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I have a 68 Cutlass S with a 4.1L inline 6 cylinder .Most of the spark plugs have a 13/16 hex and I need a 5/8 to fit the socket around the plug to get into the block. Does anyone know what plugs fit this engine?
Thanks
Glenn
Are the engine and the cylinder head definitely both original? Is the seat/seal area in the cylinder head flat and would use a gasket or is it tapered?
I'm working off of a phone at the moment but TSX is tapered seat. That head looks flat and would use a ring washer seal plug not a tapered plug. Somebody with better image access please jump in.
I don't understand why you need a 5/8" to fit the socket around the plug. I have changed plugs on second generation Chevy L-6's dozens of times with nothing more than a straight (non-ratcheting) 13/16" plug wrench on a 13/16" plug. 5/8" shouldn't even enter into the procedure.
I'm glad it worked for you but a 13/16 socket does not fit in the hole. Only a 5/8 deep socket will surround the hex in the hole. I'm not a mechanic but I know when something doesn't fit. I just came on here for some advice.
Around 1970 or 1971 Chevrolet switched from gasketed spark plugs to tapered seat spark plugs. That's why I asked if this is the original engine. If a 1968 car requires tapered seat plugs either the cylinder head or the complete engine has been replaced.
Give us a picture of the spark plugs currently in the engine, and a good close-up picture of the spark plug hole.
Are you making progress with this? The problem is it had the wrong spark plugs in it, seen it before. It had tapered seat plugs by the part number provided. It uses non-tapered plugs so the plug # you took out will not work. Try ACR45XLS.
Lets see some pictures of the car and a few standing back showing the engine bay with the econo 6. We don't see these often.
Is it a 3 on the tree trans?
Most people want to know when I'm going to replace the engine with an 8 ;-o .This one is one of 410 built with an inline 6, convertible. I like that its different.
Cool car. Bet not too many 250 Six 2 speed verts existed in 68 let alone today. The stainless steel wheel well trim would really set this car off.
To me that plug hole looks like its designed for a 13/16" hex gasketed plug not a 5/8" hex tapered plug.
Though it looks like a slight starter taper/chamfer exists as it goes down into the hole. Chamfering is a common machining practice. If it wasn't for that chamfer the tapered R45s would not have worked at all. Doubt that starter chamfer is the correct angle for a tapered plug.
You have to be concerned about the plug depth. Chevy commonly used 3/8" reach gasketed plugs in 68. 3/4" reach was for aluminum heads.
Tapered plugs in SBC started around the 71 model year.
Doing a little searching on various 250 web sites would agree with all of this. Id surf around and post the question or three if you need further validation, as I'm not a 250 Six expert.
AC R44XLS,NGK BPR4ES, etc are all gasketed plugs. A quick gander at Summit, plugging in the 250 Six resulted in gasketed plugs.
Yes, I believe it should have a gasketed plug. Its hard to see in the picture but it is flat so the gasket makes sense. The AC R45XLS looks like it might do the trick. Its always run a little rough and doesn't smoke at all so maybe the tapered plug that was in there made it run a little off. With new plugs and a timing reset, I'm hoping it will run smoother, though it doesn't run poorly at the moment. I may replace the plug wires too depending on how it runs. Couldn't hurt.
Confirm that the thread depth of the new plug is ok/correct. The R45 XLS is 3/4" reach, I just don't remember the 3/4" reach being correct but it has been decades since I've worked on one of them.
Three areas to check on that engine for idle problems:
Carbs get loose between the fuel bowl and the throttle plate,
Intake manifolds leak vacuum at the outer runners, and
distributor wear causing dwell/timing fluctuations. Move the dist shaft side to side to check and look for fluctuating vs rock steady base timing with a timing light.
Thank you for the compliment! I will try and find out the depth. If it was too long, would that cause any issues in the firing or maybe just burn less efficiently?
It could potentially hit a piston or valve. Look at how deep the threads are in the head before installing. The potential problem could occur if the head is after '73? or so, I'm not certain on the year the design changed. This engine is rare in Olds world and common in C___Y world. They were very durable engines.
If you search on Chevrolet six cylinder plug reach you'll find a ton of info about this at Steve's Nova Site.
Block is a 64-76 230 or 250 CID Chevy block. The head casting # is different than supplied, it should be raised and all numeric characters similar in format to the block.
Here are 2 pics on the right driver side headers . The small tag picture on the front passenger side of the valve cover gasket and is stamped K 725 but faintly behind it ( you cant see in the picture) are the code E then O or a zero,915TA. helpful? Thanks again for all the help. I do appreciate your time!
February 7th, 2024, 10:14 AM
