The Stovebolt Site Forums The Shop Area Engine Shop Spark plug type?

Finished priming the oil pump and was just about to put the new plugs in my rebuilt 292 when I noticed that they were clearly the wrong ones.

I bought Delco R44T - which is supposed to be correct. It's also what the core had installed when i bought it and sent it for rebuild.

However the holes are quite deep - an inch perhaps - with only the bottom 1/2 (piston side) threaded.

Interestingly, I happened to have R44XLS plugs "sitting" in the holes to keep things clean while she's been waiting - and they do appear to be about the correct length.

This is odd, because the XLS plugs came from a mid 60's 250 head, and as I recall my previous '84 292 did in fact take the 'proper' R44 tapered.

I know my head is later model because it has the A.I.R. ports at the exhaust.

However - it does have what appear to be torx head bolts which I've never seen on a 292.

Might I have some oddball head - maybe marine or agricultural - that requires a different plug?

Clearly I can't use the recommended plug - it's way too short and only engages a few threads.

Should I just go with the long R44XLS gasket plug and hope it runs well?

Any help appreciated.

I'll let an expert weigh in on this, but whatever you do - don't put in the wrong type without getting confirmation (by head identification & plug number or physical measurement) that you do not have an interference condition with the plug and piston...

Thanks. There's a metric boatload of clearance between the dished piston (at TDC) and the plug hole - literally inches, lol. so interference wouldn't be an issue. I presume the plug ideally will sit so the last (or first if you will) thread is flush with the combustion chamber face - neither recessed nor protruding - only the electrode protruding into the chamber.

This I can measure. Correct heat range? Trial and error?

The R44T would be recessed nearly half an inch looking at the hole from the combustion chamber side. Again - clearly not even close to correct.

..

Aside .. I wonder if this was the original reason this core went to scrap. Wrong plugs (somebody going by the book) either it wouldn't run, or got messed up.

Try an AC R44XL in it and see. Are the ports for the A.I.R system in the exhaust ports on the head, or the exhaust manifold?

Thanks for the reply.

The ports are on the head itself - looking down onto the back of the exhaust valve.

What is the difference between the R44XL and XLS?

Ah, got it. Found the AC numbering system. XL=3/4" reach, S=extended tip.

What does the seat look like? Gasket style plug or tapered seat? ARP seals a lot of torx style head bolts, never seen a GM engine with them. Does that head have a casting number?

Looks like a gasket seat to me. The long gasket plugs fit and as I measure should be the correct length. Just doing final checks and buttoning things up - hope to fill her with gas tomorrow and give her an initial up to temperature run.

IIRC the casting number is under the rocker cover. it's been a long road collecting the little hard to find bits and finally getting here, lol. Not up to taking the cover off again. Iknow it's only 7 bolts...

Had a surprise last night. I've never noticed the threaded hole under the rear lifter cover (about 3-4" in front of the oil sender port)- and apparently neither did the rebuilder.

Was priming the pump with a chopped up mid 60's distributor base and a gauge in the port - then white milky schmoo started coming out of this 'other' hole.

I guess it was assembly lube mixed with the new oil - but my first horrified thought was that the cam gallery was cracked. I nearly crapped myself.

My warranty expired years ago - whether she drove or sat on a stand.

An NPT plug and another go at the priming tool with a drill made 50 pounds at the gauge - so we're all good