Just for interest the welsh plug sizes (which aren't even listed in the workshop manual) are.
For the G150
1 1/4 inch for the 5 on the side of the block.
1 3/4 inch for the one on the back of the head.

MAN what a ball of information, didn't know all this stuff.

Thanks Pa man

With so many sizes about it's good info to have to replace weepy ones.

When I picked up the block I'm working on for group N from the machine shop I thought they'd installed new welsh plugs and happened to mention this. The reply was that just about every Isuzu motor they've seen has stainless steel ones. They just came up shiney after the wash and they looked like new once the black paint came off them. Reflecting build quality?

ohhh, i wouldn't believe that.... i'd still be putting brass ones in.
i put brass ones in my GT when i resto'd it, and they were definitly steel, because i've never seen stainless rust....

and even tho the aussie gemini engines were assembled here, they are still isuzu, and they were steel as well, as i've had one let go years ago.

cheers.

Had to replace 1 in Sid (661/2 sedan)after 44 years it was definately steel
Wonder if I can claim WARRANTY
Replaced with Brass
cheers Ken

Thanks for the advice PR91 and P.R.90

They certainly look like stainless but I'll do a close check on the insides. It's not nice when they let go but I thought factory fitted ones in good condition would be a better bet than home fitted new ones.

What's your opinion on "staking" new ones to limit the chances of them coming adrift?

Get the correct fitting ones put a smear of Stag compound on the edge & put in tight, should be good for another 40 years.Never had any trouble with ones I have fitted in the past .
Good Luck Ken

Thanks Ken
i won't go "overboard" on the installation then

i always replace them, with brass ones. there's no way i'd risk a 40yo steel plug, even if it looks OK on the outside.... it's the inside that rusts.
as PR90 said, some sealant, a well fitting socket to tap them in with (some they go in square), in flush or just past the face of the plug hole, and never had a prob.... ever.

ohh, and "blue RTV" gasket maker (blue goo!) works well too. is what i use.

Same here, on my V8's , 6's and 4's.

Cheers
Rob

maybe im wrong but i recall jamming a coin into a welsh plug in one of my cars to stop it leaking till i could fix it....
I can never recall fixing it after though....

the old penny used to work well i don't remember replacing the one I fitted to a sedan 20 odd years ago

Okay question to the knowledgeable, well maybe just the forum ;P
On the back of the block are 4 plugs, 2 water one cam now is the little 3/4 inch one into the oil gallery or is it water as well ?
The 2 I suspect to be water are the same 1-1/4 as the ones on the side of the block.

Cheers
Rob

You'd think welsh plugs are an easy thing to get

Have been to 4 different parts stores and still only have 4 plugs of the 7 i need sheesh.

Oh well I'll keep plugging away

Cheers
Rob