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PostPosted: Sun Oct 21, 2018 8:43 pm 
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We just finished rebuilding the top end of my 356C and after an hour of running on a stand (to sort a few issues) then maybe 20 miles in the car driving it’s now blowing oil out of the vent to the point it’s running down the right carb and manifold (stock crankcase breather seatup and Zenith carbs). It’s also leaking from the crank pulley seal, right valve cover, possibly an oil return tube or 2 and case seam.

The top end was rebuilt with a Stoddard 1720cc AA Biral cylinder kit with JE forged aluminum pistons running 9.2:1 compression. The heads were checked and new valve guide seals were installed along with a complete top end seal kit. When driving on the road I didn’t exceed 3500 RPM.

Yesterday while driving, right after it basically warmed up, it began blowing ALOT of white smoke out of both tail pipes. I pulled off and shut down but saw no oil leaks or visible issues so I started it up and drove home with no more white smoke or issues. I assumed some oil was in the combustion chambers (leaked passed the unseated rings) and burned off as the engine reached operating temperature.

When I got home I noticed the oil running down the right carb and manifold and the oil leaks. It also seemed like there was a lot of pressure coming from the vent tube. It isn’t smoking at all now from the tailpipes.

Before we tear the engine down to check for a broken ring I wanted to see if anyone had any thoughts on potentially easier fixes or if they’d encountered similar problems with a setup like mine.

Thanks in advance for the help.

Greg


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PostPosted: Sun Oct 21, 2018 8:54 pm 
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Give the rings a chance to break in.

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PostPosted: Sun Oct 21, 2018 10:16 pm 
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In addition to allowing time for the rings to bed in you could monitor progress by doing a leak down test as the miles add up. That will at least tell you if the rings are indeed bedding in. I would also check the oil level. How much did you put in the engine initially? I always put in 4 quarts after a rebuild then check and see where it is on the dipstick. The dipstick tubes have been known to creep in both directions allowing for both under and over reading oil levels.

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PostPosted: Sun Oct 21, 2018 10:32 pm 
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Mr. Skirmants, I’ll keep driving it. I’ve never broken in a 356 engine and oil all over my engine compartment is a little disconcerting. I’ll vent the crankcase under the engine (Euro style) to prevent oil getting everywhere. Hopefully it stops venting so bad after more driving.

Mr. Jones, I added a Precision Matters full flow pump and the engine took about 5 quarts to get it between the lines. Overfilling had crossed my mind and maybe draining a little oil might help while trying to break in the engine and seat the rings.


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PostPosted: Mon Oct 22, 2018 8:14 am 
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I once tested a customer-built C engine. Test drove and thought it was a real dog. Had vented valve covers and oil was definitely coming out of the vents; quite a bit. Customer had me put un-vented covers on; as original. Test drove it again, and was amazed at the improvement in power with just that short of a break-in. Customer stated the power kept improving as the rings seated some more.

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PostPosted: Mon Oct 22, 2018 1:18 pm 
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If this continues past the 1000 mile mark you might want to go back in and have a look at the rings. I had a " rebuilt " engine with the same symptoms and after taking it down found that the rebuilder had installed the rings upside down.

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PostPosted: Mon Oct 22, 2018 7:22 pm 
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"It’s also leaking from the crank pulley seal, right valve cover, possibly an oil return tube or 2 and case seam." Boy Oh Boy! Those don't sound like they have anything to do with rings sealing.

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PostPosted: Tue Oct 23, 2018 11:23 am 
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Check in the right carb air cleaner where the crankcase vent tube is attached. There's a perforated screen in there. Make sure something isn't blocking it.

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PostPosted: Tue Oct 23, 2018 2:00 pm 
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Gents,

Thanks for the replies, I appreciate it.

To respond to some of your suggestions and questions:

- I believe the oil leaks out of the valve cover may be a warped valve cover and it's dripping off the head. I don't believe the push rod tube gaskets are leaking on second look.

- I sprayed solvent cleaner through the vent / mesh in the air cleaner and it apears to be clear and not blocking airflow

I swapped the breather hose to the air cleaner for a hose that goes down under the car (and plugged the vent hole in the air cleaner housing) to prevent oil gettng all over the right carb and manifiold. It's still venting oil / oil vapor under the car but at least it's not making a mess in the engine compartment as of now. I did notice the dipstick was also venting oil as well.

I'll keep driving it to see if things improve but right now I have about 30-40 miles on it.

Greg


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PostPosted: Tue Oct 23, 2018 2:38 pm 
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Greg, there is a procedure to seat rings. You want to roll the throttle on to wide open from a low to moderate rpm. It is best to do this in a higher gear like 3rd so that the acceleration is relatively slow and the period of high pressure in the cylinder is long. As the engine struggles to accelerate the very high pressure in the combustion chamber gets behind the rings and pushes them firmly against the cylinder. Modern cylinder and piston ring finishes usually seat very quickly but maybe this old school method will help.

Start the procedure around 2000-2500rpm and back off around 4000-4500rpm. Repeat this at least a few times. The object is to make the engine struggle but not to lug it.

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PostPosted: Tue Oct 23, 2018 10:36 pm 
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Greg,

There's a little 0-ring inside the dipstick's cap and w/years of age, it gets hard to remove for replacement.
You may need a dental pic to get it out.

Dick


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PostPosted: Wed Oct 24, 2018 9:43 am 
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Mr. Murray and Weiss, thanks for the comments / suggestions.

I reinstalled the Euro type vent system that was on the car when it had Webers so it's now breathing / venting under the car and not all over the right carb / manifold. I had been doing a process similar to that suggested by Mr. Murray since I started driving the car (per my mechanic buddy who helped me rebuild the top end) whenever I had the road available to do it. It appears, as of now, the oil venting is subsiding and I believe the rings have either begun to seat or have now seated (there's about 50 miles on the car as of this morning). I didn't notice any oil under the car in the vicinity of the vent tube outlet last night at shutdown or this morning and it doesn't look like the dipstick is venting any more (although I will look to change the o-ring now that I know its there). The car is not smoking and seems to have pretty good power so I'll drive it some more and then do a leak down and compression check to QA everything is working as it should.

I'll plan to put to some more miles on it (maybe 1000) then reinstall the correct coffee can filter and vent tube to the right carb once I'm sure it's done spraying oil. From there I may pull the engine and get the carb linkages sorted a little better along with a few other issues I see.

Mr. Weiss, are you still selling rebuilt crank pulleys?

Thanks again,
Greg


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PostPosted: Thu Oct 25, 2018 1:55 pm 
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An update,

I've been driving the car the last couple of days and have about 100 miles since the top end rebuild.

Today while driving on the interstate between my two work locations (first tme I've driven at interstate speed since rebuild) the engine started smoking heavily from the tail pipes again. Due to traffic, I wasn't able to pull off and check so I kept driving along at 60-65 MPH (RPM showed ~2800 altohugh I think my Tach may be off). After about 5 minutes the smoking subsided / went away until I put the pedal down harder (loaded the engine up more to accelerate) at which point it began smokng heavily again. After another minute or 2 it stopped smoking and had completely stopped smoking by the time I arrived at work. I revved the engine a bit in the parking lot at the engine bay and saw no smoke at all from the tail pipes. A check at the oil cap (with engine running) didn't really seem to indicate excessive case pressure but the bottom of the oil cap / inside of breather can was coverd in frothy oil vapor that looked like mayonaise. I think there's water in my oil from condensation and I haven't been able to drive long enough or get the oil hot enough to burn off the moisture.

At this point, the smoking heavily for several minutes as the engine gets warmed up or put under load at higher revs / speed has got me a bit stumped and concerned.

Any thoughts?


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PostPosted: Thu Oct 25, 2018 2:25 pm 
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Greg Carter wrote:
An update,

I've been driving the car the last couple of days and have about 100 miles since the top end rebuild.

Today while driving on the interstate between my two work locations (first tme I've driven at interstate speed since rebuild) the engine started smoking heavily from the tail pipes again. Due to traffic, I wasn't able to pull off and check so I kept driving along at 60-65 MPH (RPM showed ~2800 altohugh I think my Tach may be off). After about 5 minutes the smoking subsided / went away until I put the pedal down harder (loaded the engine up more to accelerate) at which point it began smokng heavily again. After another minute or 2 it stopped smoking and had completely stopped smoking by the time I arrived at work. I revved the engine a bit in the parking lot at the engine bay and saw no smoke at all from the tail pipes. A check at the oil cap (with engine running) didn't really seem to indicate excessive case pressure but the bottom of the oil cap / inside of breather can was coverd in frothy oil vapor that looked like mayonaise. I think there's water in my oil from condensation and I haven't been able to drive long enough or get the oil hot enough to burn off the moisture.

At this point, the smoking heavily for several minutes as the engine gets warmed up or put under load at higher revs / speed has got me a bit stumped and concerned.

Any thoughts?


I had this with my 912 after I did a top end. I was trying to see how cheap I could pull of a top end rebuild so used the old stock cyls and Pistons and simply honed and re ringed.
Smoked like a chimney at first and still continue doing to smoke for years. I simply added oil and contributed toward global warming until the thing blew cooler seals an now its torn down for a rebuild.
Sounds like your rings still have not seated to me.

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PostPosted: Thu Oct 25, 2018 8:40 pm 
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I think the obvious that you have a mechanical problem. I can assure you that by running and/or flogging the engine you will do nothing more than make it worse.!Believe it or not your engine cannot heal itself. I would check the end gap on the piston rings. Check the assembly of the rings on the pistons especially if you use 3 or 4 piece oil control rings. As you know valves wear out. Usually they are tapered at the bottom end of the stem and can pass oil through both the exhaust and intake guide. Once you hav4 the valves out of the head, borrow a no-go gauge and check the size of the guide. Each guide must be fitted to the head and usually needs to be sized on a lathe for proper fit. Finally you should have installed new valve springs. While you were there did you check your rod bearings, connecting rod big end size and the drive on the oil pump? al zim 2018/10/25

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