Parts Book recomendation for plug

[Jerry G.]

Does anyone know what plug the Chevrolet parts book calls for in a 492 head with straight seal. I tried a 1/2 reach NGK plug and it doesn't extend into the combustion chamber far enough. It's close but... Did Chevrolet have a recommended plug for this head? Jerry

[Gary C.]

Re: Parts Book recomendation for plug

Jerry, most plugs are listed by application; model and HP. Gary....

[Clem Z.]

Re: Parts Book recomendation for plug

Does anyone know what plug the Chevrolet parts book calls for in a 492 head with straight seal. I tried a 1/2 reach NGK plug and it doesn't extend into the combustion chamber far enough. It's close but... Did Chevrolet have a recommended plug for this head? Jerry

are your heads straight or angle plug heads ?? you can use a longer reach plug and use solid copper plug washers(spacers) to get the proper installed length. opps forgot you have tapered seat plugs

[Clem Z.]

Re: Parts Book recomendation for plug

looks like straight plug heads were 1970 LT-1 heads and the angle plug were OTC only. both used the same casting

[Jerry G.]

Re: Parts Book recomendation for plug

Hi Clem, my heads are straight seal. I have tried 1/2' reach and they fall about one thread short of making it into the combusion chamber. I guess I could go for longer than 1/2 and shim them but you would think Chevrolet had a plug in mind when they sold these heads? Do you know anything about TT plugs? Jerry

[Joe L.]

Re: Parts Book recomendation for plug

Does anyone know what plug the Chevrolet parts book calls for in a 492 head with straight seal. I tried a 1/2 reach NGK plug and it doesn't extend into the combustion chamber far enough. It's close but... Did Chevrolet have a recommended plug for this head? Jerry

Jerry-----


The '492' head when machined for gasketed type plugs was used as a SERVICE replacement for 69-70 high performance and special high performance applications (as well as earlier special high performance applications). The 69-70 applications used R43, R44 and R-45 plugs.

[Clem Z.]

Re: Parts Book recomendation for plug

i just measured a R-43T and it measures 1/2" from the top of the taper seat to the end of the shell. i would use TS plug which is the extended tip plug in that application and remove the threads in the head that show past the end of the plug to get rid of the "hot" spot caused by the exposed threads in the head.

[Jerry G.]

Re: Parts Book recomendation for plug

Clem/Joe I really appreciate you guys sticking with me on this. Joe the critical part of this was knowing that the recommended plug for a straight seal was the 44/45 series. They are 3/8 reach and will not work in these heads. When I look at these heads they are very different in the plug hole location. They are not angle plug but straight into the combustion chamber. I have two other sets of angle plug 492 heads and the spark plug thread opening will ONLY accept a small diameter tapered plug. The 492 heads I have are machined for both straight seal and tapered seal. I had not seen this before. The plug that works in these heads is a tapered seal plug as Clem points out. Even though the straight seal will go in and has the seating surface properly machined they do not work with a straight seal plug. At some point in the production and machining of the 492 series they must have moved away from machining for both and machined to just allow the tapered seat plug.
Clem I'm going out to get a set of the plugs you recommend today. I am a little curious still about the casting date on my 492 heads that we've been talking about. The casting is 3F17. I assumed that this was 1977 but my other angle plug heads are from 1973 and 72 and have a machined plug area that only allows the tapered seat plug to be used. Could these be a 67 casting or did they just machine both for over the counter non production ,service replacement heads so it would be easy to use either plug? Oh well, I have a working solution so I'm going forward. Thanks Jerry

[Terry M.]

Re: Parts Book recomendation for plug

I am a little curious still about the casting date on my 492 heads that we've been talking about. The casting is 3F17. I assumed that this was 1977 but my other angle plug heads are from 1973 and 72 and have a machined plug area that only allows the tapered seat plug to be used. Could these be a 67 casting or did they just machine both for over the counter non production ,service replacement heads so it would be easy to use either plug? Oh well, I have a working solution so I'm going forward. Thanks Jerry

I would assUme a 492 casting dated 3F17 = 1973 June 17 BWTFDIK

[Joe L.]

Re: Parts Book recomendation for plug

Clem/Joe I really appreciate you guys sticking with me on this. Joe the critical part of this was knowing that the recommended plug for a straight seal was the 44/45 series. They are 3/8 reach and will not work in these heads. When I look at these heads they are very different in the plug hole location. They are not angle plug but straight into the combustion chamber. I have two other sets of angle plug 492 heads and the spark plug thread opening will ONLY accept a small diameter tapered plug. The 492 heads I have are machined for both straight seal and tapered seal. I had not seen this before. The plug that works in these heads is a tapered seal plug as Clem points out. Even though the straight seal will go in and has the seating surface properly machined they do not work with a straight seal plug. At some point in the production and machining of the 492 series they must have moved away from machining for both and machined to just allow the tapered seat plug.
Clem I'm going out to get a set of the plugs you recommend today. I am a little curious still about the casting date on my 492 heads that we've been talking about. The casting is 3F17. I assumed that this was 1977 but my other angle plug heads are from 1973 and 72 and have a machined plug area that only allows the tapered seat plug to be used. Could these be a 67 casting or did they just machine both for over the counter non production ,service replacement heads so it would be easy to use either plug? Oh well, I have a working solution so I'm going forward. Thanks Jerry

Jerry-----

The heads could not be 1967. The '492' casting had not even been "invented yet" at that time. Besides, the date is most probably June 17, 1973. However, it could be 1983, too, since this casting was still being produced at that time.

I know of no '492' heads that were machined for both gasketed and tapered seat plugs. They were machined for one or the other. The thread lead-in chamfer on a gasketed plug head may APPEAR to be a seat for a tapered seat plug, but it's not. In fact, if you look at heads manufactured well before the tapered seat plug was invented you will find the same configuration. If a head is machined with the large spark plug counterbore, that head is intended for gasketed plugs.

However, let's assume for the moment that the heads you have were intended for both tapered seat and gasketed plugs. If that were the case, then either type of plug should work just fine but you're advising that the gasketed type are too short. So, that would say that they were not intended for gasketed type plugs. But, they have the large spark plug counterbore. This amounts to a "non-sequitur".

[Jerry G.]

Re: Parts Book recomendation for plug

I agree but ..i put a AC43TSX in the head and it ends exactly where you would expect in the combusion chamber. I can send photos if it would help. Jerry