Just found this on Mondello's web site:

If you need to overbore and hone your engine, make sure the machinist has the pistons for your engine, before he starts his machine work. I know a lot of guys who call me and say I just had my block bored .030 over and I need a set of pistons. Odds are the pistons will probably be too tight in the cylinder bores, especially if they are forged T.R.W., Speed-Pro, Arias, etc.. I recommend .003 to .0035 on T.R.W. or Speed-Pro forged and .0045 to .005 on Arias forged Silicon pistons. On all cast pistons, even hypereutectic .002 to .0025 is recommended. We are allowing a little extra piston to wall clearance because of today’s unleaded gasoline.

 

I really hope its just something as simple as tuning to get the high idle down and out of the way, then fixing puttering out when off the trigger.
Hate to hear bad news like this after dropping 4K into an engine only to have to pull it out.
I hope this has a good outcome.

Eric

 

Yes, that's what the guys have been talking about. They're not kidding. It's a real thing.

It's good that you've gotten a number of small details squared away, but you still don't have the numbers for the bore size, so you still haven't gotten to the bottom of things.

- Eric

 

Unfortunately between this and a stuck valve slamming into a piston from inadequate center exhaust guide clearance, no wonder nobody runs Olds anymore. People think they are junk but actually need to be built different than a chebby.

 

This morning I found this thread talking about Speed-Pro clearance recommendations, no necessarily for Olds but still along the exact same line of thinking: to have the bores opened up a bit.

http://speedtalk.com/forum/viewtopic.php?f=1&t=41022

I'm not sure what clearance the machine shop aimed for or established, but if they followed the instructions with the pistons, then its likely too tight. If they followed what appears to be the general rule of thumb for forged, then it wouldn't be that. But what the hell else COULD it be at this point???

The only way that I'm going to know for sure is to pull the motor out.

 

... Or ask the machinist.

Also, you can pull a head and measure the bore without taking anything else apart
(if necessary, the machinist, who lives near you, could make the measurements accurately in five minutes in your garage).
The diameter of the pistons is stamped on their crowns.

- Eric

 

Is that the value that is used or is it necessary to actually measure the piston?

The way the motor is behaving is leading me to believe that this is the problem:

• It turns over easily enough and starts fine when cold. When it gets hot (and I'm only talking 220 degrees), the starter drags big time.
• When I try to idle it down as it warms up, it doesn't want to. It tries to die and I have to rev it a little to keep it from stalling. Its almost like it doesn't have the momentum or it's got a "brake" being applied that needs more power to overcome.
• When it does start to die, it diesels a little.

I don't think I'm going to risk causing any more harm to the pistons or cylinders by running it again. I'll pull the top end off and take a look in the bores for clues. I'll get the machinist to measure the bores in place, but I'm figuring it's all coming out.

 

Since these are new pistons made by a reputable company, their specified dimensions should be valid, but, of course, the ideal way is to take actual measurements.

It's a lot less trouble to pull a head, and if the bore sizes match what is specified in the piston's literature, instead of the correct, real-world numbers, you don't need to speculate much past that.

- Eric

 

So the thought is that the piston should have been manufactured to the exact diameter advertised, which is 4.087" (30 thousandths over stock). The actual bore diameter should be 4.087 plus 0.0025 (minimum) according to specs that I just pulled off of the Federal Mogul site. But what I'm hearing here and reading online is we're looking for 0.003 to 0.0035. That's only 1 thousandth of an inch difference. My guess is that we should find the reading to be LESS than 0.0025 if this is really the culprit.

 

I hesitate to contribute as you already seem to have many cooks in the kitchen, but since I have been dealing with this sort of situation for about 50 years and we are nearly neighbors I thought that I should. These engines seem to be sensitive to overheating when some things are not perfect, especially in our type of environment. When they do overheat it can be that the engine is generating too much heat, the radiator is insufficient to dissipate the heat, or both. As you have done a piston change, this is an area of concern. As others have noted the clearance may be too close. Your description of the running/idling/cranking characteristics point in that direction assuming that no coolant is entering a cylinder. When the cranking process becomes more difficult during "hot" times I suspect that the starter is not "dragging" as per your description, but rather that the engine is becoming more difficult to turn. Pursuit of the piston/bore clearance verification seems appropriate. Another consideration is the dissipation part. If the vehicle will be operated in a New Orleans environment, especially with A/C, install the largest capacity radiator which will fit. On mine, as I could never find an efficient fan clutch which would fit, I had to result to a flex fan and a custom shroud to maximize the cooling capacity of the radiator. Yours probably won't have that fan clutch constraint, but be sure that plenty air gets moved through the radiator during "hot" times. If you want a non-stock situation which may help, remove the thermostat and block the bypass. It warms up a bit slower, but that's rarely a problem in our environment. The cooler months ahead will also help, but remember that a globally warmed summer will follow, so do all you can to cool off that Oldsmobile. And after all is done, please let us know what helped and what didn't, as others will benefit. Best wishes!

 

I think you are underestimating the impact a .001" difference in clearance can have on the amount of friction generated by metal-on-metal parts.

 

No, they are manufactured to a size to give you their desired clearance. a .030" overbore of a 350 Olds is 4.087". The pistons manufacturer builds the clearance into the piston. So, the piston will probably measure around 4.0845" or thereabouts.

Also, I have never seen a piston with the size stamped onto the top of one.......and if the picture you posted earlier in the thread is your actual short block, they are not stamped into the top of your pistons. The only way to know is to pull one out.

I don't see why you couldn't ask your machinist what the piston to wall clearance is. I'm sure he would like to know this information if he indeed set it up per speed pro recommendations and made it too tight.

 

Not the size, per se, but the nominal size.

For instance, these should say "L2320F30" indicating 0.030"-over pistons.

Then it's a quick matter to look at the manufacturer's literature on line and see what the actual furnished size is.

- Eric

 

Not sure Speed Pro lists that......this is the most I could find

http://www.fme-cat.com/digipubZ/seal...age/#?page=992

 

Hmmmm... I'm a bit surprised that there is no listing of furnished size, but I agree - I can't find one either.

Here's a photo of the OP's piston crown, though, showing the markings:




- Eric

 

The whole concept of overboring is because at temps above where we're recommended to run (say 215-230) the skirts can flare on the pistons, making them outright snug in the bore. I went to .003" rather than .0025" on my bores, in hopes that I'm smart enough to shut it down before that bore size becomes a problem.
By the way, you can always bore an engine before you get pistons, then hone to size when they arrive. You can also hone another thou in no time if you want more clearance.

 

"Flare" isn't quite the right term, but your basic concept is correct. The piston is completely aluminum and has the same coefficient of thermal expansion from top to bottom. The piston crown will be hotter than the skirt and will actually expand more. The piston crown will be considerably hotter than the coolant temp.

The real problem is the different expansion rate of cast iron vs. aluminum. The cast iron cylinder expands at 5.8 μ in/in/deg F. That means that the bore on a 350 olds will grow 0.003" in diameter from room temp of 70 deg to a coolant temp of 210 deg.

The aluminum piston has a CTE of about 13 μ in/in/deg F, so it grows 0.007" in diameter over the same temp range. Forged pistons tend to expand more than cast.

You begin to see the problem if there is insufficient piston to wall clearance. This is an unstable system. As the coolant gets hotter, the pistons get even tighter, which makes the coolant get hotter, etc, etc. Scuffing ensues.

 

I've got another update:

I just spoke with my neighbor (Harvey) at his machine shop and explained everything to him. He didn't want to deny that it was the problem, but he also wasn't ready to jump into the deep end. The guy in the shop that did the work wasn't there to answer to what he remembered honing it to.

Harvey confirmed what 80Rocket said, which is that the bore diameter is the bore and the piston is manufactured to provide the clearance that the manufacturer feels is correct. He said that even if we pull the heads and measure the bored diameter, it's likely going to show us that it was taken to 4.087. Without being able to gauge the piston, he said we're still guessing at the clearance.

He also said that 1 thousandth could make the difference between quiet and noisy as the piston has that extra wiggle room.

I want to see the cylinders to put my mind at ease that they're not being harmed. I'm going to pull the heads and let him measure the bores. At the end of the day, I'm probably pulling the motor because I can't imagine what the hell else it could be.

And, BTW, I just picked up the brand-new copper/brass 3-row stock radiator from the distributor: $325 plus tax

Bill

 

Meant to toss out some props here to Joe for the 50-cent math! I'm an engineer and I can definitely appreciate your calcs!

Bill

 

Bill,
did you see any build up around the tubes before you filled it ? It usually plugs up on the drivers side tank more than the passenger. So if you seen any white or brown substance around the tubes when filling then you can be sure the other side of the core will be twice as bad. You could drain it down below the trans cooler and you will be able see that far down. That 3 row copper rad will definatly cool it if the engine isn't the issue.
Hope this helps
Eric

 

He sounds like a decent guy. If it turns out it is too tight it sounds like he will take care of it. I don't really want you to jump off the deep end either, but I have seen the exact same thing you are describing a few times already. I work at a performance machine shop so I get to see lots of interesting things.

Hope it works out!

 

Joe's analysis seems to make an analogy to a thermal runaway threshold in a semiconductor device where more heat equals better conduction which causes more heat, which causes .............failure of the device. If the numbers are correct for the components involved it would seem that the greater the difference in temperature between room temperature and operational temperature is, the greater the problem is. If the cylinder grows 0.003" and the piston grows 0.007" over the temperature range, it would seem that any clearance less than 0.004" at room temperature would lead to seizure before or at operational temperature. I always thought that some clearance (though perhaps small) was needed at operational temperature for lubrication purposes. Did I miss something?

 

Clearance in necessary. I have always setup 350 Oldsmobiles with .0045" clearance with the Speed Pro pistons.

 

There isn't a lot of mineral showing at the ends of the tubes, but it's not spotless either. I don't think its the radiator causing the problem. I had the water temp up to 220 degrees, it wasn't boiling over, but the "won't idle" problem and the inability to restart (starter strain) was there.

Also, even though the water temp is not catastrophic at that point, when it tries to die at low RPM, it diesels a little (at the low RPM) at as I rev it to wake it back up. Harvey said that sounds like high temps in the cylinder causing the fuel to detonate, which could be the piston overheating (it's not directly cooled).

Another thing I want to ask about is the valve guide clearance. Mondello claims that because of the exhaust crossover, the exhaust valves on the middle 4 cylinders get particularly hot, sometime causing valves to hang but not gall. If I'm tearing it down, I want to check that too. What does anyone know about that particular issue?

 

What are you typically finding out of the box? 0.0025 less than the 4.057 or 4.087 (30 over) bore? So you're boring/honing the block to perhaps 4.087 - 0.0025 + 0.0045? That would be a 30-over piston manufactured 0.0025 narrower than the published bore diameter and establishing 0.0045 clearance through machining on the block.

And at that clearance, does the piston start to make noise?

 

I think you might be making this a little more confusing than it actually is. Any machine shop that knows what they are doing will take a piston and measure it (the manufacturer sometimes will tell you on the literature where to take the measurement for their pistons). Once you have the measurement, you can then bore/hone the cylinder to reflect the desired piston to wall clearance.

I think you are taking the ".030 over" thing too literal. .030 over does not necessarily mean the bore HAS to be 4.087". .030 over is a general term.

Speed Pro pistons for small block Oldsmobiles are generally around 4.084"- 4.085". So, you measure the piston, and add .0045" to the piston size.....that will be your final bore size.

The piston does not make noise at .0045". I've seen one engine at .012" and it wasn't that loud (yes, twelve thousandths!, needless to say the skirts were collapsed). Although, it's kind of hard to hear it over open headers.

 

More progress, more questions, who knows what to make of the answers!

Harvey called after talking to the machinist. He said they measured the pistons and recalls about 0.003" established clearance.

He asked me to try the 3-row before pulling anything apart. I just did that this afternoon.

The good news is that this radiator REALLY cools! It took forever for it the motor to get to operating temps and when it did it stayed right at 180.

But the behavior is JUNK. The motor surges at idle and never really wants to go there to begin with. When it got to 180, it eventually died. Good news again - I was able to crank it up right away. But from stall or low idle into rev, it diesels. It doesn't accept any given idle setting. It stabilizes and eventually drifts to stall at one setting, then when I goose it a few times, the idle is racing.

Now I wish I had another spread bore to put on it to test. All I have is a square bore Holley on my Bel Air.

I've got a video that I took when I was doing all of this. I'm going to try to post it to YouTube or something to let you all have a listen.

 

Harvey just left. Based on what he's seeing and hearing, he's suggesting to cooling problem was fixed with the radiator and now we're dealing with a carburetor issue for the idle. The vacuum is low and the needle flutters slightly. Everything smooths out at higher RPMs. And of course, it won't idle. So, Eric 76olds, you may win the prize when we're done!

 

76 Olds guessed this one, your rad was obviously marginal before. But what I missed was the original, untouched Qjet from an 8 to 1 motor. I did the same, boosted compression from 8 to 9.5 to 1, ran shitty like you are describing. I would contact Ken at Everyday Performance. He did mine for around $300 two years ago. Complete recalibration without plating but included bushing work on the carb I sent him. I am betting the idle circuits need opening up, you need more fuel. Spray carb cleaner down the throat, if it smoothed out, there you go. After I got it back, it was the opposite, which is good since I mentioned stepping up to a bigger cam. Ran much better all around, very worthwhile. Your compression numbers sound great for regular fuel, which is good, eliminates one more potential issue.

 

It was completely reworked by Kinetic Performance months ago. It's like new. I was on the phone with him (Dayton) last night. I'm going to pull it off this morning and see what we find on the bench. He was suggesting the primary metering rod might be hanging open, causing it to riche the idle. There's umpteen other things that it could be, but this is the trail I'm hunting.

 

Any signs of a vacuum leak? It should be close then, were the throttle plates rebushed?

 

Ah yeah Put-r-ther!!! Dam I've never won anything. If I win what do I get haha?
Nah, but seriously,
The guys that have posted deserve all the credit including yourself for diving into this problem blind!!!
The trouble shooting posts are awesome for this site, even thou it may not be an engine issue.
Congrats to all that posted in this thread, Oldsmobiles rock here as do so many of the members.
Put-r-ther !!!
Cheers
Eric

 

MAJOR PROGRESS!

The cooling issue is solved with the new radiator. Now the tuning issue is DEFINITELY in the carb. I've had it on and off the car 3 times today. The boosters are dribbling. Talking with Dayton (carb rebuilder), we were working on a bypass in the throttle plates. It was definitely helping, but now the plate holes are as big as we're willing to go. I'm. ALLLLLMOST THERE.....

Any thoughtsuggestions on the Q-Jets having this problem? It's the original carb that was with this motor and it was in good shape to begin with. The only mod that he made was softening the power piston spring to account for lower vacuum with this cam, and my vacuum readings are right on the mark for what he planned.

Bill

 

[QUOTE=Racer24ksi;967795]MAJOR PROGRESS!

The cooling issue is solved with the new radiator.


That's great news Bill, Sounds like your well on your way getting your engine running good.
I must say,,,, MDchanic ( Eric ),,,, deserves a shout out for helping with your cooling question.
Post # 3 MDchanic suggests trying a new rad and see how it runs!! Eric always comes through with his awesome posts and experience.
Glad to hear your making good progress, I can't wait to hear how well it runs after you get everything dialed in.

Eric

 

Do you have Cliff Ruggles book? He shows where you need to open up the idle circuits.

 

With the softer power piston spring, if anything the plugs look a little rich, similar to mine. Those plugs, if anything should be a bit warm, heat range wise. My very cold NGK 5670-8 plugs turned a nice dark brown with some highway miles and 1/8 mile runs.

 

[QUOTE=76olds;967804]Thanks for the kind words, Eric!

I think we all try to call 'em like we see 'em.

- Eric

 

This may be too late to the party but once-upon-a-time I had an overheating issue after a refresh on a non-olds engine. New rings, bearings, cam and lifters. I couldn't get it to idle and it was overheating rapidly like yours was. It was running so hot the exhaust manifolds were glowing red. The carb was exactly as it was when taken off and it didn't have time to dry out or become fouled in any way. It would stumble and die before I could get under the hood to make any adjustments. The cam was not stock so I wasn't sure where the timing needed to be set. I finally had the Mrs. come out and start the engine and keep it running while I was under the hood to do some adjusting. It turns out the distributor timing was retarded so far it was causing the engine to run extremely hot. Once I was able to adjust the timing while the engine was running, things calmed down and I was able to complete the tune-up. So from what I have learned reading this site, Olds engines are accepting of a lot more timing advance than some others, you might try giving yours a little more and see what happens. Just a thought.

 

No, but I discovered his site today. The carb changes were helping, but I think we band-aided a partial solution that would have probably been better solved some other way. I think there may be something to opening up the idle tubes. Saw another post elsewhere about the booster nozzles being too far in the stream, making them more sensitive to air flow.

I also saw another site that said a LEAN fuel mixture can lead to a "rich" smelling exhaust. Basically a poor mixture leaves unburnt fuel in the exhaust. Mine is probably rich because it's essentially flooding.

I might not get to tinker with it for a few days, but I'm going to sleep easier knowing I don't have to pull the motor!

Thanks to all for the help and encouragement!

 

[QUOTE=MDchanic;967826]Your very welcome Eric, I came late to the thread posted and then read your post.
Nothing gets past you LOL, you know your Oldmobiles!!!
I'll have to forfeit the prize to you as always haha.
Its a good thing we all have you with us!!!!
Cheers
Eric H