340 Compression Readings

[7212Mopar]

 

not gonna put it on an engine stand?

No sir. I had to lift the heads off and try not to hurt my back at the same time. Will need to do the same to put the new ones on. Cleaning is done so need to order instruments to measure, fingers crossed.

[7212Mopar]

I am done cleaning the engine block surface and the carbon deposit on the pistons. I still need to order some tools to do measurements. Assuming the pistons are indeed .018 above deck and going with the RHS close chamber heads, I will need a head gasket thickness of about .058 to get .04 quench.  Here is what I found today searching for the head gaskets.

1. Fel-Pro 8553 PT composite gasket that one of the member here had used on a project very similar to this. It is suppose to be around .054 in thickness. However, I found a response on the net from Fel-Pro indicating the thickness is .04 which there are many gaskets available at this thickness. I could not find any official specification from Fel-Pro and the major parts stores also have no information. May be I should buy a set and torque it down and then measure? It is less than $20 a set. Fel-Pro does makes 8553SP which is a soft copper shim with a thickness of .02. Together with the head gasket, the como will yield .06 in total thickness. Has anyone use a shim for cylinder heads to build up thickness? I wonder how long it will last before leaking.

2. I did find MLS gasket in .06 thickness which should work. My concern is that MLS gaskets suppose to require smooth freshly machined surface which my engine block will not be. The block surface is not rough by any means but I have no idea what the RA number is. Have anyone use MLS gasket in a head replacement project without touching the engine block?

Please share your thoughts.

[cudabob496]

can't you rough up the surfaces with some sandpaper or emory board,
beging careful to not let debri get down in the rings.

So the gaskets all compress to a different thickness, correct??

[7212Mopar]

can't you rough up the surfaces with some sandpaper or emory board,
beging careful to not let debri get down in the rings.

So the gaskets all compress to a different thickness, correct??

I got the technical info from this article

http://www.enginebuildermag.com/2014/10/upgrade-performance-head-gasket/

BTW, Hughes Engines website list Fel-Pro 8553 PT to be .054 thickness. I think I am going to write to Fel-Pro to confirm. I don't understand why their website don't list the official specifications for their products.

[jimynick]

Before you get too wound about gasket thickness, may I suggest you check to see what the actual piston/deck relation is? Buy or borrow/rent a straight edge and set it across a hole, run up the piston to TDC and measure it. If it lifts the straight edge you can confirm the height by buying a cheap .018" feeler gauge, cut it in 2 and shim the edges of the straight edge. It it all shows square then, you've confirmed it. Alternately, if the piston doesn't touch the straight edge, then you know you've got some latitude in gasket selection. gaskets aren't cheap any more and you may as well get the one that'll do the job. Just my 

[cudabob496]

Before you get too wound about gasket thickness, may I suggest you check to see what the actual piston/deck relation is? Buy or borrow/rent a straight edge and set it across a hole, run up the piston to TDC and measure it. If it lifts the straight edge you can confirm the height by buying a cheap .018" feeler gauge, cut it in 2 and shim the edges of the straight edge. It it all shows square then, you've confirmed it. Alternately, if the piston doesn't touch the straight edge, then you know you've got some latitude in gasket selection. gaskets aren't cheap any more and you may as well get the one that'll do the job. Just my 

Would think that when engine is hot and running, all these piston/deck dimensions would change some?

[7212Mopar]

Thanks Jimynick. I ran my fingers over the piston top and deck and knew the pistons are above deck. I did use a metal ruler from a square and feeler gauge as suggested by Cudabob earlier. With Timing mark at TDC and measuring piston 1, I had .014 left side, .012 right side, 0.014 top and bottom of the piston above deck. I might not be holding the ruler steady. I am waiting for the degree wheel kit and the magnetic deck bridge to arrive in order to find TDC accurately and to measure multiple points on couple of the pistons to get a more precise picture.

[jimynick]

Are we talking about the same thing here? What part of the piston is above the block? If it's a dome that's one thing, if it's the base of the piston crown at the top of the top ring land, that's another. In other words, if the whole circumference of the piston is .014" out of the whole, I see your dilemma. Good idea to buy the tools mentioned. Don't forget a piston stop, to help find that TDC as it's easier to set the head back on for the measurement than trying to allow for timing chain stretch when using a degree wheel and only using a dial indicator. Remember that the piston dwells at TDC for a certain # of degrees before moving, either up or down. Have fun. 

[7212Mopar]

The pistons are flat top with valve reliefs. The ruler was placed on the flat top surface of the piston and it is above deck.

I had some email exchange with the RHS heads dealer. He recommended the heads to be machined from 62cc to 68 cc to bring compression to around 9.75 for pump gas. Only 91 octane gas in CA. So the head package cost went up quite a bit. It might be easier for a novice like me to just go with the open chamber Edelbrock 340 heads. For sure no problem finding head gaskets.

[Chryco Psycho]

I would not touch the Eddy heads , went through 6 sets trying to find the best set with minimal core shift , QC sucks

[HP_Cuda]

The Eddy heads are also a pain when it comes to exhaust since the head sits a bit lower than a normal head.

[moper]

With those pistons you're better with the RPMs.
Here's a few thoughts as to why:
The block is not machined smooth enough for a decent seal with MLS gaskets (Cometics).
The closed chamebr RHS heads will need to be asembled - they only come bare so you're buying all new valves, springs, retainers, locks, and seals.
The RHS heads require rockers which while available are not cheap.
If you thought the factory heads were heavy - the RHS heads are heaviER becayse they have multiple rocker designs cast in.

All in all I think you'd do better to get some open chamber RPMs, run the Felpro 1008 gaskets, and have the valve job checked and corrected. Ignore any quench thoughts - you need to have a close fit and I think it's a waste of time given the pistons you have. You won't giving up much, and it will run great on any pump swill.

[cudabob496]

The Eddy heads are also a pain when it comes to exhaust since the head sits a bit lower than a normal head.

Someone better tell Eddy, so they can clean up their act!

[Chryco Psycho]

I am done cleaning the engine block surface and the carbon deposit on the pistons. I still need to order some tools to do measurements. Assuming the pistons are indeed .018 above deck and going with the RHS close chamber heads, I will need a head gasket thickness of about .058 to get .04 quench.  Here is what I found today searching for the head gaskets.

1. Fel-Pro 8553 PT composite gasket that one of the member here had used on a project very similar to this. It is suppose to be around .054 in thickness. However, I found a response on the net from Fel-Pro indicating the thickness is .04 which there are many gaskets available at this thickness. I could not find any official specification from Fel-Pro and the major parts stores also have no information. May be I should buy a set and torque it down and then measure? It is less than $20 a set. Fel-Pro does makes 8553SP which is a soft copper shim with a thickness of .02. Together with the head gasket, the como will yield .06 in total thickness. Has anyone use a shim for cylinder heads to build up thickness? I wonder how long it will last before leaking.

2. I did find MLS gasket in .06 thickness which should work. My concern is that MLS gaskets suppose to require smooth freshly machined surface which my engine block will not be. The block surface is not rough by any means but I have no idea what the RA number is. Have anyone use MLS gasket in a head replacement project without touching the engine block?

Please share your thoughts.

 Yes I have used Cometic MLS gaskets on an untouched block , it may seep antifreeze  slightly but after a couple of heat cycles it will seal up fine , you can use a sealer like iron tight in the coolant or copper coat on the gasket also  .
 I will not run any alum head without an MLS gasket , any other gasket is a failure waiting to happen , alum expands at almost 2x the amount as steel so it works against the gasket expanding & contracting with every engine start .

[74 challenge]

Yes I have used Cometic MLS gaskets on an untouched block , it may seep antifreeze  slightly but after a couple of heat cycles it will seal up fine , you can use a sealer like iron tight in the coolant or copper coat on the gasket also

I second MLS gaskets with Copper coat.

worked like a charm on every engine I have ever done head gaskets on. From jap crap to SBC's.