Spark Plug Question

[John P.]

I am changing plugs in a 67 L79 and am putting in AC Delco R45S and want to make sure I will not have any clearance issues with the pistons. They are slightly longer than the R45 I am replacing. Thanks in advance

[Lawrence M.]

Re: Spark Plug Question

You should have no problem with the R45S. I use them in my 1969 L46. Search R45S using the search function. Lots of info there.

[John P.]

Re: Spark Plug Question

Thanks Larry - I have reviewed quite a number of threads on the topic. I would appreciate another opinion or two on the R45S working without hitting pistons on a L79 application. Thanks again.

[Gene M.]

Re: Spark Plug Question

I use 44s in my 65 which does NOT have dome pistons and all is fine. The flame front is set a but deeper in the combustion chamber. But caution use with domes for clearance reasons.

What will the flame front do with domes and an extended tip plug? I don’t know.........

[John P.]

Re: Spark Plug Question

Alright - I quit being a wus and fired it up. No issues.

[Bruce W.]

Re: Spark Plug Question

John, I put a set of 45s in my 58 fuel car and they did indeed hit the piston and closed the gap. did no damage but did cause misfire. having said that I do not know what kind of pistons are in the car. the compression is 10 to 1 so I don't think the dome could be to large. why do you think you need the extended tips?
Bruce

[John P.]

Re: Spark Plug Question

Bruce,
I do have domed pistons in the car. I did not rebuild the engine but in reviewing the receipts for the rebuild they are a replacement for the original domed pistons of a 67 L79. To answer your question on the spark plugs, the car was not running well and I had completed about everything except for replacing the spark plugs. After a quick read of the NCRS forum and the Corvette forum, people were recommending the 45 S. Other than than what I read, I did not have an opinion on extended spark plugs or not. I bought them a few weeks ago and when I replaced them yesterday, I noticed they were a 1/4 or so longer and reviewed the forum again noticing most say I should not have an issue and few stated I might. I will say the replacement of the plugs eliminated my hard starting issue and the car ran great during the 20 mile drive I did. I will pull one this morning to see if they appear to have hit the piston.

I am still interested to hear from others to see if they work in a L79 configuration without hitting the pistons.

[Duke W.]

Re: Spark Plug Question

This "problem" is rather overblown. It's not likely to occur unless the block/heads have been significantly cut and a thin head gasket has been installed. You can measure the thickness of the installed gasket with feeler gages at the corners of the head-block interface. Most engines are rebuilt with thick composition gaskets that are about double the thickness of the OE .018" shim gasket.

Also, I believe the 462 heads that went into production in '67 have a slightly raised spark plug location, so the problem is even less likely to occur on these and later heads.

Duke

[John P.]

Re: Spark Plug Question

Thank you Duke for your response. I did pull one plug this morning and I do not see any evidence it hit the piston.

[Gene M.]

Re: Spark Plug Question

Thank you Duke for your response. I did pull one plug this morning and I do not see any evidence it hit the piston.

That is good information. Are you using the stamped steel head gasket or a composition type?

[John L.]

Re: Spark Plug Question

I am in the process of changing plugs and installing extended tip type plugs in my 66 L72. Given the helpful feedback from the DB and in speaking with the Champion Tech line, was advised there should be no clearance issues (engine rebuilt years ago, in stock condition except for slight cylinder overbore) My question, how would one detect if there are clearance issues? Would it be a function of poor driving performance, sound? Thanks for the feedback!

[Mark E.]

Re: Spark Plug Question

I never experienced it, but would expect awful mechanical noises for a second or two, followed by erratic running. Plug electrode can be checked to verify.

[John D.]

Re: Spark Plug Question

R45S spark plugs in my stock 67 L79 for over twenty years with no problems.