 1 and 2 cylinder head towards the front. I wonder if I should die grind the holes to a bigger circle since the Sachette pushrods will allow me to go at least an 1/8 inch bigger in diameter without losing seal area. Or should I send it off and have the holes welded shut, then redrillled and recountersunk? I could machine some exact fit aluminum tubing to fit over the Sachette pushrod tube big end and stretch vanagon seals on yhem. This would give me greater seal potential. I wonder>>>.I could
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nsracing Premium Member
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PostPosted: Thu Dec 14, 2006 6:43 am    Post subject: Re: Autocraft 910 cylinder head issue Reply with quote

steve34 wrote:
I built a 90mm by 101.6 race motor with Autocraft heads and wasser boxer case. I finaly got around to setting the rocker geometry and shimming the 1.46 ratio rockers for lineup on the lash caps. it seems with the 52mm intake and 40mm exhaust etc. the pushrods rub the sides of the cylinder head pushrod holes. The 3 and 4 cylinder head rubs to the aft of each hole and the 1 and 2 cylinder head towards the front. I wonder if I should die grind the holes to a bigger circle since the Sachette pushrods will allow me to go at least an 1/8 inch bigger in diameter without losing seal area. Or should I send it off and have the holes welded shut, then redrillled and recountersunk? I could machine some exact fit aluminum tubing to fit over the Sachette pushrod tube big end and stretch vanagon seals on yhem. This would give me greater seal potential. I wonder>>>.I could


What have you done now? Very Happy

When you get into the hybrids you are on your own. This is rarely charted territory.

The usual is welding and move the holes over to where you need them.
The bottom line is the needed alignment on the rockers and the rest of the valvetrain.

That is one big motor. I am doing the same project with CB Elimantors.
Not that big a stroke though.
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Marty Staggs
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PostPosted: Thu Dec 14, 2006 10:00 am    Post subject: Reply with quote

Are you running tapered pushrods? If not, that may be a simple solution.
How about posting some pics for us?
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steve34
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PostPosted: Thu Dec 14, 2006 10:03 am    Post subject: Re: Autocraft 910 cylinder head issue Reply with quote

nsracing wrote:
steve34 wrote:
I built a 90mm by 101.6 race motor with Autocraft heads and wasser boxer case. I finaly got around to setting the rocker geometry and shimming the 1.46 ratio rockers for lineup on the lash caps. it seems with the 52mm intake and 40mm exhaust etc. the pushrods rub the sides of the cylinder head pushrod holes. The 3 and 4 cylinder head rubs to the aft of each hole and the 1 and 2 cylinder head towards the front. I wonder if I should die grind the holes to a bigger circle since the Sachette pushrods will allow me to go at least an 1/8 inch bigger in diameter without losing seal area. Or should I send it off and have the holes welded shut, then redrillled and recountersunk? I could machine some exact fit aluminum tubing to fit over the Sachette pushrod tube big end and stretch vanagon seals on yhem. This would give me greater seal potential. I wonder>>>.I could


What have you done now? Very Happy

When you get into the hybrids you are on your own. This is rarely charted territory.

The usual is welding and move the holes over to where you need them.
The bottom line is the needed alignment on the rockers and the rest of the valvetrain.

That is one big motor. I am doing the same project with CB Elimantors.
Not that big a stroke though.


Dont go 90mm.Even after clearancing the 3/8ths rod bolt Hbeam rods,I still had to clearance the cam. Had I stayed with 88mm, there may have only been .020 clerancing on the cam. DPR di d the crank. It was a 76 mm core. I opted to go with a wasserboxer crank, 200mm outer and 914 center flywheel. The flywheel and crank are dowelled also.
i plan on never letting the motor go past 6700 to 7000 rpm. I used the original German bearings etc. dry sump with 2 stage pump.

I have only ported the heads , square ported the intakes, redone the chambers, and installed titanium valves. I think I will make the holes larger with a die grinder and recountersink by hand. I have some older aluminum pushrods I can use as shim material. I would be ideal if some cpvc water line would fit over the end of the sachette pushrod tube. I could cut little pieces and use for circular shims. This would allow stretching of the vanagon seal to a point. Actually, I could go to Boeing surplus and get an aluminum countersink and just drill the hole at the angle that the pushrod is at. Jig up the head with a slight anglefavoring one side., then countersink a hole a 1/4 inch bigger and deeper. then dia grind the !/D untill I get appropriate clearance. I could get some aluminum tube and machine to fit the sachette ends. I think I can just die grind an oval that will clearance enough and just black rtv it dry.

a type 1 crank will work with a .060 over rear bearing double thrust. Use stock wasser boxer bearings and a custom fit type 1 thrust bearing. The crush is a little sloppy. I think some guys cut the case to .080. I think I would just teflon the O/D of the thrust bearing and install it that way. Another fellow just peened the O/D all the way around with equal number of peens. It allowed for adequate crush. Since it is a race motor, it wont matter. I have an adapter ring to install a type 1 seal also.

here would be a good combo

century 84mm crank and 5.5 hbeam rod kit $295
101.6mm piston and liner kit $500
bare undrilled comp eliminators cut for 101.6mm and drill for 101.6mm bolt pattern.

I stayed with the 76mm wasser boxer crank because ease of parts selection.

vanagon bearings all stock
no wedgemating
better material in the crank
shift at 7000 rpm so the crank wont break or load the rod bolts

if it cracks, i will just install a cheapy 86mm type 1 crank.

i have never seen a crank crack or break. If I shift at 7000 verus 8500, the crank will not break, and the dial in will be maybe .2 seconds slower. The rod bolts wont break either. The bearings will last a season. I will never have to change the K800 springs. So 10.50 instead of 10.20 I will be running it with a fan shroud, muffler, 48 idas, and a swingaxle, super beetle mainshaft, and 1.65 3rd 1.19 forth with street tires. I will just sandbag 12.01s. A flat 12 as far as I am concerned is a fast car. I will smoke the tires through second. This way the ring and pinion lasts. No slicks for this car. Just a straight bake show 12 second 280 horse bug. peace love and remember JEBSTUART and Yellow Tavern
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nsracing Premium Member
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PostPosted: Thu Dec 14, 2006 10:57 am    Post subject: Reply with quote

I will run the 78mm x 101mm...wasser case.

I called CBPerf and I was informed that the new castings on the CB Elimanotors will be ready by January. I will get mine undrilled also and I will just machine it to fit the Wasser case without mods...less work for me.

Now that I got the Stewart Warner balancer and StormVulcan crank grinder, the sky is the limit pretty much what I could whip up in the garage. Very Happy It has been an uphill climb for me updating the equipment but I hope it will be worth all that.

We shall see though.

Do post on how you fix this problem with the pushrods.
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All other info, lineboring or machine work, dynamic balancing, PM me.
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