Spark Plug size??

[Anonymous]

I can't believe I haven't been able to get a straight answer on this at the auto parts store... they told me spark plug sizes are only 5/8 and 13/16... well I tried both of those and they don't fit. I think the right size is 18mm so I bought a socket kit... and it includes every size but that one!!!! (No joke, sizes 10-17mm, and 19mm)

Is 18mm the right one?

For a GS650G!

One more question.... what size of compression tester should I buy that will fit?

Thanks! You guys/gals are the best for someone like me just starting out with no clue what I'm doing!

[Anonymous]

The auto parts store guys are idiots (no offense)
I believe it's 3/4, but I'm not at home to verify. Your 19mm might fit, but tight.

Compression tester...Waddya mean, what size? To screw into the head? IIRC, it's 14mm, best to take a plug to wherever you get the tester. Some you don't even screw in, they have a rubber tip that you put in the hole and hold in place.

[Anonymous]

I tried the 19mm and was able to get the plug out, but it was loose... I thought I was going to strip it.

Bad news, the plugs look pretty bad... wet and black! The manual says that could mean the pistons or valves or wearing.... but then again, the bike was sitting for a few years.

[daveo]

It's actually an 18mm, I took a regular deep well socket and put a piece of fuel line in it to cushion the ceramic

[satchmo]

Had you ran the bike recently? Was the plug wet from Gas or Oil. Gas could mean you're running to rich, or could be ignition problems.

Oil fouled plugs are out of my league.

Satch

[Anonymous]

It looks like oil fouled plus. not gas... but thats just a guess.

I bought a used compression tester... and it doesn't fit.. even the small threads are too big. I thought it was 18/14mm .... maybe it's an imperial size???\

So I went to the store to look at new ones, and I brought the plug... it's really hard to tell if a 18/14mm will fit. And the guy says if I open it, I can't return it!!

[bostrom155]

It looks like oil fouled plus. not gas... but thats just a guess.

I bought a used compression tester... and it doesn't fit.. even the small threads are too big. I thought it was 18/14mm .... maybe it's an imperial size???\

So I went to the store to look at new ones, and I brought the plug... it's really hard to tell if a 18/14mm will fit. And the guy says if I open it, I can't return it!!

I was wanting to get a compression tester too, is the 82 gs11e an 18mm. the only tester they have at harbor frieght was a 14/18, just hoping its an 18mm that screws in. I know it's a 18mm socket, but what about the hole???

[bostrom155]

Just wondering if anyone has bought a 14mm/18mm compresion tester abd if it fits the 82 gs11e

[Tom MLC]

Your spark plugs use an 18mm socket. It's not the same as a car, and those bozo's at the auto shop don't know that. Now you are smarter than they are!

Motion Pro sells a compression tester complete with 3 hoses to fit 10/12/14mm spark plug holes. One of them will fit. I think its the 12mm.

[cberkeley]

It's actually an 18mm, I took a regular deep well socket and put a piece of fuel line in it to cushion the ceramic

18mm it is, I did the same with a deep socket, I epoxied the fuel tube inside as a cushion.

[cberkeley]

I broke an old plug apart and silver soldered some brass fittings to it to fit my compression tester. Works like a charm!

[crusin550]

Would 18mm be the same size for my 85 GS550L plugs? I only have a 5/8 spark plug socket and it doesn't fit. Auto store only has 13/16.

[madjack57754]

I'd find a real parts store. The kind where the counter guy is the store owner. CKS, autozone, kelly, and the rest of those fast food chain type parts stores are useless. If it's not in their computer It doesn't exist. I've been asked make model and year, when I was looking for a square bore holley base gasket for a 32 ford roadster with a smallblock chevy. That really confused the pimple behind the counter

[chuckycheese]

12 mm reducer

That seems odd that the auto parts people wouldn't know such basic information. I think most auto parts stores sell motorcycle spark plugs...at least the ones around here do.8-[

[bwringer]

You can get an 18mm spark plug socket from any Sears.

This size is common on bikes, but is pretty much not found on cars. I wouldn't really expect an auto parts store to have one of these sockets.