Gearbox adapter plate minimum thickness for threaded holes

[TurboRA28]

Hi all, I am thinking about making a gearbox adapter plate for the 1mz so I can straighten up the gearbox.. Not really happy with the 10 - 15 deg slant.

Now I am thinking of making up an adapter plate that will bolt inbetween the bellhousing and gearbox.

Basically the plate will bolt firstly to the gearbox using countersunk head allen key bolts. Then the plate will have holes tapped into it along with dowels for the bellhousing to bolt to.

I want to keep the thickness to an absolute minimum as to not cause problems with clutch and spigot bearings.

So what is the minimum thickness I can go?

The bolts are M10x1.25.

I used to always work off that with a M10 bolt you can get away with a 10mm tapped hole. Is this acceptable?

Different materials can be thinner say mild steel compared to alloy?

Thanks
Joel

[JustenGT8]

Tilt engine?

[AdrianS]

I did an adapter plate in 12mm alloy for a diesel boat I had once. Never gave a problem. I worked out the thickness from an engineering handbook on minimum thread engagement. Steel plate could be a bit thinner - 10mm should be ok (but don't call me if it fails).
General layout was identical to yours - c/sunk high-tensile allen bolts holding the plate to the box, dowels and tapped holes to the bellhousing.

[Billzilla]

As mentioned above, 12mm will be fine - the bolts shouldn't have much load on them at all as to do it properly the bell housing should have locating studs, to take the torque loading. The bolts just clamp the bell housing to the back of the engine and take no torque loads.

Edit - To give an example of this, back many years ago the factory Ford Escort rally cars in the UK used to break gearboxes quite often and to make sure they finished a rally they had to change the box every chance they could. What they ended up with was a bell housing with the locating studs like I mentioned, but to clamp the box to the engine all they used was a big v-clamp, like the ones that hold the lid on 20 litre or so drums of paint or other liquids. Just undo the tailshaft bolts, the clutch, and then the clamp and the box is out in seconds.

[allencr]

...plate for the 1mz so I can straighten up the gearbox.. Not really happy with the 10 - 15 deg slant. ...keep the thickness to an absolute minimum...

Cut the bell-housing & weld. Setup's a PITA without a jig or use a engine block with a piece of pipe held in by the mains to line it up..
I'd like threads at least 1.5 * bolt dia. in aluminum alloy.

[TurboRA28]

Thanks all for info.. As allencr said, it may be easier to cut and weld the bellhousing.

To ensure the input shaft lines up to the crank could I do this..

With the bellhousing attached to the gearbox, get some pipe with the same ID as the OD of the input shaft and slide it over the input shaft. Cut this so it lines up with the face of the bellhousing, then weld a bar to the pipe that could bolt to a few of the bellhousing bolt holes that would normally bolt to the block.

Then that can be the jig for when it goes back together..

Does that make sense? I believe that would keep everything centered and be easy to do and doesn't require a bare block.

[Cuzzo]

Not a possibility to tilt the motor?

[TurboRA28]

Dont really want engine on 15 deg tilt either..
If it had to be one or the other I think i'd let the gearbox sit on the angle.. But I cant get to the oil filler bolt which is a shit. Can do some tunnel massaging if needed..
But ideally be nice to have everything sitting flat.

[Cuzzo]

Put the motor back in the camry?

I think if you cut and weld the bellhousing you would have to fill quite a few holes with weld. (not the strongest idea)

Custom bellhousing?

[wagonist]

I'm a little confused.

You're going to bolt the adaptor to the gearbox, and then the whole lot to the engine?
How do you access the bolts onto the block then.
From my thinking, you're going to have to drill new holes through the gearbox housing to access the bolt holes for the engine?

I think you need to bolt the adaptor to the engine first with countersunk bolts, and then bolt the gearbox to the adaptor.

An alternative would be to use studs in the engine block & then nuts to hold the adaptor plate on. Nuts would be shorter than the head of an allen key bolt.
It may be a PITA, but you could weld the adaptor onto the block which would assist in the thickness.

How far into the block do the gearbox bolts currently go?
How thick is the gearbox bellhousing where the bolts pass through?

I'd be using these measurements to determine your thicknesses and then use whichever is thicker. They've worked for Toyota for 30 years now.

ie use the gearbox thickness to determine the thickness of the plate from the block mounting face to the bolt. You'll then need to add on the countersinking part of the head.
Check to see if this overall thickness is larger than the depth the current bolts go into the block.
If not, increase it. Or use steel instead of alloy to make the adaptor plate.

Hope I make sense

[TurboRA28]

Nah plan was to bolt adapter to gearbox, then bolt bellhousing into the adapter.. So its all at the gearbox end, not the block end.

[wagonist]

By bellhousing, you mean the engine block, or the part of the gearbox around the clutch?

Just want to make sure there no confusion. Because we may be thinking of different things.

[TurboRA28]

This pic may explain it.. Not toyota bellhousing/box but the idea is the same..

[oldcorollas]

Joel, someone mentioned recently a good way to line it up...
machine a bar to sit in the engines main bearings in place fo the crank, with bit sticking out the back with ID so it slips over the input shaft... that way it is pretty hard to misalign... (if the bit sticking out is long enough, it will sort of remove any play in the input shaft)

thats if you wanna remove the crank..

[wagonist]

I was thinking of a sandwich plate between the gearbox & the engine, so a different execution (more commonly used for gearbox/engine in the same alignment but different bolt patterns), and what I was investigating for a 2GR-FE to E151F gearbox.

My theory is probably still the same though. How far into the rear casing do the current bolts thread? I'd use that as the basis of your adaptor thickness as you'll need to bolt the bellhousing onto the adaptor. Then just countersink the bolt heads enough so that they're not protruding.

If you're going to use allen key headed bolts, personally I'd also do the countersinking machining such that the heads are a snug fit into the hole. Under twisting (which is really what the bolts have to resist), the sides of the bolt heads are also being used to resist this movement, then giving you the full depth of the adaptor and not just the thinner part of the bolt shank.