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Trifecta

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Discussion starter · #1 ·
They did a final test on my 1968 Pontiac OHC 6 250 Engine. They did a compression test while engine was still warm and Compression stayed at 140 with a CR=10.0:1, and then they did a leak down test on it. Leak down test was incredibly tight. Temp was allowed to creep up to 190 degrees and oil pressure held at 30 psi.
I'm not an expert at this but I think these numbers are damn good. Rochester Quadrajet was overhauled but it will need to be tuned.
Transmission not done yet. Top mechanism works great but interior needs to be completely upholstered. Disc brakes and suspension not done, and dash panel being rewired.
So engine will be wrapped up until ready for it.
Bob

youtu.be/ZwmVGCfGSjO

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Discussion starter · #4 ·
finn210 said:
I have no clue what kind of timing set is on that ohc engine but I'm pretty sure that advancing the cam would make wonders.
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finn210 said:
I have no clue what kind of timing set is on that ohc engine but I'm pretty sure that advancing the cam would make wonders.
Click to expand...
No offense, but when I consider what I started with, I'm already working with wonders. BTW, have you ever seen or worked on one of these scarce OHC 6's? I've never seen another other than the ones I own, so I'm always willing to listen to experienced help. Your suggestion has merit, as it seems to work on other more conventional engines,
Thanks
Bob
 
#5 ·
No offense at all Bob and no I haven't worked on Pontiac ohc engine but yes I have seen one.
An engine is an engine and it doesn't know what is scripted on the valve cover, all I'm saing is that to me 140psi cylinder pressure in fresh build sounds pretty low.
 
#6 ·
Running an engine on an engine stand allows checks for leaks & not much else.
Everyone is concerned about low cranking compression we have a cart before the horse scenario here its a fresh build, take the d a m n thing out for a ride & bed the piston rings in.
One of my 13 to 1 mills only pumped 195 after the rings were bedded in on a engine dyno, it had a big cam with a lot of overlap.
 
#7 ·
Churchkey said:
Running an engine on an engine stand allows checks for leaks & not much else.
Everyone is concerned about low cranking compression we have a cart before the horse scenario here its a fresh build, take the d a m n thing out for a ride & bed the piston rings in.
One of my 13 to 1 mills only pumped 195 after the rings were bedded in on a engine dyno, it had a big cam with a lot of overlap.
Click to expand...
Except cold cranking a fresh engine also tells us if there is any potential or real problems. Ultra low cylinder pressure can be a problem. It would not be the first time an engine builder made a mistake. Hell it would not even be the first time an engine builder made a mistake on one of Bob':s engines.
 
Discussion starter · #9 ·
Robert Haas said:
Except cold cranking a fresh engine also tells us if there is any potential or real problems. Ultra low cylinder pressure can be a problem. It would not be the first time an engine builder made a mistake. Hell it would not even be the first time an engine builder made a mistake on one of Bob':s engines.
Click to expand...
Don't know what engine you're talking about Robert. You've worked on two of my engines. One was the 327 on my Vette. In that case the problem was the end piece of the tachometer cable broke off and fell down inside the distributor and wedged itself between the distributor shaft and outer case and broke the distributor shaft, I still have the pictures you sent me. I allowed you to replace the broken distributor with an MSD HEI conversion. The 327 engine overhaul by Gary Camp in San Diego is one of my best running engines.
The other engine you worked on was the 1600 CC on my Baja Bug. I just had the crankshaft replaced on it. I don't know what went wrong there, but it's running now.
I am OK with the compression numbers I am getting on the OHC 6, and like Churchkey sez, I am not going to worry about it. This is not a race horse, and the even cylinder compression numbers are a good sign for me.
The numbers are open to conjecture and I'm open to opinions and suggestions...thank you all for that.
Bob
 
#10 ·
Trifecta said:
Don't know what engine you're talking about Robert. You've worked on two of my engines. One was the 327 on my Vette. In that case the problem was the end piece of the tachometer cable broke off and fell down inside the distributor and wedged itself between the distributor shaft and outer case and broke the distributor shaft, I still have the pictures you sent me. I allowed you to replace the broken distributor with an MSD HEI conversion. The 327 engine overhaul by Gary Camp in San Diego is one of my best running engines.
The other engine you worked on was the 1600 CC on my Baja Bug. I just had the crankshaft replaced on it. I don't know what went wrong there, but it's running now.
I am OK with the compression numbers I am getting on the OHC 6, and like Churchkey sez, I am not going to worry about it. This is not a race horse, and the even cylinder compression numbers are a good sign for me.
The numbers are open to conjecture and I'm open to opinions and suggestions...thank you all for that.
Bob
Click to expand...
Your oil pump siezed and cut your distributor in half. Upon inspection we determined the wrong pump had been installed. I replaced the pump, welded in the correct pick up and found a tach drive MSD with a Rev limiter that you desired.

140 PSI is low in my own unqualified opinion.
 
Discussion starter · #11 ·
Robert Haas said:
Your oil pump siezed and cut your distributor in half. Upon inspection we determined the wrong pump had been installed. I replaced the pump, welded in the correct pick up and found a tach drive MSD with a Rev limiter that you desired.

140 PSI is low in my own unqualified opinion.
Click to expand...
Rob, I still have the parts. It was the distributor shaft that got jammed up up by the tach drive contact that broke off. I’m not going to debate this any further. No sense. The oil pump was another matter.
I think the compression is fine until I get the car on the road but I do respect your opinion , qualified or not. Let’s keep this fun not funny.
 
Discussion starter · #14 ·
gtxdana said:
Like I posted in your other thread on the low compression test-have you tried a different compression tester or at least replaced the leaking schrader valve in the one you're using to see what numbers you get?
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Nope. It is what it is. If it’s broken, I’ll fix it. I have two more in the wings.
 
#15 ·
Trifecta said:
No offense, but when I consider what I started with, I'm already working with wonders. BTW, have you ever seen or worked on one of these scarce OHC 6's? I've never seen another other than the ones I own, so I'm always willing to listen to experienced help. Your suggestion has merit, as it seems to work on other more conventional engines,
Thanks
Bob
Click to expand...
Seen them in magazines, shows in 80s. Was a cool option, GTOs get the lime light. there are FB groups just for OHC 6. I'd check them out, probably get some invites to shows. PHS ...Pontiac Historical Society?
 
#17 ·
Bob, I don't think anything in your engine is broken. All I'm trying say is that I really think that advancing the camshaft would really help. I've done that mistake and messed up timing set installation the result was that camshaft was retarded and due that cylinder pressures were really low and while the engine (350 sbc) did run and sounded good it was a dog to to say the least.
 
Discussion starter · #19 · (Edited)
It's interesting no one has asked whether I'm using a domed or flat piston. I believe that due to valve travel, they used q "D" shaped .060 recess;. (see pics)
The cam that was on there looked good. It may have had the head overhauled. So they cleaned it and reinstalled it. Everything was replaced in the order it was removed.
Machinist used 1968 Pontiac specs to put it together, and mechanic used the thinnest head gasket he could find online.

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