compression for 4 cylinder db

[nearchoclatetown]

what should compression read on a gauge for a 4 cylinder db? is there some trick to getting stainless valves to seat? and why does my brand new $68 headgasket leak antifreeze to the outside of the engine?

[Guest Stllrng.]

Off hand I am not sure what the cranking pressure would be on your Dodge, the most important thing is for them to be even. As for the stainless valves, they have to be ground and seated in like any other valves. It should be no problem. If your new head gasket is leaking, it is unlikely that the head gasket is at fault, it is more likely that the head is warped and needs to be ground, or the block needs to be decked. Check both with a straight edge and feeler gauges. You may also have a cracked head or block. I hope this helps.

[nearchoclatetown]

thanks, i had the head surfaced, no cracks. the gasket weeps collant several places around the outside. the compression is evan but seems low, 45 psi.i was told by another db member 50 is ok. still seems low. with low compression ratio of db's will gauge reading also be low?

[Guest]

The 1915-1927 Mechanics' Instruction Manual states for compression: 50 to 55 lbs. at cranking speed, 65 lbs. at 470 R.P.M.

[nearchoclatetown]

thank you that makes me feel better. didn't find anything in book of information except description of the four cycles . there it says during compression stroke engine gets about 65 psi charge. thanks for your input.

[MrLiken]

If you find the source of your leak, would you let me know. My 15 touring also leaks from the new head gasket. I have been very careful in torquing down the head bolts, because there is no real reference for the amount of torque to use. The mechanics manual says to draw it tight or something to that effect, without giving a measurement.

Thanks, John

MrLiken@aol.com

[Guest]

This is John B. I havent figured out how to register on this new site yet. Is this new gasket you are using made of that modern gray or tan material, or is it the old copper sheets with asbestos between? If the new stuff, there is a break-in sequence to use. We published this in a club issue about 6 mos ago. I believe you warm up the gasket, let it sit overnight, and then retorque and then retorque yet again. The new stuff has to take a set. Tom Hannaford of Antique Auto Parts Cellar sent us that seating information and maybe he has a website with more specifics. Otherwise go back to the seller of the gasket for instructions.

[nearchoclatetown]

thanks for responses. compression seemed too low at 45psi. the new gasket was the copper one but it was pretty beat up, so i used permatex on both sides. since getting it running yesterday the dripping around the edges seems to have stopped. it pulls both steep hills going to my neighbor's house in high gear. and i can stall the engine by holding my hand over the exhaust. so i guess it's ok. most of my knowledge is from the 60's and 70's having a hard time adapting.

[MrLiken]

Did you find a compression tester that screws in, or did you use the rubber base?  I'm not having any luck finding one with the large threads.

 

Thanks,

John

[Mattml430]

You can buy adapters to take normal size plugs. Best to use one of them. 

You’ve found a post when Doug was a young man well done. 😂

[DB26]

I took an old antique spark plug, (the kind that unscrews into separate pieces allowing the porcelain to be removed) and tapped threads into the bottom portion allowing me to essentially have an adapter that goes from the original size to the size of the tester. Works great! 

[nat]

On 9/8/2002 at 12:45 AM, MrLiken said:

I have been very careful in torquing down the head bolts, because there is no real reference for the amount of torque to use.

     The torque spec for later flathead engines with 7/16-20 threads is 55 Ft./Lbs.

On 9/15/2002 at 7:55 PM, nearchoclatetown said:

the new gasket was the copper one but it was pretty beat up, so i used permatex on both sides. since

     A gasket between two clean flat surfaces should make a seal.  IF sealer is used on a head gasket, (for these engines), it should be used sparingly around coolant ports only and/or to fill a specific blemish.  Great care should be taken to keep it off of the cylinder seal area.

     

[Mark Gregush]

On 8/14/2023 at 12:46 PM, MrLiken said:

Did you find a compression tester that screws in, or did you use the rubber base?  I'm not having any luck finding one with the large threads.

 

Thanks,

John

The Model A Ford parts suppliers like Snyders Antique Auto Parts should have one. (an adapter to use with standard compression gauge)

Edited August 25, 2023 by Mark Gregush (see edit history)