My son's 1968 Chevy

[dbrannon79]

Well as you guys have head, my son bought him a 1968 chevy C10 with a 250 straight 6 and 3 speed manual trans (floor shift) that has TBI installed from a company called Dynamic EFI. the company has since gone out of business with the owner passing on. There is not much info out there on this setup other than finding resources on their old website through the way back machine and a couple of forums where the owner was active in before his passing. I'v listed his truck in my signature for others to see.

Here are some pics of it when he bought it.

 

[dbrannon79]

I have been helping him work on the truck trying to get it to the point where it's mechanical safe and good for an every day driver. have already done lots of tuning on the ECM along with repairing several odds and ends that it needed to run and get closer to that goal.

some of my posts are on other threads but I figured I would start off with a new thread here on furthering that work.

Just yesterday I took him out in the truck so he could start learning how the shift it since he has no experience with a stick, but after a good while of putting around in an open parking lot and trying to drive across town, it broke down on us. we got it home and I figured out that the ignition module in the HEI dist had failed.

Now proir to this, I have been driving it here and there and noticed that it seems not to have much power, it can't really take off from a light very fast nor does it have hardly any acceleration. it will build speed just seem down on power.

runs smooth without any missing so I stupidly dismissed the simple things like spark plugs and whatnots.

Well this changed today.

 

[dbrannon79]

with knowing the ignition module will cut out after it get hot, it still runs fine. today I decided to pull it around to the back driveway and do some simple things like have a look at the spark plugs and even do a compression test to see the overall health of the engine. mind you this engine was fully rebuild at the local machine and engine shop here in town years ago and only has about 7600 miles on it since that rebuild.

the first three plugs looked good but had some carbon on the tips. the back three were completely gummed up and fouled with oil and carbon.

Hmmm.... I pulled out my compression tester and got this...

#1 = 170
#2 = 170
#3 = 170
#4 = 60
#5 = 0 zero
#6 = 70

Now I'm getting concerned and thinking bad rings and a blown piston or burnt valve. I wanted to have a look at the cylinders but could not find my bore camera anywhere so I pulled the valve cover to see if something was up under there...

do yall see anything wrong with these photos?

 

[dbrannon79]

Yes this thing has been running on three cylinders for a while from the looks of the plugs. funny thing is it doesn't miss and runs smooth even trying to goose the throttle while sitting still.

from what I can tell, three of the studs on the head holding the rockers have pulled up, I can easily see the three studs are higher than the others.

I really hope there is a fix for this without having to pull the head. the push rods on these three are also very slightly bent. wiping them off and rolling them on a flat surface I can see a slight bend, also the push rod on #4 has a indentation on the ball end where it was slapped a time or two. hope a valve is not also bent, this cylinder had no compression at all.

you guys know if there is a repair for the studs pulling out of the head? I assume a thread repair kit would be needed not unless there is a longer stud and maybe some extra threads further in the hole that can be used. IDK. both my son and I are bummed to find this.

 

[dbrannon79]

Just reading online trying to find a repair, I am finding out that the studs may not be threaded into the head. I always thought they were threads in there. I can't specifically find that info on a 250 L6 engine though.

 

[dbrannon79]

Here is a pic of the plugs for reference. starts #1 through #6 right to left.

 

[dbrannon79]

Trying to ID the block and came up with this.. block casting number is 3921968 date code is H157, other code is CON2

From what I found the casting number can be a GM 250 or 230,

Date code H157 shows the 8th month, 15th day, 7th year of the decade. Meaning August, 15th 1967

Code CON2 is conveyor #2 in the GM plant

I cant see the vin code stamp that should be on the dist boss, doesn't look like anything is stamped there so I cannot verify if this is the original engine to this truck.

 

[dbrannon79]

Rockauto shows press-in rocker studs for this engine. both standard and oversize. Not sure if this is a repair that can be done on the truck or even on the bench. may have to be done at a machine shop. I saw where the studs can be pulled with a nut and stack of flat washers and might be able to be re-installed by freezing the new stud and heating the boss on the head, but not all that sure it would hold.

 

[ak diesel driver]

I would check and see if they're the same studs as a sbc. If so you could get screw in studs for it. It would be better to do the threading with the head off but probably could be done with the head on if you're really careful. I wouldn't try replacing with press in, those holes are probably messed up. Most of the stud failures happen with stronger valve springs and higher lift cams. If you really wanted to cheap out you could hammer them back in then drill and pin them.

 

[dbrannon79]

I had been looking at the pinning process. from what others are showing online, they are different than the SBC studs, but I've never messed with rocker studs before. as far as drilling and pinning with an 1/8" roll pin, I can access the bosses on the head. Just not sure I want to try.

I have a gut feeling that #4 piston kissed that valve, the head would have to be removed for that part. I can pull the head without pulling the intake or exhaust manifolds and replace the valve if needed.

also it's on my mind wondering now that three studs are like this, what's to come of the rest. and what may have caused this. we don't know if this just happened or it's been like this for a while. when the ignition module started acting out it did pop and spit from the intake a few times, I wonder if the backfiring might have done this as well. looking at the plugs, it's been like this for some amount of time, but then again we did drive this truck out on the freeway for about a 100 mile round trip last month. I doubt it would have had any power nor would have made that trip in this condition then.

Threads on the studs are 7/16-20 from looking at RA. I need to look and see what the press in side size is and compare to the threads on a SBC stud. how hard is it to thread cast iron? If I were to find studs that would work where I just need to use a tap to cut some threads in the bosses that would be I think easier than trying to drive in studs or pinning them. I would be afraid of cracking the cast on the head!

 

[dbrannon79]

I may be mistaken, it looks like the factory studs press in are 3/8" and SBC studs come in 7/16" and 3/8" threaded. the lengths look like they might work but the 3/8" thread going into the head might be the issue if the hole is already that size. I have not tried to remove any of the rocker nuts yet. I may do that tomorrow and measure them to be sure, also the length sticking out of the head on a good one.

maybe the hole can be tapped to 7/16". I think I saw some on RA that was 3/8" on one end and 7/16 on the other.

 

[ak diesel driver]

RA shows them being the same size as the SBC. They also show a .003 oversize probably for this situation. If you pulled out the old ones heated the head and cooled the stud you might get them in

 

[dbrannon79]

Wouldn't 30 over studs require machine work to the head? I was wondering about that. I measured 0.003 on my caliper just to see a visual on how much that was, I would be afraid that once the stud warmed up and expanded it would crack the cast boss.

 

[dbrannon79]

I pulled the rockers off from the #4 cylinder to have a better look and this is what I found. This looks like it’s been this way for a long while. The base of the intake valve rocker stud has wear and so does the top of the boss where the rocker sat rattling around. There is also marks on the exhaust valve spring cage where the intake rocker was striking it. The threads on both studs don’t look great ethere. The exhaust valve studs was just fine, hadn’t pulled up. I just pulled the rocker to get a better look

 

[dbrannon79]

Measured the studs. they are in fact 3/8" studs that stick out from the head 1-11/32" from the top of the boss. thread height is 3/4"

these are the measurements I got with my caliper: 0.372" diameter and the base, 1.342" height from the boss (good stud), and 0.753" thread height

I need to gather this info on SBC threaded studs to see if that is an option, but it's looking more and more like this head will need to come off, be stripped down and sent to a machine shop to have them all replaced.

 

[dbrannon79]

Here is my RA shopping list so far. I don't see head bolts listed or replacement valves. Not sure if these head bolts are reusable or have to be replaced. I have a good feeling I will need to replace the intake valve on #4 but the head will need to come off to check for damage unless I find my bore camera to have a look at the piston top.

 

[dbrannon79]

I will need to contact the local machine shop to see what they will charge for this as well as their time frame. this is the same machine shop that rebuilt this engine several years ago. looking at the #4 intake rocker stud wear up on the shaft just past the threads comparing to the exhaust stud, that stud must have pulled up not long after the engine was running after that rebuild. there is hardly any wear where you can see exactly where the rocker ball was on the stud.

I'm sure they are gonna want to magna-flux the head and check it prior to doing any work on it. Not sure what the cost will end up being. wondering that comparing to finding another head. if they end up doing the work, I will ask about pinning the studs as well so this never happens again.

 

[dbrannon79]

Just got off the phone with the local machine shop. they can fully rebuild the head, and machine the head for screw in studs for a ball park of $500 to $600 with about a 3 week turn around. All I would need to do is pull it and bring it in.

Will talk with my son and see if he agrees, but I think this is the better route to go.

 

[dbrannon79]

Just a curiosity, do you guys think I should pull the engine out and do any more inspections on it while the head is off and at the machine shop or just pull the head? I know it would be much easier to work with on a stand, but wondering if I should also drop the pan and look around in there too. I don't want to open another can of worms but I also don't want more surprises after getting the head redone.