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Discussion Starter · #1 ·
Started with a practice swing:
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Used spring loaded punch to make starting point:
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Hole is off center enough whereby I can't get 12mm socket onto the bolt even when angling the socket:
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It might make a good sight hole for checking cam chain wear:
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Another look:
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Bottom of the hole seems not to leave enough lip for a grommet to seal it and I don't see how one could effectively drill any lower or make the hole any larger.
The OD of my 12mm socket is 17mm or very close to it, typical for the 12mm sockets I looked at. I used the 11/16" step from the step bit.
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Not sure if I can salvage this procedure. Not sure the hole can be made so as to allow a blanking grommet to seal it at the bottom since there is little to no room for the lip of the grommet. I hit the center of the area where the cover had been milled with the punch or came darned close and the hole is still off. A millimeter or two to the right should center the hole if starting from scratch. In spite of my limited experience with such matters, I say that if the hole can be centered on the bolt and then effectively sealed I think this procedure superior to using an insert. However, given the precision required for centering the hole and questions related to sealing it, I'd say that this procedure is not yet ready for prime time.
 

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When I was considering this I arrived at this method for marking the position of the hole in the cover.

Take a hardened steel bolt the same thread as the tensioner mounting hole. Cut the head off and chuck it in your hand drill and spin it against a running bench grinder to get a concentric point.

Fit to engine block and adjust length until it is a mm or so too long to allow the cover to seat.

Fit cover with 4 8 mm bolts just nipped up. Assure same gap either side and top and bottom so cover is straight.

Tap cover with hammer over desired hole site.

Correctly situated punch mark for drilling.

May help somebody else.

Being in the US your best bet is a GL500 cover. TI with a manual tensioner and bolts straight on.

A further thought if you were to attempt this again. - Using aa allen bolt would mean you would only have to drill to the size of an allen drive - a smaller hole to seal and further away from where the cover 'decks' near the inspection port.

An allen bolt could still be an option. Maybe then you could JB weld a cut down nut over the hole that would allow clearance to insert an allen bit and then you could seal the resulting threaded hole with a short bolt and sealing washer?
 

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Another thought.

Get a piece of aluminium 5 - 6 mm thick.

Drill hole as pass through for allen bit and tap to next available thread size in preparation to be sealed with a bolt. An alan bolt will require the least clearance to the right angle of the cover.

Cut a section that will cover the area surrounding your hole..

File the back so that the contour matches the contour of the cover.

Abrade cover in fitting area and JB weld into place making sure the hole is centred. Having the allen bit in place will help, perhaps with a sleeve if you have something suitable.
 

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You beat me to it Mark, i had a similar idea.
 

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And 'ere I was thinkin only Aus and NZ knew the beanie.....
 

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I've also ground down the outside of sockets to accommodate small openings.
 
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Discussion Starter · #9 · (Edited)
Would it work if you enlarged the hole a size or 2?

Of course, the final size would need to suit an available blanking gromet size...
It would, but the problem is the efficacy of a blanking grommet given how close the bottom of the hole is to where the cover decks, that is, makes a 90 degree turn. It appears to me that as it is the lower lip of a blanking grommet would turn up and therefore leak.
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I've also ground down the outside of sockets to accommodate small openings.
Koken (Japanese brand) has a Z series of sockets specifically for tight auto spaces.....but grinding your own achieves the same end
 

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Discussion Starter · #13 ·
There are some good fixes here, but positioning and plugging the hole is yet too problematic to think of it as an alternative to using an insert.

Now that the relationship between the bolt and the cover is viewable I should be able locate with some precision where the center of the hole needs to be. I have some wellnuts similar to what are seen in reclinedrelic’s link that might work provided the head of the bolt does not interfere. I’d still need to widen the slot in the manual adjuster arm and make or buy a collar to accommodate the 8mm bolt but that should not present much of a problem.

I’m thinking if someone for some reason wanted to continue to use the 8mm hole (no insert), they could use a cap screw then thread and plug the hole found in the covers that are made for manual tensioners. The hole is certain to be centered, large enough for an allen wrench, and it appears that the area around the hole is thick enough for tapping and plugging or just plugging.

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Just a thought: I occasionally use 1/4" drive sockets when I need more clearance in a tight hole. The 12mm one's OD is about 1mm smaller than the 12mm 3/8 drive.

I wonder if a part to fit against the cover and accept something like the timing port cap could be made on a 3D printer? The problem would be finding a plastic that won't melt or get brittle.....

Of course, by the time you did that you might as well just change the cover.
 

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Discussion Starter · #15 ·
Just a thought: I occasionally use 1/4" drive sockets when I need more clearance in a tight hole. The 12mm one's OD is about 1mm smaller than the 12mm 3/8 drive.

I wonder if a part to fit against the cover and accept something like the timing port cap could be made on a 3D printer? The problem would be finding a plastic that won't melt or get brittle.....

Of course, by the time you did that you might as well just change the cover.
Of course, by the time you did that you might as well just change the cover.
Yeah, that's kind of where this is at.
 

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There are some good fixes here, but positioning and plugging the hole is yet too problematic to think of it as an alternative to using an insert.

Now that the relationship between the bolt and the cover is viewable I should be able locate with some precision where the center of the hole needs to be. I have some wellnuts similar to what are seen in reclinedrelic’s link that might work provided the head of the bolt does not interfere. I’d still need to widen the slot in the manual adjuster arm and make or buy a collar to accommodate the 8mm bolt but that should not present much of a problem.

I’m thinking if someone for some reason wanted to continue to use the 8mm hole (no insert), they could use a cap screw then thread and plug the hole found in the covers that are made for manual tensioners. The hole is certain to be centered, large enough for an allen wrench, and it appears that the area around the hole is thick enough for tapping and plugging or just plugging.

View attachment 210685
I was thinking a large set screw might work, since there's no flange. It would require sealant in the threads (wouldn't want crumbs of that in the oil), and there's not much depth there on the 650 cover. The deeper casting on the 500 cover might interfere with the larger bolt head.
 
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I wonder if a part to fit against the cover and accept something like the timing port cap could be made on a 3D printer? The problem would be finding a plastic that won't melt or get brittle.....
ASA would do it, I think. It's resilient like ABS, but UV stable. Not extremely heat resistant, but I don't think that part of the engine case would get hot enough to melt it.
 

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Pipe plugs are tapered and self sealing but don't know if there is enough threaded area for that to work.
 

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It looks like there might not be enough thickness for a full thread, let alone enough to hold. That's why I started thinking about a bolt on piece (similar to Mark's suggestion).

Re heat, I was thinking it is pretty close to the bottom of the cylinder. The issue probably wouldn't be the melting point but deterioration from being heated to the temperature of the cover repeatedly and for long periods.
 
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