Hole Size

[myoldjalopy]

Hello peeps,
I want to make a hole in the bulkhead of my car to take a grommet that has an inner diameter of 11mm (it is actually a speedo cable grommet but I want to route some screen wash pipes through it). The actual hole will have to be bigger than the 11mm inner diameter, but how much bigger so that it is a snug fit but not scrunched up in the hole?

[panky]

I can't give an accurate answer but as you're using the same grommet you could measure the speedo cable hole that's already there . A step drill is you friend for this.

[Bill_qaz]

Dont you have caliper or vernier and measue the diameter. If not use string to measue circumference and calculate the dia.

[myoldjalopy]

I can't give an accurate answer but as you're using the same grommet you could measure the speedo cable hole that's already there . A step drill is you friend for this.

Yes, I did think of that but trying to work things out from the comfort of my settee! I do need to replace the speedo cable anyway but haven't got it yet. I want to do both jobs concurrently.

[myoldjalopy]

Dont you have caliper or vernier and measue the diameter. If not use string to measue circumference and calculate the dia.

No, I don't, but string will give an idea. I dared asking AI, specified the Minor speedo cable hole and it said a 13mm hole, which sounds plausible........

[myoldjalopy]

Ah, no I don't trust AI! Using the string method, I get a diameter of 17mm, which looks likely when comparing to the diameter of the inner 'step' of the outside of the grommet as measured with a ruler....Maybe measuring the existing cable diameter is going to be safest....I don't want to make a hole and find its too big or too small..

[bobtail4x4]

you can always make a small hole bigger,

[Bill_qaz]

Ah, no I don't trust AI! Using the string method, I get a diameter of 17mm, which looks likely when comparing to the diameter of the inner 'step' of the outside of the grommet as measured with a ruler....Maybe measuring the existing cable diameter is going to be safest....I don't want to make a hole and find its too big or too small..

Always trust string and maths over AI

[myoldjalopy]

you can always make a small hole bigger,

Yes, true, but I don't want to buy multiple bits just to make one hole!

[bobtail4x4]

buy a step drill

[svenedin]

Isn’t a speedo grommet a bit big just for screen wash pipe? The Speedo cable hole in the bulkhead has to be big enough for the speedo connector to pass through. It’s actually a considerably bigger hole than is needed just for the diameter of the cable. My screen wash pipe goes through the same grommet as the electrical wire (it’s an electric washer pump). I’ll take a picture tomorrow.

Stephen

[myoldjalopy]

buy a step drill

Now there's a thought! I never heard of one until Panky mentioned one!

[svenedin]

Here is a photo of the washer pump pipe going through the bulkhead along with the electrical wire for the motor. This is a brake pipe grommet, the same as the grommet where the metal brake pipe goes through the engine bay floor. Also a picture of speedo cable and grommet

Stephen

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IMG_2697.jpeg (2.89 MiB) Viewed 35128 times

[myoldjalopy]

Thanks for the pic, Stephen. The thing is, I need to get two pipes through (one from the bottle in to the manual pump, and one out again to go to the 'squirters'. I thought one hole in the bulkhead would be better than making two of them. Also, I already had a spare speedo grommet knocking about so thought I might as well use that.

[svenedin]

I don't really understand that. There's one pipe that goes through the bulkhead from the bottle. That pipe goes to one side of the manual pump. Another pipe exits the manual pump, behind the dashboard and goes to the washer jets via a nylon T-piece. All of this is behind the dashboard. My car had squirters from the factory but they were manual. By the time I had stewardship, my car had an electric pump but the plumbing is very similar to what it would have been (including the correct green tubing even where you can't see it).

Stephen

[myoldjalopy]

Ah, but my squirters are located on the bonnet, so the pipe has to come out again!

[svenedin]

Ah, but my squirters are located on the bonnet, so the pipe has to come out again!

Totally barmy but I see the issue.

Stephen

[Bill_qaz]

Ah, but my squirters are located on the bonnet, so the pipe has to come out again!

In that case why not fit an electric pump under the bonnet, then only the switch wire needs to pass through bulkhead to the switch and can share one of the existing grommets all pipe work would stay under the bonnet.

[myoldjalopy]

That would, indeed, appear to be an elegant solution - but I'm not too sure about these new-fangled electric pump gizmos!

[Bill_qaz]

Never had issue they are cheap and pretty reliable but I don't use it anywhere near as much as modern car as the small screen doest seem to get as dirty.

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