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  #1  
Old 08-22-2007, 02:28 PM
peeeot peeeot is offline
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Default Blow by.

Long time, no post! I haven't been messing with the old bird much over the past several months.

Even with a pcv valve, my engine is producing enough blow-by that at idle when everything's warmed up I will see gases coming out of the hood scoop. Compression is around 150 psi or so. I've been doing some reading on engine break-in and suspect that my engine saw too much low-speed, low-load operation since the installation of new rings, resulting in improper ring seating. Maybe the cylinder walls are glazed, I dunno. Does anyone have suggestions for how I might go about remedying this issue? Any hope for a proper ring break-in? What about products like engine restore?

Aside from the blow-by, the engine's performance is quite satisfactory.
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  #2  
Old 08-22-2007, 02:49 PM
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You might want to install Positive Crankcase Ventilation,it is very simple on this web site go to techincal page and you can see how to do it,I dont know if Alexander sells the adapter to do this if not John Dexter at the thunerbird ranch does sell the needed parts
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Old 08-23-2007, 11:16 AM
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Three questions:

* how many miles on your motor since you rebuilt it?
* what type of rings? (cast iron or chrome moly)
* what weight and type of oil?

You could squirt some oil in the cylinders and retry the compression test - this would tell you if it was the rings or not.

john
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Old 08-23-2007, 05:56 PM
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Not many miles. Less than 1000, I'd say offhand. But since the car wasn't legal and there were transmission issues when I first rebuilt it, most of the running it did early on was idling and low-speed (less than 40 mph) trolling around the neighborhood. The rings were cast iron, if I'm not mistaken. Oil is 10w30. I tried the oil squirt months ago and compression immediately jumped to 180 where I tested it. What I'm wondering is, did I somehow put in the wrong rings, have they failed to seat, and is there anything I can do about the present situation short of taking the engine apart again?
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Old 08-23-2007, 06:06 PM
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I have been travelling at low speeds in my neighborhood for four years on a rebuilt 352 engine in my 1960 Golde Top. I have never had it at highway speeds. I rarely drive it at more than 20 mph. It had no blow by ever. I used regular engine oil initially and changed to synthetic after the first oil change. The only difference over the years that I have noticed its that the engine runs smoother.

There is something wrong with your rebuild with either your compression or your oil rings. You should not get the blow by you describe no matter how you break in your engine.
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  #6  
Old 08-23-2007, 09:42 PM
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major question: did you use new pistons???

If so, ignore the rest. If not then you have the possibility that the grooves in the pistons are worn vertically and gas and oil are going around the ring. The clearance between the ring and the groove is only on the order of .002" or so in a new motor.

I also forgot to ask if the oil was synthetic - I will assume not. Synthetic would not be conducive to seating rings.

Do you know what grit the hone was done to??

I rebuilt my motor a couple of winters ago. The blow by ceased in about 40-50 miles even though the compression rings were chome moly and certainly not worn in that quickly.

Assuming the honing was decent and the pistons new, engine people tell me you need to get the motor up to temp and put some stress on it such as at highway speed. Steve Christ's book has some guidelines for engine break-in as well which I could scan in and email to you.

Frustrating!!!!

john
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Old 08-23-2007, 10:09 PM
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Agree-the rings are your problem,they do need some varied RPM for break-in. Watch what oil you use. That is too much blow-by for too long. Nail it a couple of times and let it come down from speed by itself, but don't run at a continuous speed for long periods. If they don't seat-in you have no choice but to tear it down, bummer!!
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  #8  
Old 08-24-2007, 01:44 AM
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I should make a clarification. I only see the blowby coming out of the hood scoop after I've been driving at sustained speeds for a while and then come to a traffic light or stop sign or something. If the car is just idling in the driveway, the pcv valve seems to be able to handle that amount of blowby just fine.

I did some varied highway dirving today, getting more aggressive with the throttle than I normally do then letting the car coast back down to below the speed limit. It handled it fine. I haven't driven enough since to tell whether that affected anything.

The pistons were not replaced. Someone had been through that engine before me; it showed evidence inside of previous machine work with little wear. I honed the cylinders with a standard three-prong hone like you get at the parts store.

I retained the box from the rings I installed. As far as I can tell based on the part number, they are standard size rings. What I can't recall is whether I made certain to measure cylinder diameter. It seems possible that I could have installed standard rings in cylinders bored .030 over, but that would be more careless than I give myself credit for... I didn't have any work done on the block except to install cam bearings but I know the crank was machined down such that I had to use .010 oversize main and rod bearings.
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Old 08-24-2007, 07:33 AM
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the fumes out of the hood scooop are probably coming from the oil filler cap, which does breathe. If you look at the underside of the hood in that area you may find film from fumes.

I guess the key question from me would be: did you use a feeler gauge and measure the vertical clearance between the rings and the piston groove??

Do you still have the old rings you took out???
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Old 08-24-2007, 01:33 PM
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If you have oil fumes coming out of the oil breather cap at idle, the screen at the back of the manifold may be clogged with oil and dirt. I don't know if you cleaned it out when you did the rebuild. It is rectangular, but you can get it outwith forceps through the blow by pipe hole with engine still in the car.
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