Plugging Timing Case Holes

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jseng1 said:
You can get the right size brass hex pipe plugs from Mcmaster Carr with quick delivery.

1/4" brass hex pipe plugs #1491N187

1/8" brass hex pipe plugs #50785K112

Or make aluminum plugs and hammer them in. Use a drift with a larger diameter than the hole so you won't drive them in too far.

Plugging Timing Case Holes
Click to expand...

@jseng1 Those plugs were way too big. The holes are too small. 1/4" NPTF is not really 1/4".
 
Pipe thread measurements are determined by the ID of the screwed steel pipe that the thread was standardised for.

As you have discovered, the measurement itself be it 1/8, 1/4 etc has nothing to do with the physical size of the thread!
 
I would consider using a interference fit (no thread) plug with green Loctite at that cam bush location... if not done already and maybe even for both locations.
Those case holes are a lot different to the 850, well the one without those two extra holes.
 
Personally, cos those holes are a small diameter and deep, I think I’d just fill ‘em with a good silicone.

Make sure everything is good ‘n clean and spread the silicone out a little into a kinda of mushroom head on each side of the hole.

Can’t see it going anywhere.
 
We use metric grubscrews - and just drill and tap.

Where there is the case thickness to do so, I like to drive two in, one on top of the other - it stops any chance of them shaking out.

For ‘belt and braces’ we put them in with a smear of JB Weld, then centre pop the join between the threads.

No chance of them moving at all.

This is a Dommie case we’re currently building.

Plugging Timing Case Holes

Since you have got the bare cases, it’s the perfect time to do this job properly.

Don’t leave the holes open because you haven’t got the right screws to plug them - for a few cents and waiting a few extra days, it’s well worth the wait.
 
Last edited:
So on a 850 case.

Plug the three ports (2 x 12.5 mm / 1 x 9.5 mm aprox)
Plug the OEM oil return.
Drill a new 1/4" oil return down by the oil pump pad.
Leave the oil drain from the cylinder head as is.

??
 
New oil drain hole in timing case drilled (see previous video).

I was just hoping someone had plugged the holes and could tell me what they used. The McMaster part numbers earlier in this thread were pipe sizes and not useful. They don't seem to be standard size holes. Go ahead and try to find a 7mm set screw.

No chance in hell I'd stuff the hole full of silicone.

I'm going to try a 5/16 set screw for the oil return next.
 
Fast Eddie said:
Pipe thread measurements are determined by the ID of the screwed steel pipe that the thread was standardised for.

As you have discovered, the measurement itself be it 1/8, 1/4 etc has nothing to do with the physical size of the thread!
Click to expand...

So they used some sort of logic akin to how they came up with the Whitworth sizes
 
swooshdave said:
So they used some sort of logic akin to how they came up with the Whitworth sizes
Click to expand...

Dave,
Pipe thread is a completely different animal than a regular machine threads. One of the biggest differences is a pipe thread has a taper to allow the male and female parts to lock together. When a tapped mine out I did not run the tap completely through. I went far enough for the bung to lock into place and not protrude too far out on either side. Then I used JB weld and staked them in place. I forgot what sizes but I think they were 1/16” and 1/8” with brass grub screws.
 
I apologize to @jseng1, the smaller plug size worked ok. I suspect the larger one might work for 850s?

Plugging Timing Case Holes


This is just a test fit. I need to clean it all up. I can't see using locktite or JB Weld here. The tapered threads are going to hold it.

Plugging Timing Case Holes


The old oil return was pretty hard to tap and I didn't go as deep. Not worried about clearance like on the on by the cam.

Plugging Timing Case Holes


This one is a bugger. There isn't a lot of meat here. Again just a test fit. This one is going to get a bit of JB Weld. I don't like the cracking either.

Full video later.
 
Swoosh, like I said earlier, clean out that hole and fill it with Silicone! No cracking, no damage, no chance of grub screws coming loose...
 
@swooshdave as I mentioned on your Facebook post, I really don’t like what I’m seeing here.

A tapered plug will not fall in to the crankcase, but please confirm that you plan to carefully deform the junction between plug and tapped hole to stop it from backing out?

Feel free to plug from the other side where you feel there is not enough material to drill and tap.
 
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