chev 186 double hump heads

[riverracer]

i'm trying to track down a plug fouling problem in a 350 chev with 186 double hump heads.

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all plugs are badly oil fouling. and i mean bad. drive 500km and they gunked up again.

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we have eliminated the intake gaskets and sucking oil in thru the valley, removed manifold twice to check.
valves, guides and positive seals replaced when heads recon'd.
even went as far as pulling engine apart in the car and replacing the rings.

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so here's a question,
do the rocker stud tapped holes protrude into the intake ports on these heads?
current thinking is if they do and they weren't sealed on the threads, that it could by sucking oil in thru them.
they have guide plates under them as well.
i could pull a couple, but i'd thought i'd ask first....

thanks

[Baprace]

Are you running aftermarket valve covers with a PC valve installed ? It's not the rocker studs.

[pdq67]

What's the heat range of your plugs?

A/C 44's or so??

Run your finger in the tops of your head ports and see if it comes out greasy as well as can you feel the stud holes?

pdq67

[user-612937456]

Are you running aftermarket valve covers with a PC valve installed ? It's not the rocker studs.

Been there before done that. Some of the aftermarket valve covers don't have a baffle underneath the PVC valve or the breather

[riverracer]

Are you running aftermarket valve covers with a PC valve installed ? It's not the rocker studs.

running stock chev pressed tin with baffle box under pcv locn. and plumbed as per assembly manual.

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What's the heat range of your plugs?
A/C 44's or so??

NGK BP4FS

Run your finger in the tops of your head ports and see if it comes out greasy as well as can you feel the stud holes?

heads are on the engine, in the car, still running, otherwise i would.

[Belgian1979]

Interesting. I'm going to follow this thread to see what comes up.
Have a similar problem but nowhere near as bad as how your plugs look. Engine puffs out a blue cloud when decelerating from high rpm and uses oil. I have been doing some work on the heads, replacing the valve guide seals. Didn't help. When doing that I could wiggle some of the valves indicating a valve guide problem. Compression test was ok.
However... this was not on all cyls and by judging from the plugs colour, the oil consumption is more general than those with a possible guide problem.
I'm still contemplating what to do. Was set on dropping the heads at the rebuilder to have the guides replaced, but that operation would set me back quite a bit and if that's not the root cause, it's a shame of the money.

Lately I was thinking that maybe the fact I use pistons with the piston pin up into the oil control ring had somethings to do with this.

[Carnut1]

Fuelies usually do not have studs go into the intake ports. If the heads have been ported they may have been opened to that point. Just because the heads were reconditioned doesn't mean the guides were done correctly. What type of guide? Was it broached or honed? Was the clearance set with a valve guide dial bore gauge? Are the Pushrods the right length to get the valve train geometry correct? Roller cam 350 can eat up guides in a hurry if all of these are not correct. If you are not sucking oil in from anywhere it is the guides. If you have coke deposits on the valve stem inside the port good chance it is the guides.

[mag2555]

There's a water jacket between the roof of the Intake runner on those heads, no ?

[riverracer]

Fuelies usually do not have studs go into the intake ports. If the heads have been ported they may have been opened to that point.

they were virgin heads and only had a gasket match and light bowl clean up.

have borrowed a bore scope, will remove the carb and stick it down thru manifold and see if i can see anything in ports or on valve stems.

will make a quick inline filter at work morrow and see if it's sucking oil from pcv into base of carb.
if it shows anything, might have to go catch can route.
wishing to avoid doing that as it's in a classic car, and don't want to detract from the stock look.

[tenxal]

Where is the vacuum source for the PCV valve located?

[fdicrasto]

So what makes you think the oiling source is in the heads?

[Belgian1979]

Fuelies usually do not have studs go into the intake ports. If the heads have been ported they may have been opened to that point. Just because the heads were reconditioned doesn't mean the guides were done correctly. What type of guide? Was it broached or honed? Was the clearance set with a valve guide dial bore gauge? Are the Pushrods the right length to get the valve train geometry correct? Roller cam 350 can eat up guides in a hurry if all of these are not correct. If you are not sucking oil in from anywhere it is the guides. If you have coke deposits on the valve stem inside the port good chance it is the guides.

Why is guide failure more prevalent on a roller 350 ?

[Carnut1]

Fuelies usually do not have studs go into the intake ports. If the heads have been ported they may have been opened to that point. Just because the heads were reconditioned doesn't mean the guides were done correctly. What type of guide? Was it broached or honed? Was the clearance set with a valve guide dial bore gauge? Are the Pushrods the right length to get the valve train geometry correct? Roller cam 350 can eat up guides in a hurry if all of these are not correct. If you are not sucking oil in from anywhere it is the guides. If you have coke deposits on the valve stem inside the port good chance it is the guides.

Why is guide failure more prevalent on a roller 350 ?


Rollers usually have higher lift and higher spring load which if geometry is not correct will eat up the guides on short order.

[ProPower engines]

Where is the PCV connected?? Also did you see a trail of oil through the intake?? Like is the ports through the intake oily?? Idf they are then thats a problem.
Bad valve guides even fresh guides depending on who did them can still be way too loose and suck oil even with new seals in a short time.

If the backs of the valves were oily or burnt black from too much oil getting in the guides thats another possible issue.
Most small shops install liners and I have seen cracked guides that have gone un noticed when they get replaced after a short time when the guides are machined for positive seals.

the other and most likely possibility is the ring seal is bad on the 2nd ring allowing too much oil in the chamber when running.
If the block was honed too rough the 1st time it will eat the rings in no time at all.

I would confirm the guides have no more then .0012" clearance and are straight as well as no run out or taper in the valve stems as this some times gets over looked and when a stem don't go in the guide some guys go up a broach size to get them to fit and alot of times crack the top of the guide.

Pull the intake or make a plate to cover the complete carb flange and vacuum test the intake ports and see if they suck oil past the seals. An easy way to test them all at the same time. Just be sure to remove all the rockers 1st.

You never mentioned how much vacuum it pulls while running. If it has good vacuum it may be a ring issue more then a guide issue with that much build up on the plugs in that short of time.

Where they new pistons??
It may be caused by badly worn ring grooves or the wrong ring width being used. A 1.5 mm and a 1/16 ring are just slightly different and will cause bad things to happen if thats the case or the 2nd ring installed backwards will make it suck oil.

[Dan Timberlake]

download/file.php?id=15424

Looks like a pretty big variation in gunki-ness.
Which cylinder had the tan insulator ( center, rear in that pic) , and which cylinder was gunked solid and wet ( front row, left) ?

I'd be REAL interested in the appearance of the intake runner of the wet one, as well as the valve stem clearance.

Just for the record, what ring manufacturer, and part number?
What were ring gaps? Got pictures of the cylinders during the re-ring job?

What make and model of valve stem seal?
How much retainer to seal clearance at full lift? Again, especially on the real bad cylinders.
The retainer to seal clearance can sometimes be checked just by pulling a valve cover, depending on the spring style.

For fun, here is how the Perfect Circle Corp described the performance of the teflon seal they had recently developed back in '59 .
PC tacked on a "discussion' after somebody else had submitted >> their << SAE paper.

Looks like I loaded them in reverse order. Sorry.

0.015" stem to guide clearance. Imagine that.