MK9 Case Cracking

[Will Velkoff]

In 2013 I had a large crack in my MK9 housing (near the bellhousing area where the clutch/flywheel are). The attached photo was from after it was welded back up.

When I was going through the car after the last race I found another crack in the same spot, adjacent to the weld.

Has anyone tried to reinforce the case? By gussets or by bolting support onto the studs in the side plates? It appears the cornering forces are cycling the transition from the main center section of the case to the bellhousing part of the casting. The right side keeps cracking, which makes sense for the clockwise tracks we run.

If not, I'll just blend out the crack, and weld it back up. But I'd like to see if anyone has been able to reinforce this to prevent re-occurrence.

Thanks

[Rick Kirchner]

Perhaps it's not the case, but an issue with the subframe that's allowing the whole mess to flex and the bell is taking that load.

[john f]

Trying to re-weld it is like pi$$ing into the wind! It will return. Re-case it and forget about it. Others may disagree, but just my $0.02.

john f

[S Lathrop]

I have had success with doing a brace that reduces the loads in that area. On one of my FSVs I made a brace and just drilled a small hole at the end of the crack. That setup worked just fine. The crack never got worse and I raced the car for a couple years, with the crack.

Many early FFs mount the engine and transmission with the ears on the transmission and the side mounts on the engine block. The Zink Z10 was this way. If you picture an axis of rotation between the engine mounts and the transmission mounts, Most of the engine mass is forward and above that axis. When you corner, the torque load about that axis is enormous, way more than the transmission case can support. Adding a mount at the top and front of the engine and a mount at the bottom of the bell housing will do wonders to reduce the cracking, and actually stop and prevent cracking..

Trying to fix the case or even replacing it is futile in stopping the cracking. You have to fix the structural problem that causes the cracking.

[Bill Manofsky]

Perhaps it's not the case, but an issue with the subframe that's allowing the whole mess to flex and the bell is taking that load.

I agree with Rick, It is most likely from distortions in the chassis. You can do all the repair welding you want and it will keep cracking.

Did the car ever take a hit to the rear corners that would have bent the frame or motor mounts? Do you have to force fit the tranny or engine mounts to get it in?

One of your motor mounts could be bent too.

It is the age old structural engineering adage about the three legged barstool is better than a four legged one.

With a three legged stool, all three legs will touch the floor no matter how uneven it is.

Try that with a four legged stool on an uneven floor and you always have to make the fourth one adjustable. Same reason why you have to put pack of sugar under the leg of wobbly table at a restaurant.

When the weld up the frame at the factory, they use a jig that represents the four hard points mounting the engine and the tranny. If your frame or motor mounts are bent and no longer top that configuration, then you have to force fit the engine and tranny in place and thus preload them. The weak link in the tranny case since the engine block is fairly inlfexible.

If there was only the two engine mounts and a single mount on the tranny, that would be a total of three mounts and would fit without any preload no matter how bent the frame or motor mounts are.

Bill

[Will Velkoff]

Steve,

Thanks for the suggestions. Do you have any photos of the additional braces you added?

The front engine mount will be a rather simple one to fabricate. Where and how did you tie the adapter plate/bellhousing area into the chassis?

[R. Pare]

You can make a brace that reinforces that particular area by using the two holes already available and bracing across to one (more preferably two) of the side plate studs. It won't "cure" the cause of the stressing, but it will spread it over a larger area that will be much less prone to cracking.

[S Lathrop]

Will,

To add to Richards description, I made braces from the main transmission mount (the side plate extensions) to one of the 2 holes in the bell housing where VW mounted the tranny in the Beatle. I did have to modify the slave cylinder bracket because I used one of those holes on that side.

I also added a tab to the rear bulkhead so that one of the 2 bolts that hold the bottom of the tranny to the bell housing/engine adapter went through that tab.

At the front of the engine I ran a brace from one of the generator bosses on the left side of the block, just below the head over to the roll bar bulkhead. On the Zink Z10, I just used the mounting point for the rear upper trailing link. On later cars I ran an aluminum plate mounted on the water out let on the head. That plate was also mounted to an aluminum block mounted to the front of the head on the right side where there is a large cast pad.

On the Z16, the front engine mounting went from both sides of the block to the roll bar. The Z16 had less of an issue cracking the VW bell housing. I think that this was because the engine was really secured to the chassis. The transmission was more of a structural member in the chassis than the Z10 but the Z16 had way less of an issue cracking the tranny case.

[jgaither]

Just discovered mine is cracked. Previously repaired in a similar area but separate from this one. Crack goes down the side towards the side plate - not sure yet if all the way there, but close anyway.

Wondering if the case should be replaced at this point and perhaps have someone fabricate some arms to spread stress as Steve and Richard suggest.

Where might one source a case for a MK9? Any idea what is a reasonable price to pay?

Thanks,

JG

[Bob L.]

Data points:

Ebay had 2 older cases, said for MK9s (looked right, but aged), that finished up today, one sold for 112.xx and other 81.xx.

I bought an alum. rhino case last fall for a recase job, think it was around $300 + shipping, plus: had to be modified for reverse, as well as other outside clearances... didn't come with studs for side plates, either... bit more weight, but think it's stronger, less chance to crack... Check Rancho products in Calif... buggy stuff...

Have had a couple others welded up up over time...some held, some didn't...

Bob L.

[Bill Manofsky]

All these cracks look like failure from torsional stress.

I am pretty sure that the loading is caused from having four mounting points for the engine/tranny assembly.

If there were just three tie down points...two on the engine and one on the tranny, you may not see these cracks.

I am wondering if this is a problem especially endemic to Lola T540's because of the motor mounts up a the front of the engine instead of on the sides of the engine.

Bill

[S Lathrop]

I think Bill is right about these cracks being caused from twisting.

My analysis, and I have experience to back up my explanation, is the loads that are doing this come from the engine not being fully restrained. The 2 side mounts on the engine and the two mounts on the transmission result in a big torque load about the axis formed by the four mounts. Most of the mass of the engine in above and forward of this axis. And I think is the loads on the engine that is causing the transmission to fail.

When I built the Zink Z16, the engine saw mounted at the front with what can be described as a motor plate. The roll bar on that car went to the bottom of the chassis and the motor plate attached to the roll bar 2 bolts on each side that were 8" apart vertically. We built a special bell housing for that car that we had 2 mounts on either side that attached to the bell housing. On that car the transmission case carried a lot of the suspension loads., much more that the Zink Z10 did. The Z16 had very few problems cracking the transmission case and a very simple brace would stop the crack from propagating.

So my recommendation would be to add an engine mount to cylinder head on the boss that is on the side of the water outlet. On my current cars, I have a 1/4 aluminum plate that goes from the water outlet to the roll bar on both sides. That plate mounts with the 2 bolts on the water outlet and also has a block that extends down from the plate to mount to the boss on the front of the head.

We solved the problem on the Z10 when we added a brace from the top of the block to the roll bar bulkhead. We also ran the bolt on the bell housing, where the VW starter would go, through a boss on the rear bulkhead. We solved the cracking problem by restraining the engine way better than the 2 side mounts and the bell housing will do.

Changing to the rhino case is a really good idea, as well.

[DaveW]

Back when I had a FF with a MK9 (early '80's), it looked to me like the cracks were due to lateral bending combined with the severe stress riser going from the bell housing to the much narrower transmission section. I made a steel-tubing "X" brace (closed across the top and bottom) that went from the OE mounting ears to the rear cross-member, IIRC, that helped transfer those loads across the stressed area and kept the cracks (after drilling their ends) from spreading. Unfortunately, it's been too long and I don't have any drawings or pictures of it. Welding by itself did not work - it just cracked again.

[Bill Manofsky]

I think Bill is right about these cracks being caused from twisting.

My analysis, and I have experience to back up my explanation, is the loads that are doing this come from the engine not being fully restrained. The 2 side mounts on the engine and the two mounts on the transmission result in a big torque load about the axis formed by the four mounts. Most of the mass of the engine in above and forward of this axis. And I think is the loads on the engine that is causing the transmission to fail.

When I built the Zink Z16, the engine saw mounted at the front with what can be described as a motor plate. The roll bar on that car went to the bottom of the chassis and the motor plate attached to the roll bar 2 bolts on each side that were 8" apart vertically. We built a special bell housing for that car that we had 2 mounts on either side that attached to the bell housing. On that car the transmission case carried a lot of the suspension loads., much more that the Zink Z10 did. The Z16 had very few problems cracking the transmission case and a very simple brace would stop the crack from propagating.

So my recommendation would be to add an engine mount to cylinder head on the boss that is on the side of the water outlet. On my current cars, I have a 1/4 aluminum plate that goes from the water outlet to the roll bar on both sides. That plate mounts with the 2 bolts on the water outlet and also has a block that extends down from the plate to mount to the boss on the front of the head.

We solved the problem on the Z10 when we added a brace from the top of the block to the roll bar bulkhead. We also ran the bolt on the bell housing, where the VW starter would go, through a boss on the rear bulkhead. We solved the cracking problem by restraining the engine way better than the 2 side mounts and the bell housing will do.

Changing to the rhino case is a really good idea, as well.

Yes.....in fact on the Lola T342, the frame cross member that has the two tranny mounts is removable where the same member is an integral part of the welded frame.

This means that Lola used a jig to locate the two tranny mounts in space to align them to the two engine mounts when they welded the whole rear end of the frame together. Thus if your engine/tranny assembly does not confirm to that jig, then that fourth bolt is a force fit thus imposing a torsional pre-load on the assembly.

The removable cross member on the T342 allows for some slop in installation. Also the bolts holding it down are in shear so the hole tolerances allow for some movement, adding to the legend of the "flexi flyer".

The weak link is the thin walled tranny housing. The failure is from fatigue loading from the repetitive twists the chassis undergoes during a race.

I wish yo could share some photos of what you describe.

Bill

[S Lathrop]

I wish yo could share some photos of what you describe.

Bill

Here is a Z16 I converted t to outboard some time ago. Note the front engine mount. There is a similar structure on the other side.

[Bill Manofsky]

Here is a Z16 I converted t to outboard some time ago. Note the front engine mount. There is a similar structure on the other side.

That is quite good.

I would think the best design would be to use the two tranny mounts as shown. The motor mounts would include
struts much like the suspension trailing arms with adjustable Heim joints at each end. The would come down from the engine at 45 degree angles to take both Y and Z loads. (Y being left to right and Z being up and down). X loading would be taken by the tranny mounts. One end would pick up the motor at either the standard mount on the side of the block or a bracket near the front of the engine. The other end would go to a pickup point on the frame using a standard rubber engine mount. There would be a strut like this on both driver's left and right on the engine affording infinite adjustability to take out the torsional load.

The current Lola T540 Driver's right front engine mount design is pretty ludicrous contraption that uses the timing cover as a spacer....for which it was never intended. (see photo below). The mount picks up the 1/4 in dia timing cover mounting bolts. Since the shear load is applied the distance equal to the thickness of the cover away from the block, and the cover mounting holes are very sloppy, the 1/4in bolts are then exposed to some very serious moment loads when there is any torsional load on the frame. The driver's left motor mount is very robust and takes out most of the lateral loading and deflection. Without it, the driver's right mount would fail.

I think I am going to redesign the driver's right motor mount on my T540E to include an adjustable strut.

[Bill Manofsky]

Here is a Z16 I converted t to outboard some time ago. Note the front engine mount. There is a similar structure on the other side.

That is quite good.

I would think the best design would be to use the two tranny mounts as shown. The motor mounts would include
struts much like the suspension trailing arms with adjustable Heim joints at each end. On end would pick up the motor at either the standard mount on the side of the block or a bracket near the front of the engine. The other end would go to a pickup point on the frame using a standard rubber engine mount. There would be a strut like this on both driver's left and right on the engine affording infinite adjustability to take out the torsional load.

The current Lola T540 Driver's right front engine mount design is pretty ludicrous contraption that uses the timing cover as a spacer....for which it was never intended. (see photo. The mount picks up the 1/4 in dia timing cover mounting bolts. Since the shear load is applied the distance equal to the thickness of the cover away from the block, and the cover mounting holes are very sloppy, the 1/4in bolts are then exposed to some very serious moment loads when there is any torsional load on the frame. The driver's left motor mount is very robust and takes out most of the lateral loading and deflection. Without it, the driver's right mount would fail.

I think I am going to redesign the driver's right motor mount on my T540E to include an adjustable strut.

[S Lathrop]

It may not be obvious, but there is a steel bracket on the back side of the flange for the cam gear cover. The aluminum plate bolts on the c front over the aluminum cover. The steel plate is off set so the bolts on the front go through the aluminum plate (right side engine mount), the cover, the block and the steel bracket. That bracket is bent to also bolt to the aluminum plate. I did drill out the threads in the block.

On the left side there is an aluminum block that bolts to the 2 bosses on the left side, front of the block. There is an aluminum plate for the left side that bolts to that block and to the roll bar just like the right side.

We did not have aluminum pans for the FF engine at that time (1978). Had to wait for Swift to come along with that refinement.

[Bill Manofsky]

It may not be obvious, but there is a steel bracket on the back side of the flange for the cam gear cover. The aluminum plate bolts on the c front over the aluminum cover. The steel plate is off set so the bolts on the front go through the aluminum plate (right side engine mount), the cover, the block and the steel bracket. That bracket is bent to also bolt to the aluminum plate. I did drill out the threads in the block.

On the left side there is an aluminum block that bolts to the 2 bosses on the left side, front of the block. There is an aluminum plate for the left side that bolts to that block and to the roll bar just like the right side.

We did not have aluminum pans for the FF engine at that time (1978). Had to wait for Swift to come along with that refinement.

Yeah, I saw that bracket.

[Phil Haggerty]

The housing is a VW IRS, and used to be quite easy to find. I bought three at $50 each for complete transmission. They all look the same on the outside, right down to the numbers, but had some differences in the layout inside. Two of three were right, and with a die grinder I had it prepped for the Hewland internals in less than 1/2 hour

[DK540]

From Steve: "So my recommendation would be to add an engine mount to cylinder head on the boss that is on the side of the water outlet. On my current cars, I have a 1/4 aluminum plate that goes from the water outlet to the roll bar on both sides. That plate mounts with the 2 bolts on the water outlet and also has a block that extends down from the plate to mount to the boss on the front of the head."

Having a Z-16, and being much appreciative of Steve's advice and patience - I added the Swift oil pan to mine and tied that in to the frame at the bottom of the roll bar. Happy to show that work to anyone at a VRG/VDCA vintage race. Should I consider adding the plate between the water outlet and roll bar at the top? Do you have a photo of that? Is there anything else I can/should do to prevent over-stress of the gearbox case?

Thanks! Enjoying the Z-16 while I'm learning to drive and race (2 years into this).

David K