Question is answered: 273 Engine Block Decking

[Deleted member 38666]

Need more help. I bought a 273 Hipo rebuild kit from Falcon Performance to rebuild my 273 2bbl 4-valve relief piston engine. The HiPo Pistons are manufactured by Packard. The machine shop said it is common, on these old engine blocks whether Mopar, GM, Ford, or whatever, that the tolerances are not as truly accurate as modern day machining. Anyway, they told me, prior to boring the bock to the 0.030 over, that the block needed to be decked at 0.015. I am using the aluminum cast pistons from Falcon Performance/Packard as previously described, and the heads HAVE NOT been planed. I am installing a Racer Brown 210 duration/.430/.430 lift cam with OEM valve springs, solid lifters, and OEM rockers on the 273 un-planed heads. The new Pistons have the 2-valve relief half dome, and the Felpro head gasket has a thickness of 0.057. My question is, with the 0.015 block decking, will I have valve to piston clearance issues regarding the described parameters. I do not know if Falcon Performance HiPo Pistons built by Packard are manufactured to OEM height, but, assuming they are, with a 0.015 block decking, no head planing, and the higher lift cam, will I have a collision between the valves and pistons. I think I have all the info listed, but if I forgot something, ask away. Appreciate your help greatly. Thanks for the help. Old Dart 66

 

[pishta]

Are your heads open or closed chambered? There has been some debate on whether the 4v pistons are clearanced for closed chambered heads but IIRC, they will clear on a stock block. .015 is really just a clean up cut so Id say no problem but you can always mock it up prior to torquing. Lay the heads on without head gaskets and 1-2 head bolts snugged and rotate the crank 2 revolutions to see if it binds. If Packard is the same Packard that made cars back in the 40's, they were the only car maker in US that Rolls Royce deemed able to produce the Merlin V12 motor due to its very tight tolerances.

 

[70aarcuda]

most blocks are not square....but I would not just cut it .015 on deck...I would want the block squared.

Usually you are shooting for a zero deck on your piston deck clearance whereas went the piston is at TDC is it even with the deck of the block....In doing that you need to add 1/2 the stroke of the crank..plus the length of the connecting rod and plus the Compression height of the piston....this number is given to the machine shop and that what the deck is cut too...the blocks are uneven left and right and front to back....what is you want is it squared.

With a LA block you are usually shooting for a 9.599 deck height...but you can have him square the deck but only take a minimal amount off.

you might want to ask what kind of machinery he uses to square the deck...

 

[Deleted member 38666]

Are your heads open or closed chambered? There has been some debate on whether the 4v pistons are clearanced for closed chambered heads but IIRC, they will clear on a stock block. .015 is really just a clean up cut so Id say no problem but you can always mock it up prior to torquing. Lay the heads on without head gaskets and 1-2 head bolts snugged and rotate the crank 2 revolutions to see if it binds.

Hi Pishta. Thank you for your response. I am not much of a mechanic, so I am sorry that I do not know the difference between open and closed chambers. I will say that the heads have a bit of a recess where the valves will open and close. These are stock 273 2bbl heads from a 1966 Dodge Dart. I will do what you described for a test. Also, I do not know if this block has ever been decked before, but, after I removed the heads, during dis-assembly, I turned the crank, and the pistons did not reach the top of the block deck. All eight were slightly below the deck. Thank you for your time. Old Dart 66

 

[pishta]

Zero deck is not going to work with those 4v pistons as they are pop ups IIRC, or very close to it..

OldDart 66, closed heads chambers are not circle shaped when you look at the bottom of the head, they are heart shaped or D shaped. Opens are full circle. The domes on the 2 valve relief pistons are opposite the valve side so they 'fit' into the head on those motors.

 

[70aarcuda]

If the machine shop just goes in a cut .015 off each side...any irregularity from left bank to right bank and front to back will still exist....

So you just wasted your money....but it is your money...lol

 

[Deleted member 38666]

most blocks are not square....but I would not just cut it .015 on deck...I would want the block squared.

Usually you are shooting for a zero deck on your piston deck clearance whereas went the piston is at TDC is it even with the deck of the block....In doing that you need to add 1/2 the stroke of the crank..plus the length of the connecting rod and plus the Compression height of the piston....this number is given to the machine shop and that what the deck is cut too...the blocks are uneven left and right and front to back....what is you want is it squared.
With a LA block you are usually shooting for a 9.599 deck height...but you can have him square the deck but only take a minimal amount off.
you might want to ask what kind of machinery he uses to square the deck...

Thanks 70aar, Too be honest, I do not know what kind of equipment that they use, but their machine shop is roughly 30,000 square feet covered with equipment. They turn cranks that are over eight feet long that are for ship engines. They did check for square as I was informed. I don't know beans about engines....just learning. Yes, I thought 0.015 was a bunch, but what do I know....Not too much. With the talent in that shop, I would guess that they have the resources to check on tolerances and clearance, but who knows as I have assumed before in my life....and at times it comes back to bite me. That is why I am asking, and I appreciate your input. I suppose I should get in touch with Packard to see if the Pistons are built to OEM height. That would, probably, be a good place to start. I will say, though, that the shop has the pistons, crank, rods, heads, and all bearings along with the block in their shop. Maybe it was just for my personal FYI that the owner stated that they were going to deck the block at the 0.015. Thanks for your help. Much appreciated. Old Dart 66

 

[Deleted member 38666]

Zero deck is not going to work with those 4v pistons as they are pop ups IIRC, or very close to it..

OldDart 66, closed heads chambers are not circle shaped when you look at the bottom of the head, they are heart shaped or D shaped. Opens are full circle. The domes on the 2 valve relief pistons are opposite the valve side so they 'fit' into the head on those motors.

View attachment 1715164220

Thank you for the ID. Yes, the engine was an original 4 valve relief piston, 2bbl 273, and I am rebuilding the engine to the 273 HiPo with the 2 valve relief HiPo Pistons. Now, with your explanation, I get the difference. Thanks. On the 1966 273 engine that I am rebuilding while looking at the bottom of the heads, the valves appeared to be recessed into a wedge appearance constuction. The mechanic who is helping me build the engine, or should I say, I am helping him, has been using this machine shop for years, so I think I will be OK. Just had the question about clearance. I have a call in to Rich Moore at Packard who makes the HiPo Pistons for Falcon, and he will give me the info on OEM piston height. I will post that information on this thread tomorrow. Old Dart 66

 

[rustycowll69]

I don't know how much you can check when all the parts are at the machine shop. If it were me, I'd have checked each rod for center to center length. Now if you picked the longest rod, you could match it with the tallest piston to simulate worst case scenario. I'd temporarily bolt up the piston rod assembly in #1,#2,#7,& #8 holes and measure the deck height. From the measurements you can infer the out of plane difference for each head mounting surface of the block, ASSUMING each crank throw strokes are consistent and spot-on.
As for pistons hitting valves, it is much more complex and there are many other factors to consider like cam specs cam timing, etc. You are really concerned with like 20 degrees before but mostly after TDC. This is where many guys use a ball of clay to take an impression representing the physical valve to piston clearance inside the combustion chamber at the minimum clearance position. It is relatively quick and very visual. But it entails a lot of prep work, mocking EVERYTHING up, making an impression and depending on the results, tearing it back down to correct a problem, or reassembling to try it on another cylinder, etc. This can be done ad nauseum until you're satisfied with the clearances.
This is a lot of work to expect from a machine shop, that's why I do my own assembly and some of the machine work, because I can only trust my work, and that's the only kind of work like that that I can afford.

 

[Deleted member 38666]

I don't know how much you can check when all the parts are at the machine shop. If it were me, I'd have checked each rod for center to center length. Now if you picked the longest rod, you could match it with the tallest piston to simulate worst case scenario. I'd temporarily bolt up the piston rod assembly in #1,#2,#7,& #8 holes and measure the deck height. From the measurements you can infer the out of plane difference for each head mounting surface of the block, ASSUMING each crank throw strokes are consistent and spot-on.
As for pistons hitting valves, it is much more complex and there are many other factors to consider like cam specs cam timing, etc. You are really concerned with like 20 degrees before but mostly after TDC. This is where many guys use a ball of clay to take an impression representing the physical valve to piston clearance inside the combustion chamber at the minimum clearance position. It is relatively quick and very visual. But it entails a lot of prep work, mocking EVERYTHING up, making an impression and depending on the results, tearing it back down to correct a problem, or reassembling to try it on another cylinder, etc. This can be done ad nauseum until you're satisfied with the clearances.
This is a lot of work to expect from a machine shop, that's why I do my own assembly and some of the machine work, because I can only trust my work, and that's the only kind of work like that that I can afford.

Indeed, therefore, the question. Just asking for opinions as the machine shop built the heads, turned the crank, is boring and decking the block. Just asking, since a professional mechanic and I will be assembling the engine, and I was curious about possible clearance issues. Absolutely, we will mock up prior to firing it up. Thank you. Old Dart 66

 

[pishta]

To clarify, the '4v' pistons is more of a Ford term to represent a 4 barrel application, so I should have called the high compression pistons " 2 relief pistons " Carry on....

 

[pishta]

post up that Falcon Performance 273-4 kit link. I couldnt find it.

 

[MOPAROFFICIAL]

Meaure the deck from the main saddles, rods can vary in length after resizing.

Most blocks are off about .003-.008 front to rear, so they need attention... also that will translate to intake fitment a small amount..

 

[Deleted member 38666]

post up that Falcon Performance 273-4 kit link. I couldnt find it.

Thanks, I do not know how to post up a link, but I bought the rebuild kit number1847-300 through Falcon Performance. When I was looking for a rebuild HiPo kit for the 273, I typed that information in, and Falcon Performance came up. Thanks for your help. Much appreciated. Old Dart 66

 

[Krooser]

Apparently Packard Industries is part of Kanter Auto parts and Egge builds the pistons in CA

 

[ddartdude]

Hi Pishta. Thank you for your response. I am not much of a mechanic, so I am sorry that I do not know the difference between open and closed chambers. I will say that the heads have a bit of a recess where the valves will open and close. These are stock 273 2bbl heads from a 1966 Dodge Dart. I will do what you described for a test. Also, I do not know if this block has ever been decked before, but, after I removed the heads, during dis-assembly, I turned the crank, and the pistons did not reach the top of the block deck. All eight were slightly below the deck. Thank you for your time. Old Dart 66

Use the 2bbl heads as they are. They should be the 920's with 1.78 and 1.50 valves. My D/Dart ran a best of 12.95 and 105 mph back in 1966 with bone stock heads. So they should be good flowing. After all they are a swirl port design. I'd just do a good 3 or 4 angle valve job on them.

 

[AJ/FormS]

IIRC those engines came with steel-shim headgaskets at .020.
If you typed .057 correctly, then you have just created .037 more room, so taking off .015 means you still have an extra .022 That's a lot, and possibly nearly 5cc. That's a huge loss of compression in that engine. IMO, you need a new game-plan.
If the decks are serviceable,you could get the same results with headgaskets .015 thinner, or .042.. without spending all that money.
BUT
If the pistons are pop-ups, that is to say, if any part of the new piston comes above the deck... as it currently stands, then STOP, you need a new plan

 

[4spdragtop]

I googled that part # and got an eBay link to Falcon. The pistons don't look like commando pistons.
Any way to get a link or a good pic?

post up that Falcon Performance 273-4 kit link. I couldnt find it.

Thanks, I do not know how to post up a link, but I bought the rebuild kit number1847-300 through Falcon Performance. When I was looking for a rebuild HiPo kit for the 273, I typed that information in, and Falcon Performance came up. Thanks for your help. Much appreciated. Old Dart 66

 

[Deleted member 38666]

I googled that part # and got an eBay link to Falcon. The pistons don't look like commando pistons.
Any way to get a link or a good pic?

Thanks 4sp. As I said, I am not much of a mechanic, but the rep at Falcon and Rich at Packard told me that the kit was a HiPo rebuild kit. Currently, the pistons are at the machine shop as they needed them for boring the block for the 30 over plus clearance. I did take one of them out of the packaging, and they do have the two valve relief and the dome on the opposing side. Could it be that the Falcon, Packard, Katner, Egge pistons are built as a form of the original commando piston....therefore they do not look like commando pistons? I can post a photo of one of the pistons this coming week when I get the block back. The original pistons that were taken out of the original 273 block that is being decked and bored were the 4 valve relief. Thanks, I appreciate your input. Old Dart 66

 

[Deleted member 38666]

IIRC those engines came with steel-shim headgaskets at .020.
If you typed .057 correctly, then you have just created .037 more room, so taking off .015 means you still have an extra .022 That's a lot, and possibly nearly 5cc. That's a huge loss of compression in that engine. IMO, you need a new game-plan.
If the decks are serviceable,you could get the same results with headgaskets .015 thinner, or .042.. without spending all that money.
BUT
If the pistons are pop-ups, that is to say, if any part of the new piston comes above the deck... as it currently stands, then STOP, you need a new plan

Good to know. As I commented, i am no mechanic, and I will be assisting a mechanic when we get to the assembly part of this project. The block is already decked, so, the $$ is spent on that, an, when I called them this a.m. the cylinder boring has begun. Therefore, I guess I am putting my trust in the machine shop on what work they recommended and have done. At this point, I guess we will have to see how it goes together. The heads have, what appears to have a wedge shape which, I would guess, allows room for the piston half dome to enter along with the relief in the pistons on one side, for the valves. I did not take any photos of either the pistons, the head chamber, or the block. Maybe it would be best to post these photos when I get the parts back, and before I begin ANY assembly, then post my questions . Thank you for your advice. Old Dart 66

 

[AJ/FormS]

If the pistons come in above the deck,then
you are on the way to having a performance 273, if
or with, careful parts selection from this point on.

 

[Deleted member 38666]

If the pistons come in above the deck,then
you are on the way to having a performance 273, if
or with, careful parts selection from this point on.[/QUOTE

Thank you. From the beginning, the advice I recieved from the companies including Falcon Performance, Packard/Katner, Racer Brown Cams, and others was to do exactly that, to build a cloned OEM Commando 273 engine. I guess that was my objective by depending on these companies, my mechanic, and the machine shop which I am using which is well respected in my area. I got a bit concerned about the 0.015 block decking and, therefore, any clearance issues. However, based upon some of the answers I recieved the decking loss can be made up with the choice of the various head gasket thickness available. Although, there "could" be some intake fitment issues, but unlikely is what I have found. I am a paint and body guy with limited experience behind the wrench, so I thank you and all our members for the advice given. Old Dart 66