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Oil Fouled Spark Plugs On Only Rear 4 CylindersSBC


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Alright so here goes...I also posted on ChevyTalk to see what I can come up with. Sorry it's going to be long, but I'm throwing out all the information that I think is related that will just be asked of me anyway. I'll try to split it up.

 

My 383 is now three years old I built. It has less than 10,000 miles on it. (Not sure exactly because speedometer is a wee bit off) I put in all new internals including SRP Forged Pistons, PBM File fit my own rings The only thing that really isn't new is the Edelbrock Performer RPM intake that I bought used from a friend for dirt cheap. I'm running a Moroso 7 quart oil pan with built in windage tray and scraper with only a M-55 non-high volume oil pump and a really expensive (ouch) Milodon dipstick. My Monte has power brakes with an AC Delco master cylinder that's about 1 1/2 years old. I did most of my own head work including a three-angle valve job at school, port matching, (pockets were already ported) cut my valve spring seats for larger springs, and set my own valve spring height. The heads had new bronze valve guides installed by a very reputable machine shop, who also did all the machine work to my block (bore, splayed caps, line-bored, decked, freeze plugs, cam bearings, balancing, etc) The valve seals I'm using are ones he recommended because he said the posi-lock ones that I bought will actually keep my valves too dry.

 

The problem I'm having is that when I pulled my plugs for the first time after maybe 1000 (maybe more, maybe less) miles, only the rear four plugs were severely oil fouled! (Cylinders 5, 6, 7 and 8) I'm talking crusted on with solid oil or whatever it was so the gap of the plug was next to nothing! I showed my teacher and he suggested my vacuum modulator since the vacuum for it comes from the rear of the intake. Sure enough, I checked my trans level when it was hot and it was pretty overfilled which I thought would cause the modulator to suck up trans fluid and burn it. So I drained what I could from the hole of the vacuum modulator and the trans fluid level is where it should be now. I even bought a new B&M modulator just to make sure my old one wasn't bad. I changed the plugs and along I went.

I was also having some oil pan leaking issues at the time so I thought that was a cause for some oil loss. After I took care of the oil pan leaking, I still noticed the rear four spark plugs were getting fouled, but not as bad, and it was still using some oil...and still is to this day. I figured the spark plugs were getting fouled still because of maybe some residual trans fluid in lines...I don't know! I probably add about 1/2 quart every couple hundred miles. Which is a shame because I'm running 10w-40 AMSOIL! And we all know that's not cheap.

The spark plug fouling is much better, still barely a little evidence of oil contamination. Still using oil though. When I was home for spring break I put a vacuum gauge on it and it has about 15'' at idle and doesn't flutter around like any mechanical issue. I would think vacuum is a good sign of cylinder seal. I know, I should have checked compression too, and leak down, but I didn't have the time and now I'm back up here at school and won't be able to check it again until May.

 

What I was wondering was has anybody seen a cracked intake or intake gasket issue where it could suck up oil? If so, would the vacuum tell me this or would the oil be a thick liquid seal? I port-matched my heads and might of made the gap between ports a little thin, is there any possibility of ingesting oil there?

383Assy020-1.jpg

Now that I went through Airflow class, I think about the way a dual plane intake is setup...One half goes to cylinders 1,4,7, and 6 and the other half goes to cylinders 2,3,5, and 8. If you don't believe it, this may help:

PerformerRPM-1.jpg

Therefore how could the manifold suck up trans fluid or brake fluid (a leaky rear seal in the master cylinder into the power booster) and only foul spark plugs 5, 6, 7, and 8??? I don't think that would be an issue...

I also installed this fancy dipstick from Milodon when I built my engine: http://store.summitracing.com/partdetail.asp?autof...

and it never came with any type of oil level indicator mark! It's been so long that I don't remember how I marked it exactly if I just put it back to back with the original dipstick and marked it (which doesn't quite ring a bell because chances are they aren't the exact same lengths) But then again I don't think I removed the old dipstick and put the new one in while there was oil in the pan and marked where it was from looking at the one I pulled out because I'm pretty sure I installed it while the block was still on the stand (cause it was a pain in the [censored] to get in). So like I said, I'm not sure what exactly I used to reference my mark, but is it possible that I'm just putting too much oil in it and it's burning it? I know I can probably check this by draining the oil and filling it up, but even though the oil pan I have is a 7 quart, does that mean that it should hold 7-7 1/2 quarts of oil with filter? I don't know how much I initially put in, but it was around 7.

 

I'm sure there's a lot more I can add to this that I can't think of right now and there's a lot of checks I should be doing (compression/leak down/tearing the intake off) but the car is 650 miles away and I won't see it until May...just trying to get some feedback right now and things I can try in the future when I DO have the time and access to do it.

 

I know it's hard for anybody to tell me answers, because of my lack of information and so much is going on here, but I mainly wanted to get as many things to check as possible and if anybody has seen/heard/experienced this.

 

Wow...that's really long. Thank you all in advance

 

Ryan Washington

www.RyansCustoms.com

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ok, if you are sucking trans fluid up the modulator, the trans fluid level has nothign to do with it, the modulator has failed, and needs to be replaced .(About $11)

also, Cylinders 6 and 7 would not be affected by the oil. because the oil is being drawn into the other side of the intake.

 

I would check your valve stem seals.. SBC's are prone to them going hard and not sealing any more. otherwise, I'd guess you have a ring problem..

 

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Ryan, I really doubt that it is an issue with the trans modulator. Usually when they go bad when you pull the line you will get some residue of tranny fluid in the line. I have seen that happen on fords a lot. I know I am stating the obvious but it seems like it is common to the rear four cylinders. Looking at your heads it seems like the ports have had some work done, and the sealing area is kinda small. I would consider pulling the intake and check the seal. I have actually seen some of the performance intake gaskets that do not have the metal sandwich reinforcment get sucked into the intake port. Fel Pro even states that some are not for street use. An old trick used to be to dimple along the top and bottom of the intake ports with a center punch, the raised area would grip the gasket better. It is hard to imagine that if you were having issues with the rings or or valve seals it would be on the rear 4 cylinders only not scattered about. What about carb? If you are running a holley could the secondary float level be too high and possibly dripping fuel into the intake and gas washing the rear cylinders? That could cause oil consumption. Do you smell raw fuel in the oil? It would be nice to have access to a borescope. I picked one up for a problem with a Cat 3208 tractor motor and found it really useful for problems like this. Sorry to be so long winded there are a lot of things that could be going on, I hope I helped a little good luck.

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ok, if you are sucking trans fluid up the modulator, the trans fluid level has nothign to do with it, the modulator has failed, and needs to be replaced .(About $11)

also, Cylinders 6 and 7 would not be affected by the oil. because the oil is being drawn into the other side of the intake.

 

I would check your valve stem seals.. SBC's are prone to them going hard and not sealing any more. otherwise, I'd guess you have a ring problem..

 

Thanks Tim, I knew you would chime in!! lol Anyway, I know it was a lot of typing, but yes, I replaced the modulator with a B&M piece about two years ago. And yes, I knew that cylinder 6 and 7 shouldn't of been affected...that's why I think I kinda eliminated that along with any thing with the intake being cracked (unless in more than once place!). Still could be warped though. As for the valve seals...no smoking on startup and I replaced them with brand new Manley valves and my machinist put in brand new bronze guides! I even used the little plastic cap to put over the valve to protect the seal upon installation (and oil).

 

Mike, you really made a lot of sense about the intake gasket. I agree about the valve seal/rings too (I also hope not lol) that this issue would be only on the back four cylinders. I mentioned the same thing in my first post about maybe grinding away a little too much material between intake ports and it makes sense about what you said about the gasket getting sucked in somewhere, which in fact I hope is the real problem!!! lol That's why I posted that picture and when I looked at it again, the rear port divider definately looks thinner than the front one and the other head would have to have done the same thing. That's something for me to check for sure. And a friend once told me an older technican at the GM dealer he worked at used to do the dimple technique for gaskets! I thought he was crazy!! lol

 

As for carb, I'm running an Edelbrock 650 AVS Thunder Series which seems to be running great on the car now. How much did you pay and where did you get your scope? Thanks

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I would take a look at the intake gaskets too, I have read many forums about sealing issues with aftermarket intakes, also see if the bolts for the intake have loosened, with the heat cycles of the engine, I have seen this happen too, esp with an alum intake

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I know I used a criss-cross pattern on the intake as I always do, but I know I didn't torque them, just as tignt as I thought 5/16'' thread bolts should be! I had an issue where I was getting oil puddling around the intake bolts so I removed the intake bolts (only one at a time) and cleaned them and put ARP thread sealer on each one because I remembered they went into the oil valley. I'm still having oil puddling around the intake bolts, but I thought that might be because I couldn't clean the threads out of the residual oil and the sealer couldn't seal.

 

As far as my vacuum goes...I'm running a .500'' lift and 262 advertised/218/224 .050 Comp Xtreme energy cam. I'm not sure if 15'' is suitible for that cam or not. I have plenty of power assist for my brakes. If 15 isn't suitible for my application, then I would also have to guess that my intake seal somewhere in those rear 4 cylinders (both sides) must be weak/not there. lol Guess the best/cheapest thing to do to start is take my intake off and take a look at what I have for gaskets/seal.

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boy Tim...it's getting DEEP lol

 

Ryan, they are 3/8" bolts, but with the expansion and contraction of alum, put a wrench to them just to be sure, the torque spec should be 35 FT LBS, but I always use a 3/8 impact gun nutz

 

 

hey...when I was in the field of doing it everyday...who has time for a torque wrench :lol:

 

 

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Oh okay, 3/8'' that sounds more like it! laugh

Could the block being decked and heads being milled cause an issue without the intake being machined to fit? I've heard of this before, and asked my machinist and he said just check fitment of the intake and see how it looks. I thought I checked it and I "thought" it looked good. Has anybody seen this before? Thanks

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you better believe it!!!!

 

see if the sealing surface (between the heads) is hitting so the intake won't tighten down all the way, ask your instructors at Ferris about that, if you used the rubber seal, get rid of it and seal it with RVT silicone, ferris does have one of the best auto schooling in the country smile

 

surfacing the heads lowers the intake and so does decking the block

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I knew the surfacing would change it, but wasn't sure how much. No, I didn't use the rubber seal at the ends. I used the Permatex grey silicon, which I use on just about everything. It's what we used when I worked at the GM dealer and if they use it, I trust it! Besides the RightStuff, it seems to be some good, tacky stuff.

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Ryan,

I got my bore scope from a local tool supplier, it was around 400 I have seen them a lot higher. I even saw one in the sears tool catalog that was less. That intake that you got from a friend, was it ever cut? That could cause an issue if not done correctly. When we were racing we checked the intake bolts every week, we ran three nights a week and it seemed that we could always get a little movement out of the intake bolts. it seems that small blocks like to wick oil up by the bolts good luck.

 

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The car is home. The oil would have to be coming from the intake bolts because I would think if it was coming from the valve covers, there would be oil puddled up on the seam where the intake meets the gasket which meets the block. Mike, could I borrow your scope? lol j/k That's a lot of money I don't have now, but I'm sure it's a tool well worth it. I'll check with a few guys back at the dealership and see if someone has one.

 

Do you mean by the intake being "cut" that it was machined to fit best? The answer I think is no. I never had any machine work on the intake and it doesn't look like it's ever been machined (even flanges, no obvious machine marks).

 

Thanks for the tips guys and keep em coming if you have more!

 

Ryan

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I think just about everybody will advise you to install your intake without using the end gaskets. Instead they recommend using a thick bead of RTV.

In the old days, there wasn't a reliable product like RTV available so cork and rubber end gaskets were used....I guess the intake gasket kits still include them out of tradition? Who knows, but the RTV always fits, and sometimes the cork or rubber style won't compress enough to allow a good clamp/seal on the side gaskets. Decking and surfacing makes the problem worse. I have seen manifolds down tight against those factory end gaskets and still not making contact with the heads.

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Ouch. And yes, Fel-pro still provides the end seals in the SBC and 4.3 engines. I know at the dealer, we use RTV on 2.8/3.1/3.4 V6s on the ends, but the 3.8's always get much thicker rubber end seals and the 3.8's have much, much less leaky intake gasket issues until they get a lot of miles on them...unless you have one with the plastic upper intake...and I bet you can guess what the problem was there.

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Guest Torquemonster

My 2cents. have a 70 with 400sm 2bbl 65000 miles on the odo All original car ran great. normal oil consumption for it's time 1qt every 2000 miles or so. Decided to install a Comp cams bumpstick kit,Lifters,pushrods,springs,retaners, umbrella seals,Roller tip rockers timimg chain set.did it with the heads on. Everything went smooth & car ran great! But my oil consumption went up, and now my plugs on #6 & 8 started to get oil fouled. started to use 1/2qt every 300-500 miles. Ouch! Not enough to cause a miss but it didn't do it before the swap. Figured I ripped a seal so I tore it apart and replaced the seals and installed the little "o" rings too. Still no good. Did some more research and someone said that even though SBC intakes usually never have a sealing issue look for the teltail signs. Tore it apart and I noticed a trail of something in the head intake runners on those cylinders. Oil residue, shinny wet looking Ha.

I had used a thick Mr G intake set and replaced it with a stock felpro set. Oil consumption is down better than before I installed the cam. Go figure.

Hope that helps.

Frank

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ryan.. of interesting.. the 3800 is only BUICK designed engine in that bunch.. the rest are all chevy designs.. which is why they leak smile buick has always been particular about leaks :0

 

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Guest PrimeredMonte

Before you go ahead and remove the intake, just take a can of aerosol carb cleaner, and spray it around the mating surfaces where the intake meets the heads + block.

Do this with the car running. If you get any change in idle, you have a vacuum leak ie. bad intake seal.

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I've used this technique before on other engines, but if my intake gaskets are sucking in oil from the inside of the engine, the oil galley, why would this show up on this test by spraying on the outside of the intake/gasket/head surface?

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  • 2 months later...

Well here's the latest...before I could do a compression check or anything, my buddie took the cam out while I'm still 600 miles away from the car. I asked him to pay close attention to the intake gaskets when he took them off and he said they were covered in oil. I figured this when I was home for a week and took each intake bolt out at a time and cleaned them off and thread sealed them again since oil was puddling on the top of my intake around each bolt hole. When I went to go tighten the intake, a little oil from the intake gaskets seeped up and out from between the itake and heads.

 

For some reason, my intake bolts don't stay tight. What do you guys do to keep them tight and keep them sealed from oil in the galley at the same time?

 

Also, along with a new cam and lifters, etc; I ordered Fel-Pro's intake gaskets made for aluminum intakes since I was running stock replacements before: http://store.summitracing.com/partdetail.asp?part=FPP%2D1256&autoview=sku

I also ordered Edelbrock's Gasgacinch: http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL%2D9300&N=700+115&autoview=sku

This also says it's for intake sealing surfaces but I still want to use a thin film of silicon around the coolant crossovers.

 

Wish me luck and please send more advice! Thanks

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