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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I just got a 1987 Camaro Z28 305 tpi auto that is almost all stock and will remain that way for the rest of the time I own it. The only thing it has is a cat back exhaust. Upon a close mechanical inspection I found worn/brittle valve seals and low compression in #5 cylinder.
I pulled the motor and had it checked at the machine shop. The bores are fine and just need a de-glazing from a bottle hone. The #5 piston had the tip broken off the skirt and the broken piece was in the bottom of the pan.
My plan is to re-ring, bearing, and gasket the engine. Since I have to buy a new piston and am finding it hard to get just 1 piston I have to buy a set of 8.
They offer them in dish w/4 valve reliefs and flat top w/4 valve reliefs. Dish pistons will keep the 9.3:1 compression ratio.
Since I'm buying new pistons would it be worth it/ok to use flat top pistons w/4 valve reliefs to raise the compression?
Normally I would run the numbers in a calculator to see compression but I don't know the specs on the stock vs flat top pistons yet. So far just throwing around ideas.
Most pistons you might ordinarily buy add .020" or so of deck clearance to the already excessive stock .025 - .035". They do this so that if the block has been decked, as might be the case with a blown head gasket and severe scouring of the deck, the pistons won't crash into the heads. Yeah I know; wasn't my idea; it's just How It's Done.
Look CAREFULLY at the ACTUAL "compression height" of whatever you buy; the distance from the center of the pin bore to the top surface of the piston. Stock nominal is 1.56" which will preserve the excessive factory deck clearance. 1.54" is more typical, and adds the extra .020" of "rebuilder" clearance. Piston mfrs are notoriously vague about this spec; you get the usual "designed to fit" weasel-wording; best thing to do is take a mic to them. A few mfrs (they cost more; surprise!!) make them correctly and are up-front about it.
Your LB9 should have flat-tops, unless somebody already swapped it out or something. Flat-tops give about 9¼:1 IRL, "specs" aside; dish give about 8½:1.
Most of the replacement pistons I am looking at are 1.54" compression height. So If the block doesn't get decked, will a 1.54" compression height create excessive deck clearance, "piston in the hole"?
Here is my piston I took out. All of them have the same design. It doesn't look like the motor had ever been out of the car judging by everything still bolted to the block.
Any idea how the piston skirt broke? Over rev, detonation?
Here is what is described as "Flat Top" on rockauto.
Not stock LB9 pistons. Not much more to say about that. Doesn't matter what is, or isn't, bolted to the block. You can check the stamping on the deck to see if it matches the car's VIN.
Head castings should be 081 if stock. 187 would be the typical TBI one. Rear main seal should be 1-pc.
Usual cause of skirt breakage like that is excessive RPMs. Quite some time ago, judging from the patina on the break.
That Sealed Power piston I do believe is one of the majority that include the extra .020" of deck clearance. Yes that will create lower compression than ideal, and poor "quench". The "ideal" engine of this type (SBC) for typical "hot street" use would use flat-tops (with 2 VRs usually), crank journals EXACTLY 1.74" from the crank centerline and EXACTLY 90° apart with the #1/2 rod pin EXACTLY in line with the Woodruff key slot, rods EXACTLY 5.700" long center-to-center, have the pistons level with the deck at TDC, and use a head gasket in the .035 - 040" range. Having 4 VRs lowers the compression a little but allows all 4 pistons on each side to be the same. Really CHEEEEEEP pistons have all 8 the same which is not ideal at all. "Ideal" pistons would have 2 each of 4 different configurations; front to the left or right (left or right bank), and exh toward the front or int toward the front. You most probably don't need to get that **** about it ($$$$) but some people might.
Crank grinding "on the wear" instead of "index grinding", and "reconditioning" rods which shortens them, are other common causes of large and variable deck clearance. Rebuilt motors often have deck clearance variation in excess of .015". To "zero deck" the block requires attention to those details, as well as, usually, decking the block; paying particular attention to making the decks EXACTLY parallel to the crank centerline in the front-rear direction and EXACTLY perpendicular in the int-exh direction, as well as assuring that the bores are EXACTLY perpendicular to the crank centerline and EXACTLY centered on the crank journals. None of those things are generally true of stock motors and are virtually universally ignored and further deviated by rebuilders. The payoff in overall performance is MASSIVE.
Where is the stamping? On the passenger side front tab of the deck? What part of the VIN should it match to?
Some searches here say that 87-up 305s had those dished pistons. The part # on the inside of the piston is 14093663.
Heads are 081. If the motor isn't original to the car now I am wondering if the cam is the right one? I will have to check.
I don't think the rods have every been reconditioned as they have bearings stamped GM 86 and 0.0005. My machine shop guy said back them GM assembly had a box of different bearings to choose from to make clearances fit better.
I want to put this motor back together in pure stock form with no performance upgrades.
What you do recommend for a stock replacement piston that will keep the proper deck clearance?
DO NOT hone the engine. Just install normal cast iron rings. Honing on a rebuild is to be avoided unless ABSOLUTELY necessary, and if you are buying pistons and the bore's are wrecked - bore it oversized and do a nice plateau hone finish (at about 500-600 grit).
And yes the block deck should be addressed - your deck looks like crap. I like all the pistons 0.025" in the hole with a 0.015" gasket for a 0.040" quench. Less gasket = stronger, and less area for combustion to attack the gasket. And it preserves deck height. You will need a new surface anyway for a MLS gasket to seal properly. The machine shop should be able to hit this number on every cylinder if they know what they are doing - by way of line hone on the crank, and reconditioning the rods in conjunction with a proper decking you can get all the pistons to the exact same height.
Machine everything EXCEPT the bore's if you can help it. Don't touch a good used cylinder bore.
The bores were all checked and came out good. Only the #1 cylinder was worn .0004". So it won't be overbored
The machine shop said it didn't need a hone but a deglazing with bottle brush. I don't know enough to say if a bottle brush deglazing is different than a hone.
The bores were all checked and came out good. Only the #1 cylinder was worn .0004". So it won't be overbored
The machine shop said it didn't need a hone but a deglazing with bottle brush. I don't know enough to say if a bottle brush deglazing is different than a hone.
There's no such thing as "glaze". Don't touch them with any crude bottle brush instrument. Just LEAVE THEM ALONE.
The line of numbers below the "VO..." is the last however many of the VIN of the vehicle the block came from.
AFAIK all 305s from 86 or 87 on up came with flat-tops. Even the LG4.
I have no idea about any specific 305 pistons. I've made the mistake of spending money on a 305 short block once already. Never again. I can think of very few better ways to spend too much and get too little.
The line of numbers below the "VO..." is the last however many of the VIN of the vehicle the block came from.
AFAIK all 305s from 86 or 87 on up came with flat-tops. Even the LG4.
I have no idea about any specific 305 pistons. I've made the mistake of spending money on a 305 short block once already. Never again. I can think of very few better ways to spend too much and get too little.
I cleaned the pad more and the numbers match the last 6 digits of the vin of the car. The mystery deepens. lol.
Normally I would throw the 305 out and put a 350 in, but I've had enough cars with maxed out engines over the years. I want this car to be as close to stock as the day it rolled off the assembly line.
I checked the cam lobe lift with a dial indicator on a lifter and got .234" & .257" which matches the 87 A/T 305 tpi cam.
Your machine shop should have a 55 gallon drum full of 305 std bore pistons waiting to be hauled to the scrapyard. Ask him if it's OK for you to dig through it. You will find a matching piston.
Your machine shop should have a 55 gallon drum full of 305 std bore pistons waiting to be hauled to the scrapyard. Ask him if it's OK for you to dig through it. You will find a matching piston.
That was the first question I asked. Surprisingly they didn't and neither did the other machine shop across town.
That was the first question I asked. Surprisingly they didn't and neither did the other machine shop across town.
Someone on this site must have one, or know of someone that does. Post an ad in the Classifieds - Parts Wanted.
I can check the shop down the street from me, if you wish. 87 305 std bore 4 eyebrow, correct?
Like this?
Someone on this site must have one, or know of someone that does. Post an ad in the Classifieds - Parts Wanted.
I can check the shop down the street from me, if you wish. 87 305 std bore 4 eyebrow, correct?
Like this?
I appreciate that, but I'm sure by the time it was shipped to me in Canada it wouldn't be cheap.
My 100% stock 1992 305 block right before the rebuild. Has the same pistons as in the pictures above, and the new pistons are the same as the old ones, just .030 over.
My 100% stock 1992 305 block right before the rebuild. Has the same pistons as in the pictures above, and the new pistons are the same as the old ones, just .030 over.
Do you know what pistons and the part # did you used? Did you worry about the compression/deck height?
I believe this picture is going to prove what Sofa posted about the reduced compression heights of some replacement pistons.
This picture shows that this block was not decked, and it looks to me that these pistons do in fact have the reduced compression height of an additional .020".
Therefore the top of these pistons at TDC is already beyond the ideal .040" quench and is actually at about .045" right now. Add the thinnest head gasket of .015" to that and you now have a quench of .060". Not the best for performance and anti-knock resistance.
I looked them up. I was correct - 1.540"
Whatever you do to complete this build, DO NOT use a thick head gasket such as the FelPro FS 7733 PT2 (.039") or FelPro 1003 (.041"). You will end up with a quench of about .085". And using a head with a smaller combustion chamber will not correct for the poor quench and lost compression.
Last edited by NoEmissions84TA; 08-17-2020 at 05:45 PM.
This whole post is a litany of why I warn people against "cheeeeeeeeep" rebuilds. Why somebody can spend giga$$$$ on some mountain motor parts list, only to have somebody in the other lane or acoupla rows back, with a quarter as much "invested" under the hood and only in some ordinary off-the-shelf nothing stuff, WAX THEIR PRIVATES in public. It's because they PAID ATTENTION to what matters. Straight, parallel, perpendicular, consistent, centered, measured, known, ... big $$$$ stuff can be JUST as fornicated as cheeeeeeeep stuff, if you don't PAY ATTENTION.
Attention to this kind of details is what separates the winners from the whiners. It's why, when I was building motors alot, mine would not necessarily "win" every time, but they SURE AS HELL wouldn't LOSE for a blown motor anywhere near as much; and why my competition would build motors that would run maybe 8 events (including qualifying, heat races, buybacks, last chances, consolations, mains, finals) where mine would go 12 to 15. My customers didn't LOSE races near as much because their motors laid down on them. You can't always, or even often, WIN a race with your motor, but you can SURE AS HELL lose em. Any motor can fail; and like hard drives, there's only 2 kinds, those that HAVE crashed, and those that WILL; but if you can go longer BETWEEN failures, your odds are VASTLY improved. Not to mention, the ultimate thickness of your wallet.
Details matter. Spend your money where it makes a difference. And that's not, buying what "all the fast cars" have; it's what makes YOUR combo AS NEAR PERFECT as you can get it.
And though I know it's not what you want to hear, the single biggest improvement you can make to the motor you've got, is a "bore kit". Part # will end in 683 or 880. Don't be a Trump and fire all the people who tell you THE TRUTH and hire ones that tell you what you want to hear.
Last edited by sofakingdom; 08-17-2020 at 07:41 PM.
This whole post is a litany of why I warn people against "cheeeeeeeeep" rebuilds. Why somebody can spend giga$$$$ on some mountain motor parts list, only to have somebody in the other lane or acoupla rows back, with a quarter as much "invested" under the hood and only in some ordinary off-the-shelf nothing stuff, WAX THEIR PRIVATES in public. It's because they PAID ATTENTION to what matters. Straight, parallel, perpendicular, consistent, centered, measured, known, ... big $$$$ stuff can be JUST as fornicated as cheeeeeeeep stuff, if you don't PAY ATTENTION.
Attention to this kind of details is what separates the winners from the whiners. It's why, when I was building motors alot, mine would not necessarily "win" every time, but they SURE AS HELL wouldn't LOSE for a blown motor anywhere near as much; and why my competition would build motors that would run maybe 8 events (including qualifying, heat races, buybacks, last chances, consolations, mains, finals) where mine would go 12 to 15. My customers didn't LOSE races near as much because their motors laid down on them. You can't always, or even often, WIN a race with your motor, but you can SURE AS HELL lose em. Any motor can fail; and like hard drives, there's only 2 kinds, those that HAVE crashed, and those that WILL; but if you can go longer BETWEEN failures, your odds are VASTLY improved. Not to mention, the ultimate thickness of your wallet.
Details matter. Spend your money where it makes a difference. And that's not, buying what "all the fast cars" have; it's what makes YOUR combo AS NEAR PERFECT as you can get it.
And though I know it's not what you want to hear, the single biggest improvement you can make to the motor you've got, is a "bore kit". Part # will end in 683 or 880. Don't be a Trump and fire all the people who tell you THE TRUTH and hire ones that tell you what you want to hear.
Believe it or not, I am looking for zero improvement in performance. Simply to put the motor back in running condition from 1987. And if that involves decking the block and selecting a piston to give .040" quench height, then that's what will happen.
That's OK. Totally OK to say that, going into the project.
OTOH, I can hardly wait to see what will happen once it's all said and done. At which time, most likely, as is always the case, ALOT more will have been said, than done.
Few people who own "sporty" cars can tolerate getting drilled at stop lights by soccer moms in minivans. But that's EXACTLY where a 305 "back in running condition from 1987" will put you, by the time you're finished, in 2021 or 2022 or whenever. A Kia Soul, or a Toyota Yaris, or a Frod Focus (if any are still left moving), will humiliate you.
You are at a fork in the road. As a very wise man once said, "when you come to a fork in the road, take it". You will spend $xxxx on "fixing" this 305 and "restoring" it to "like new" condition. Not a bad thing, in and of itself, don't get me wrong. After which, you will get drilled at stop lights by soccer moms in minivans. At which time, your next thought will be, damn, for another $50, the cost of that "bore kit", less than 2% of the total cost of my "restoration", I coulda had 15% MINIMUM more whooma-whooma. Don't worry, you can protest all you want NOW, just like you are doing, but come a year or 2 down the road, and acoupla minivans, ... things will look different. Happens to everybody. One of the hallmarks of being young is the whole "it can't happen to me, I'm different" mindset. Problem is, once it happens, you realize you're really not so different after all. No matter how it looks to you now.
Get yourself a "bore kit", part # 638 or 880, and spend your money on THAT instead. Imagine you're going to the grocery store and you've got $10 to spend. You could buy bologna for $10 a pound, chicken for $10 a pound, round steak for $10 a pound, T-bone for $10 a pound, or filet mignon for $10 a pound. (I like em all, for the record) HONESTLY... would you walk outta that store $10 poorer with a pound of bologna???? That's RIGHT WHERE YOU ARE right now. YOU get to decide: you're gonna spend $xxxx dollars "rebuilding" a motor; what motor will it be? Doesn't matter what motor you "rebuild"; it's gonna be THE SAME $xxxx. DON'T make the mistake of it being a 305. Bologna is what you will get instead of T-bone.
08-15-2020, 09:52 AM
It's why, when I was building motors alot, mine would not necessarily "win" every time, but they SURE AS HELL wouldn't LOSE for a blown motor anywhere near as much; and why my competition would build motors that would run maybe 8 events (including qualifying, heat races, buybacks, last chances, consolations, mains, finals) where mine would go 12 to 15. My customers didn't LOSE races near as much because their motors laid down on them. You can't always, or even often, WIN a race with your motor, but you can SURE AS HELL lose em. 
Don't be a Trump and fire all the people who tell you THE TRUTH and hire ones that tell you what you want to hear. 