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Diagnose 80's sbc issues? 50,000 miles Daily Driver

4K views 30 replies 5 participants last post by  AutoGear 
#1 · (Edited)
I just pulled my engine that I overheated and noticed a few other things when I pulled it and wanted to see if you guys could help me correct the problem. Temps have always seemed to run correct but overheating was caused by the lose of a lower water hose and didn't notice till it was to late, engine started to rattle.:pain:


Engine has 50,000 miles on a rebuild,.030.
90% driving is on Highway- average about 700miles a week.
84 c-10, chevy truck Daily Driver
87 octane
Crate 350/350 turbo set up, 31"tires
HEI- 14 degrees intial,10 degrees vaccum advance, 34 total
Quadrajet
EGR
CCS-2 Mellings Cam SAE Specs@ Gross Center
Duration @.50 Cam Lift Duration Lift valve lift Line
CCS-2 INT. 194 258 .260 .390 108 HYD.
EXH. 202 269 .273 .409 116 HYD
http://www.melling.com/Portals/0/Size Charts/Stock Cam Specification Chart.pdf

Stock engine specs
Horsepower: 249 HP @ 5,000 RPM
Torque: 304 Ft/Lbs @ 3,500 RPM
Compression Ratio: 8.50 to 1
Block: 4 – Bolt, 2 Piece Rear Seal, 4.000” Bore
Crankshaft: Cast Nodular 3.480” Stroke
Heads: Cast Iron, 76cc
Valves: 1.940” / 1.500”
Ok, heres the question/problem. The center of the heads look to be heating up too much and I am thinking the problem might be timing related or EGR related(new EGR)? Heres a photo of what I am seeing. The center of the heads has been BURNING oil at the black area. Seems its been getting hot enough to burn the valve gasket also_Oil changes were done regulary in the begining but lately for the last 3-4 months Ive been loosing a quart of oil every 2-3 weeks from leaks so I just been adding a quart.


 
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#2 ·
Does your exhaust system still have the flapper valve in the passenger side exhaust manifold that directs all the exhaust over to the other side of the engine on cold start-up, by way of that under carb crossover passage??

Looks like what you see when this flapper seizes shut.
 
#4 ·
With no water in the engine, that area of both heads is going to get RRRREEEAAALLLYYY hot, it's the hottest area in the whole engine.

If you are going to rebuild this, figure that valves and springs right there are toast, heads will likely need milled flat...if they aren't cracked. Block deck probably not flat there anymore either. Wouldn't trust those 4 rocker arms either.

Piston skirts are likely collapsed also, from your description of noise.

I'm trying to recall, but seems like with no heat riser valve, the intake gasket with the hole in the crossover passage should have been fully blocked?? To allow some heat up there and some for EGR, but not a full crossover of gasses?? Gaskets should have come with a couple different metal inserts.

Anyone else remember how this should be??

Fel-Pro head gaskets used to come with a instruction sheet showing drilling a new 3/8"-ish hole in the block and head to match one hole in their gasket, for better water transfer through that hot area between the two exhaust valves. Some blocks already have the hole, some don't.....maybe that is an issue.
 
#5 ·
Its a little hard to believe that the black burnt oil was caused with minutes of loosing water . Seems like it would be some thing that would take longer to cause. I think you are right about the valve train being trashed but it is also identical on the other side of block.
 
#6 ·
I am leaning towards the EGR as to whats was causing the severe heating in the areas over the center of the head. But what could cause it to heat up so much? I was running the EGR thinking it would help a little with MPG but causing heat issues like that I guess I would just want to eliminate it?
 
#7 · (Edited)
I did find this .
Using a relatively mild camshaft and compression ratio matching the cam, if using an EGR valve, more vacuum advance may be needed to compensate for the diluted air/fuel mixture it causes- much the same condition that a cam having a lot of overlap can cause. You may find as much as 16 degrees of vacuum advance is needed with a relatively mild cam if an EGR system is used.If there is no EGR being used, the amount of vacuum advance needed will be around 10-12 degrees. http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor
I am running 10 degrees of vacuum advance WITH a EGR????
 
#8 ·
. That's a stock, basic, all iron SBC 350... they're pretty tough... a little overheating prolly didn't hurt the basic engine, but the excess heat did shrink the intake to head gaskets, causing all kinds of leakage of oil, vacuum, and coolant there...

. As mentioned, Chevy V8's have the interior two exhaust valves side by side creating a well known hot spot in the engine... many other engine brands also had that problem... not a big problem in stock basic engines... latest engine versions separate those two valves (LSx, etc.)...

. DO a compression check on all 8 cylinders, if all cylinders up good and even in compression, I'd just put it back together re-torquing the head bolts to spec. and with new intake to head gaskets... if compressions not even, prolly need new head gaskets as well...
 
#15 ·
DO a compression check on all 8 cylinders, if all cylinders up good and even in compression, I'd just put it back together re-torquing the head bolts to spec. and with new intake to head gaskets... if compressions not even, prolly need new head gaskets as well...
. Forgot to mention, valve seals may have melted from the heat, so good idea to replace them...

. Also, that Melling 194/202 cam is identical to stock basic Chevy original cam... I wouldn't go any bigger in cam size, unless also increasing the compression ratio... since this is basically a pathetic early 1970's engine design, which got poor MPG, low power, low torque, if you weren't in a hurry, I'd be putting better pistons in it than the stock dished ones with low 1.548" 'compression height'... like 1.560" height flat top pistons... to go along with those big 76cc chamber heads... change the camshaft timing to 'straight up'...
 
#9 ·
I just measured what I should be getting for vacuum advance and it looks like I was wrong on how much I was running. I should be around 16 degrees of vacuum advance like the article states for use with a EGR. I could of swore I was running 10 degrees but I set this up 2 years ago.
 
#10 ·
. Vacuum advance is for additional advance for part throttle cruising MPG...

. This engine prolly needs 14 initial plus 24 centrifugal advance = 40 total at WOT little to no vacuum...

. The actual ~7.6:1 static compression ratio and bathtub chamber heads usually like a lot of ignition advance to make peak HP...
 
#11 ·
I just pulled my engine that I overheated and noticed a few other things when I pulled it and wanted to see if you guys could help me correct the problem. Temps have always seemed to run correct but overheating was caused by the lose of a lower water hose and didn't notice till it was to late, engine started to rattle.:pain:


Engine has 50,000 miles on a rebuild,.030.
90% driving is on Highway- average about 700miles a week.
84 c-10, chevy truck Daily Driver
87 octane
Crate 350/350 turbo set up, 31"tires
HEI- 14 degrees intial,10 degrees vaccum advance, 34 total
Quadrajet
EGR
CCS-2 Mellings Cam SAE Specs@ Gross Center
Duration @.50 Cam Lift Duration Lift valve lift Line
CCS-2 INT. 194 258 .260 .390 108 HYD.
EXH. 202 269 .273 .409 116 HYD
http://www.melling.com/Portals/0/Size Charts/Stock Cam Specification Chart.pdf

Stock engine specs

Ok, heres the question/problem. The center of the heads look to be heating up too much and I am thinking the problem might be timing related or EGR related(new EGR)? Heres a photo of what I am seeing. The center of the heads has been BURNING oil at the black area. Seems its been getting hot enough to burn the valve gasket also_Oil changes were done regulary in the begining but lately for the last 3-4 months Ive been loosing a quart of oil every 2-3 weeks from leaks so I just been adding a quart.


Referencce picture number 1 do both heads look like this?

This is classic overheat damage for this engine. This is the hottest part of the engine where not only are the exhaust valves paired which makes a heat concntration but also the passages for the crossover originate here. So more than anyplace in the engine except for the exhaust manifolds themselves there is no hotter location and this got hot enough to coke the oil. I'd recommend taking the heads apart and getting them magnafluxed. This under normal circumstances is a crack and warp prone area. Running even brefly without coolant usually cracks and warps this zone. The block also could stand checking while not usually cracking here unless it's a 400; this heat affected area often warps.

You're just goin to have to invest some money into finding out what the condition of these parts is. My gut says these heads are toast, but you might be lucky.

Bogie
 
#12 · (Edited)
Yes , both heads are the same. The engine was pulled and at machine shop. I should hear tomorrow what the damage is. I am not really thinking the black burnt oil is caused solely by the overheating. The valve cover gaskets and intake gaskets were toasted in the same area. The engine had started to leak oil and have a exhaust leak in the last few weeks I am thinking now from the gaskets getting burnt up prior to overheating.
It will get fixed again , but now need to figure out whats causing so much heat in 50,000 miles. I dont really have time for a lot of testing since this is my daily driver I have to get it up and running ASAP.
 
#13 ·
It will only take a couple of minutes from the time of the hose giving out and near complete water loss until it is hot enough there to make it look like that...if you ran it long enough without water until it started to rattle it will easily look like that, and cook everything near those points. Just 3-5 minutes will do it.

Cork valvecover gaskets will look cooked in this area at 50,000 miles anyway, especially on a loaded van or truck, or something that pulls a trailer fairly regularly.
 
#16 ·
If it was me; I'd get different heads, its not a bad time to upgrade the motor a little bit assuming the shortblock is sound. Pull the heads and check that the block deck isn't damaged, probably not, but the heads are coming off regardless. Perhaps a mild cam upgrade since you're replacing the valvetrain. However, Im worried the pistons may have been damaged.
Post the casting number on your heads and we can recommend some cost effective heads as replacement. Normally I'd suggest Vortecs, but that would require changing the intake manifold with a vortec specific one. There are plenty of readily available Non vortec heads for 350 chev's.

Whats your budget on this and your skill level? If the pistons are damaged, you're at a crossroads.
 
#18 ·
Yea I gotta get this thing back on the road and the budget so far is about 600 for a complete rebuild if the damage is bad. I do have other set of heads if these heads are bad.

I really dont expect much from this engine but as close to maintenance free as I can get and fuel mileage. I have other projects and dont need another with this one. BUT,,,, If heads on this engine are bad I might be forced to do some thing else. I do have a set of 041 heads that are 58cc 2.02 valves, ported and polished:D I also have another set of I believe 305 heads that are 65cc's with 1.94 valves , bought them from Aerohead years ago but only ran them for about 500 miles. These are not really any better for flow than what I have now but do raise compression. I also have another set of heads that are identical to what I have now that would need to be redone.

But again , this is the daily driver and occasional tow truck that I dont want to be messing with besides changing oil.
 
#26 ·
If the heads you are going to use are the 76-78cc "smog" castings, I would use flat-tops, as compression ratio isn't close to the listed 8.5-1 for the usual crate engine/stock 70's early 80's engine, more like just 7.8- 8.0 to 1.

Do you have the head casting #, or know the head cc??
 
#27 ·
the heads are 76cc since it needs a complete rebuild I am going to "upgrade" a little. Looking at this cam with 4 valve reliefs flat tops. Hopefully I can still use 87 octane


Cam Style Hydraulic flat tappet
Basic Operating RPM Range Idle-4,500
Intake Duration at 050 inch Lift 204
Exhaust Duration at 050 inch Lift 214
Duration at 050 inch Lift 204 int./214 exh.
Advertised Intake Duration 278
Advertised Exhaust Duration 288
Advertised Duration 278 int./288 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.420 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.433 in.
Valve Lift with Factory Rocker Arm Ratio 0.420 int./0.433 exh.
Lobe Separation (degrees) 112
Computer-Controlled Compatible No
 
#28 ·
Damn I didn't do too bad for a gearbox guy...LOL "BuzzLOL" how about double or nothing??

OP : Sorry you blew your motor, and your budget...but now you can have a better performing engine and the peace of mind that you put together something with a solid foundation, and learned something in the process. Keep us posted!
 
#30 · (Edited)
. LOL! When I hear overheat 'rattle', I immediately shut the engine down and fix the problems to save the engine... apparently the OP didn't...

. Using typical rebuilder* 4-eyebrow flat top pistons in a 355" engine with rebuilder .050+" thick composition head gaskets under 76cc heads... plugged into Summit Racing's handy compression ratio calculator... I was surprised to see compression ratio still down in the 7:1's...!!!

. Rebuilder pistons are usually supplied with early 1970's slug engine 1.548" compression heights... but... IF you ask, can usually be the better 1960's 1.560" heights at no additional costs...

. Plugging 2-eyebrow flat top 1.560" pistons and .015" thick head gaskets into the above engine gives a compression ratio in the low 9:1's... and better engine quench effects... what I consider minimum for the efficient use of the OP's desired 204/214 cam... 87 or maybe 89 octane gas needed... 4-eyebrow 1.560" flattops might get the engine closer to 8.9:1 and 87 octane only...
 
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