Westlotorn

They may install new cam bearings properly and totally fix your block. While it is at the shop you might ask them to dial bore gauge your cylinders so you have some idea what piston clearance you have and if the bores are straight and true to blueprint.

Good Luck.

Mark

lars

I just did a "cc" check on the heads I'm using, and my "64cc" heads are actually only 60cc. This changes things for me dramatically. So it's very important to actually verify the cc volume and not "assume" anything.

If your heads really are 64 cc, and if you use those Sealed Power pistons with the 4 valve reliefs (those add up to about 5cc's of dish volume) with the .033" deck height in the .030+ block, a .015" gasket will give you actual compression ratio of 9.59:1. Not a bad number.
Lars

boat196

Lars
When you cc a set of cylinder heads do you check each chamber. And also what is an acceptable tolerance between the smallest chamber and the largest chamber.
Bob

lars

My experience with the "as cast" Chevy combustion chambers is that they will be within about 1/2cc of each other, therefore checking all of them has little value. I have seen a 1cc variation on heads with bad valve jobs caused by valves that were inconsistently recessed into the heads. On heads such as the Pontiacs, the chambers are all fully machined, and they're all exactly the same on any given head. I checked 2 of the chambers in each of the 2 heads I'm working with now, and all 4 were the same within the measurement capability of my syringe with 1cc graduations.
Lars

cardo0

Awe, a little deviation just spreads out the power band.

Myself using my graduated cylinder (and iso alcohol) to measure I can't get any more accurate than 1cc. Sometimes I call it 1/2cc but I think there are so many possible errors 1/2cc is wishful thinking. I also have 1cc eye drop applicators but that doesn't seem to help much at all. I guess the 1cc helps when measuring piston eyebrows but not much else.

lars

This is 100% correct and a darned good point to keep in mind. The Sealed Power 310P cast pistons, that everybody uses because they are readily available and "affordable," have a compression height of 1.654". That's why your pistons are .033" down in the bore at TDC. "Good" pistons are at the "correct" compression height, which is 1.675 on a 327. If you replace the "cheap" pistons with some nicely-made forged performance pistons, your deck height is going to be about .012", and this will factor into your compression ratio calculation.

Lars

SledgeHammer 2.0

Thanks Lars...
Well I dropped my disassembled short block off at the machine shop. After the discussion, they set a straight edge across the cam journals and it is warped (?). Guess that's the word for it. They are going to check the line bore of the cam journals but feel the bearings are bad due to the cam. I ordered a CC kit from Jegs so I can CC my own heads. Then I can decide if I can run those pistons or get another set. I decided that I am trying to run the 292 heads....

cardo0

Hmm, can that shop correct those cam journals? I'm curious how they do it. An update if and when possible on that would be greatly appreciated.

Robert61

You couldn't check them that way. 3&4 are one size, 2&5 are another size, and 1 is yet a different size so a straight edge is going to do nothing. The best way to check them is with new bearings, if the cam turns freely after they are they are installed it's good. They could measure the diameter but if it's wrong they should feel it when they drive the new bearings in.

lars

Highly unlikely, and you can't check them, like that, as Robert correctly notes... The entire block would have to be completely warped in order for that to happen. Again... not likely...

Lars

Robert61

I just did these yesterday for a friend I'm building a 327 for. These come from a very poor late 60s rebuild. The car has been sitting since the early 70s. They knurled the Pistons and when they did the valve job they only cut the 45* angle which was common back in the day. The reason Lars might say my valve job is bad is I only ground enough for the seats to come in. If some happen to be lower than others that's where I stopped. This is where you get variation in chamber volume. I can't see the need to cut good material away just to say I evened out the depths. These could vary as much as 3 CCs which in my opinion will not affect any thing. The guy paid nothing for me installing the guides or doing the valve job so he can't complain too much. As you can see in the pics the intake seat is about 5/16" wide which is very bad. Then you can see the 3 angles where I ground the fresh seat. I grind them with a stone whereas most shops today use machines that cut all three angles at once. I'll put the concentricity of the stone ground against any machine cut, meaning the seat is true and perpendicular to the guide.

SledgeHammer 2.0

Oh Great, that's leads me to an all new confidence in the machine shop.

The machinist says he can check the cam bore for straightness, like they do for crank bores. (line bore) Don't know how they would fix it if it was off and Honestly I see no way the line bore of a cam could be off on a 60 year old block.The original engine would have failed decades ago and some one by now would have hopefully thrown the block away.
I think either the cam was (is) messed up (maybe) or someone just butchered up the cam bearings on the last install (more than likely)

SledgeHammer 2.0

Well, My 64 CC heads measured 65 CC's, checked 4 of them. I used water with my CC syringe, and had a spark plug in the hole. That calculates out to 9.47 according to the online calculator.

If I get pistons with the correct 1.675 Compression height and a -.050CC dome I can run a regular .041 thickness head gasket and have 9.79 compression. Is that .32 more compression worth $400.00 of pistons? Keith Black KB157-030 is the pistons I was looking at. But they say the compression ratio would be 10.5 with a 64 CC head. The calculators I use say 9.79

Robert61

As your engine is currently configured you have approximately 9.2. By changing the pistons to forged 4 valve relief it would go to approximately 9.7. This is with a .019" gasket. With no other changes in my experience the most you could expect to gain would be 20 hp at wide open throttle, considerably less in the lower rpm range. Is it worth it, that's entirely up to you.


670 CCs swept vol
65 CC chamb
6 Valve relief
7 Deck volume .033 deck
4 Head gasket



Just so you know you don't check the main bearing bore for straightness with a straight edge either.

cardo0

Well for iron heads you should consider c.r. <9.5 unless you plan you use a large duration camshaft. And for a stock rebuild making <1hp/c.i. a stock cast piston is okay unless you plan to rev it to death. I like silv-o-lite #1423 as they are flat tops with only 4cc eyebrows (dish). Compressed height is only 1.654" though so you need to decide on that. But for only $183 or less they can be bought from the shelf up to 0.080" overbore.

Good luck.

cardo0

So using your 0.033" measurement of the speed pro 310P piston recess/clearance in post #1 I come up with the calculation your deck has been milled 0.013" from stock 9.025" deck height.

The normal replacement piston compressed height seems to be 1.654" from what I can find. That leaves you with a quench height of 0.048" only if you use a 0.015" head gasket (steel shim). What I'm saying if you are concerned and want to have a good quench height you will have to mill the block deck more. Just something to consider before making accurate c.r. calculations.

This is a good time to run several c.r. calculations for the combinations you plan to use to see what you would be interested using. And the more you do it the more accurate you become.

Take your time and make it fun instead of a headache is my advice.

SledgeHammer 2.0

I think the stock piston height is 1.675 and the stock piston is down .025. with a 1.654 Replacement piston and .033 down in the hole, It appears that it has been decked .013 as you stated.

With the pistons I have now the quench with a .015 head gasket should be .048 with a compression ratio of 9.47
If I switched to the pistons I was looking at with a .041 Head gasket the quench should be (.012+.041) .056 with a CR of the 9.79.

Maybe sticking with what I have is better than the other pistons. If I can get my quench down to .033 with a CR around 9.5, I am assuming that would be best... Using the stock replacement 350hp cam.

Westlotorn

Not to confuse you more but to add more facts. Your enigne is old, the connecting rods may have been machined, re sized more than once also which takes a little more off the stroke.

As far as cam bores, the factory machine that bored the bores in the casting was not that accurate. The factory purchased un fininshed cam bearings and the material was a soft lead/Tin blend that allowed a lot of flexibility.

The unfinished cam bearings were installed in the block at the factory. A brosch was used to bore the cam bearings to size and then the cam was installed. Again, in a lead / tin bearing material you have a very flexible material.

At the rebuilders that are trying to properly rebuild these old engines they don't have the unfinished cam bearings to install and they don't have the factory tools to brosch the bearings.

Most common they use a Cam Spoon to fix problems. They install the camshaft, if it goes in good and spins free all is good, if not the find the tight spots and start carving on the new bearings.

A better method I have seen used at some shops is a modified camshaft that is used to make sure the cam bore is ready for use. A old camshaft is modified, a slot is cut accross each cam bearing journal on the donor camshaft.

These slots are cut at an angle so when you turn the cam on install they can cut any material necessary out of the way and make your cam bearings true for a new camshaft.

It is not perfect but necessary to get clearance sometimes. The Tin/Lead bearings will flow a little when run and form a surface that works. On occation a block is bad and the alignment is not good in the cam journals.

In these blocks sometimes they have to carve so much material out that the opposite side ends up with a loose spot. This loose spot is now an internal oil leak and will cost you some oil pressure.

A high volume oil pump will correct this low pressure issue and the engine will go on to live a full life. Back in the 90's I did know of a shop that was boring the cam journals and installing Roller Bearings, this was not because the typical

cam bearings did not work it was because they wanted to run .700 lift and big valve spring pressures and the factory lead tin bearing did not hold up.

In many cases going to a roller camshaft added enough pressure on the cam bearings causing short life on the factory lead / tin bearings.

The factory started using aluminum cam bearings in the late 90's to increase cam bearing life with roller camshafts. I don't know what they did about the bore issues when they went aluminum bearings because you can't carve on the aluminum bearings.




You have to mock up each piston/Rod in each hole to determine proper deck height. The block may be perfectly square or it may have variance front to back or side to side.

For a stock passenger car rebuild very little of this matters, the enigne will run and the customer will be happy.

For a Corvette and with you wishing for the best it is always nice to try and get back close to factory blueprint if reasonable.




Small amounts of quench help resist detonation, polishing your chambers in the heads and your valve faces also help resist detonation allowing you to run more compression with more timing.





The 310P piston advertises a compression distance of 1.654 as already stated. The 310P does not advertise its volume but the Sealed Power Forged Piston with 4 valve reliefs part # L2165F is similar advertises a -5.4 cc volume for the Piston head.

It also lists the compression distance on this forged piston as 1.671, interesting the domed version of this piston L2166F with a .125 dome ( L79 Piston ) lists a compression distance of 1.674.

The L2165F flat top 4 valve relief piston might have slightly larger valve pockets for a little more camshaft than the 310P. Many of the original Sealed Power piston molds were modified in the 90's to allow use of the new heads with 2.05 intake valves and a little more lift than the stock cast 310P. I know they did many of the 350 pistons, not sure about the 327 pistons.

If you wish to have exact blueprint for your 310P piston call the Sealed Power Tech Line at 1-800-325-8886 or 1-800-334-3210, it may take 15 minutes on the phone but the techs can look up a blueprint and answer questions.

Some of these techs are very good gear heads and enjoy helping the customer.

Robert61

I recently helped a guy rebuilding a 312 y block for a 55 tbird. He had installed 3 sets of cam bearings all tight. He said he had tried everything to open up the bearings and boy had he. Someone told him to get ahold of me, he wanted to know if I could line bore them in place. I do have a portable line boring tool but I didn't want to use it for this, it's not an easy set up to bore all five and not move the bar. I told him when I ran into a block where I knew the bearings were going to be tight I used a pot chuck in a lathe and bored them before I installed them. I asked if he had the old cam but he said he wanted to save it. I left thinking he was going to bore the bearings. He installed a fourth set and calls me back. He let me use the old cam. I cut notches in it and line reamed the bearings in the block. I've reamed many sets over the years with one or two tight bearings but never a block with all five this tight. Anyway we reamed them and he was good to go except the almost $400 he spent on bearings.

SledgeHammer 2.0

So going on a month with my block sitting at the machine shop and they still haven't touched it. Every time I call they are "getting right on it". At what time do I pull it out and try somewhere else? Or is this like body shop jail, except for engines?