I did what I was scared of today

[stevenfromtexas]

well, as the title says....

i did a compression test today..... .....and yup....not good
the reason being....the pickup would not fire at all. i checked everything you guys mention in older post. all 6 plugs had a good spark, carb was spraying nice, pump was working great. i even re-did the valve lash....nada i checked the wires for the correct order several times. my wife thought i was strange when i kept saying "too young, too old, just right"

question for you guys. i've read through the search bar about doing an "in-frame". not too many guys recommend it and i totally understand. BUT, i have a total of about 5 hours running time on this engine and 1.3 miles on the pickup. I'm a rookie but it seams like the crank would be ok to stay in. if a new set of rings, which i can't imagine not needing them with these numbers, would you guys do an inframe ring job?

When i rebuilt the engine about a year ago i thought i was being thorough and "thought" i did everything by the book/manual. so, please hep me with some knowledge of why in the heck is 4, 5 and 6 as clean as the day i put them in??? the cylinder walls still have the cross hatching in them too. my compression test confirmed it this morning with:
#1@ 105
#2@120
#3@110
#4@ 70
#5@ 95
#6@ 90


'67, 250ci

[Grumpy old man]

Are you sure you have the timing correct ? looking at the picture your dist is off ,

[supercheyenne]

I'm certainly not the most knowledgeable but....

A) I don't think 5hrs runtime is enough to set your rings.

B) I understand your frustration but I'd be reluctant to do a tear down at this stage. A vehicle with those PSI's should still fire and run just fine. It might smoke but it should run just fine. This leads me to believe your problem is elsewhere.

Now since your at this stage.... I guess carry on! I'd ask coworkers, neighbors, fellow club members, someone who can peak at it with you along the way.

[stevenfromtexas]

it has run prior to this. 6*BTDC

frustrated!!! i had high hopes to be on the road by june

[stevenfromtexas]

Originally Posted by supercheyenne

I'm certainly not the most knowledgeable but....

A) I don't think 5hrs runtime is enough to set your rings.

B) I understand your frustration but I'd be reluctant to do a tear down at this stage. A vehicle with those PSI's should still fire and run just fine. It might smoke but it should run just fine. This leads me to believe your problem is elsewhere.

Now since your at this stage.... I guess carry on! I'd ask coworkers, neighbors, fellow club members, someone who can peak at it with you along the way.

thank you sir! actually there was not any smoke. that was leading me to believe i was on the right track guess i shouldn't have "set a date" for cruising'

[gvw5400]

I agree with supercheyenne, I doubt that the rings are seated.
On my past rebuilds I would drive it at different speeds for an hour, then floor it hard for 15 to 20 seconds and then lift off the gas pedal and let it coast with no throttle for a full 30 to 40 seconds. This forces the rings into the cylinder hard then allows oil to be pulled into the cylinder for lube. Repeat 10 times and plan your trip to hang out at a restaurant for 2-3 hours to let the engine cool to ambient temp. drive home, enjoy!!!

[Racer382D]

Compression test results, while not ideal..... aren't too far off to keep it from running... should have done a cylinder leak down if possible, then diagnose from there.

['68OrangeSunshine]

The right break-in sequence for a Chevy L6 runs something like this:
[Use a lot of Black Moly cam grease on internal parts]
Fill crankcase w/ 6 qts [292 specs] 30 weight Non-Detergent, non-synthetic oil.
Pre-spin oil pump drive with electric drill motor/distributor shaft until nominal oil pressure comes up. Install distributor.
Start engine, run 20 - 30 minutes at variable speeds from 1500 - 3000 RPM.
Run truck 'gently' for 500 miles, staying off freeways, No high RPM runs.
After 500 miles change oil and replace with regular detergent oil. [I like Valvoline VR1 Racing SAE 30.]
Now no restrictions on speed.

As for your low compression on last 3 cylinders -- you torqued the head down as per Engine Overhaul Manual specs? Installed rings so gaps on successive layers are 120* or 180* opposed?

[stevenfromtexas]

Originally Posted by '68OrangeSunshine

The right break-in sequence for a Chevy L6 runs like this:
[Use a lot of Black Moly cam grease on internal parts/]
Fill crankcase w/ 6 qts [292 specs] 30 weight Non-Detergent, non-synthetic oil.
Pre-spin oil pump drive with electric drill motor/distributor shaft until nominal oil pressure comes up. Install distributor.
Start engine, run 20 - 30 minutes at variable speeds from 1500 - 3000 RPM.
Run truck 'gently' for 500 miles, staying off freeways, No high RPM runs.
After 500 miles change oil and replace with regular detergent oil. [I like Valvoline VR1 Racing SAE 30.] Now no restrictions on speed.

As for your low compression on last 4 cylinders -- you torqued the heads down as per Engine Overhaul Manual? Installed rings so gaps on successive layers are 120* or 180* opposed?

thank you for your reply.

as far as the torque, yes sir....95# and placed gaps according to my haynes book

[stevenfromtexas]

you guys have forgotten more than i'll ever know. I'm leaning to a gasket kit and trying everything again. my lack of patience and wanting to get on the road is getting the best of me.

so, you guys think the low compression on 4, 5 and 6 ; i should be patient with?

['68OrangeSunshine]

Did you work with a machine shop during your pre-assembly phase? You might have them check the head for cracks, since it's off. Run a staight edge on the top of the block. If not perfect, the machinist will have to shave it.

No. I think you should have much more even compression on all cylinders, like 120 psi all around. That you don't suggests an air gap.

[stevenfromtexas]

i will drop off the head to be looked at. that's the only thing i haven't done on my own; was the machine work. i was concerned about the valves after looking at them. a few of the them don't look like they sit in their seats as well as some of the others.....if that makes sense.

[Steeveedee]

Your engine is not broken in yet, as has been mentioned. Did you follow any kind of cam break-in protocol? I'm not seeing it in the OP. If it were mine, I'd have the head checked (as recommended, though I don't see any indication of a gasket leak), and put it back together. The three cylinders with no ash indicate a potentially extremely lean condition, but #2 & #3 cylinders have some deposits. That's kind of strange, with a 1-barrel carburetor, since it should feed all equally. You don't have a rag stuffed in the manifold portion that feeds the last 3, do you? I've seen things like that. I'd highly recommend you find someone on the board near you to help.

[stevenfromtexas]

Originally Posted by Steeveedee

Your engine is not broken in yet, as has been mentioned. Did you follow any kind of cam break-in protocol? I'm not seeing it in the OP. If it were mine, I'd have the head checked (as recommended, though I don't see any indication of a gasket leak), and put it back together. The three cylinders with no ash indicate a potentially extremely lean condition, but #2 & #3 cylinders have some deposits. That's kind of strange, with a 1-barrel carburetor, since it should feed all equally. You don't have a rag stuffed in the manifold portion that feeds the last 3, do you? I've seen things like that. I'd highly recommend you find someone on the board near you to help.

thank you for your reply. hahaha no sir, no rag

ok, im gonna drop off the head this week.

the break-in procedure, it has been a while since i built it. i don't think i ran it for 30minutes at 1500RPM i'm pretty sure of that i hope i haven't flattened the cam

[stevenfromtexas]

Originally Posted by Steeveedee

I'd highly recommend you find someone on the board near you to help.

i've seen a couple of old post in the search box from guys in my area. i haven't seen them posting much anymore.

Waco, Texas area

[Steeveedee]

Originally Posted by stevenfromtexas

i've seen a couple of old post in the search box from guys in my area. i haven't seen them posting much anymore.

Waco, Texas area

Might be someone to help you. Just be patient.

[HO455]

Proper break in is one of those misunderstood subjects. With a non roller cam engine you have to devote the first 20 to 30 minutes to breaking in the camshaft. Depending on the lift and spring pressures you may have to run specific break in springs to prevent lobe destruction. Once you have successfully broken the cam in and replaced the break in springs if used. Checked your valve lash and brought the engine up to temperature. Now the controversial part begins. Every manufacturer and most machine shops tell you to drive the vehicle conservatively, taking it easy. The reason is simply if there are any questionable clearances in the engine they will wear themselves into spec if they are not overly stressed. And let's say a rod bearing is too tight the bearing will wear and gain enough clearance to live. But if your loading the engine and turning the RPM up, the tight spot may get hot and the babbet will start transferring leading to failure. Then the builder has a warranty issue on their hands However to properly seat the rings you must fully load the engine.
When talking about seating rings what do we mean? It is the process to obtain the balance between perfectly smooth cylinder walls that allow complete ring contact and optimal sealing and the need to keep the cylinder, piston and rings lubricated. The need for lubrication requires that the cylinder walls are not perfectly smooth. A properly broken in cylinder wall will have bumps and valleys like sandpaper, but with a microscopic grit. This allows oil to be trapped in the valleys and the bumps to seal against the rings. This ratio of low and high on the cylinder walls doesn't happen by chance. The rings are manufactured with specific materials to wear against the cylinder walls during the break in period. Then a specific honing process is matched to the rings used to obtain a specific finish on the cylinder walls. The idea is that when the honing is finished the cylinder walls are like a new piece of sandpaper with sharp peaks on the bumps. During the break in process those sharp peaks are worn off by the rings. So the broken in cylinder wall peaks are now flat tops that are surrounded by valleys for oil. Too much ground off the tops gets you more power with less oiling and shorter engine life. Too little removed from the peaks means low power and high oil consumption. The window for this grinding to happen is fairly short as the freshly honed area starts soft and gets harder from heat and work hardening and the ring surface coating is worn away. Once this has happened there is very little one can do to correct break in issues short of starting over.
Nowdays manufacturers now days have very sophisticated honing process's and rings developed to seat very quickly under light loads with the selected cylinder wall material, and computer controlled break in systems. But our old engines don't have access to that kind of technology when we rebuild them. So we have to do it the old way. That means the rings have to be forced against the cylinder walls during the break in. The physical ring tension in the ring is not nearly enough pressure to force the ring against the cylinder wall and grind those peaks off. The pressure needed to do that comes from combustion pressure that has made its way along the side of the piston shoved the ring down against the ring land and once behind the ring forces the ring outwards against the cylinder wall. The more combustion pressure the more the ring pushes against the cylinder wall and removes the proper amount of material. (Assuming that the honing was done properly and matches the ring style). The only way to get maximum combustion pressure is to completely fill the combustion chamber with fuel/air mixture. That means wide open throttle.
I know this is opposite of what many people believe to be true but to get the best sealing rings you must have high combustion pressure. When race engines are broken in they are idled for a very short time to get the engine up to temperature, then brought up at controlled rate several times in ever increasing levels until full power pulls are achieved. This level is usually reached with less than 5 minutes of run time on a roller cam motor. They are confident in the machine work and assembly process of the engine so they are not worried about problems coming from improper tolerances. Taking your new engine out and doing second gear pulls on a empty road are how we us folks don't have dynos achieve the same results. Start with a 1/3 throttle pass to letting up about 30% below red line then repeat with a 1/2 throttle to 20% below red line, then 3/4 throttle to 10% below red line. Then 3 full throttle pulls to red line will do the trick. This is the best reason to blueprint your own engine. Knowing everything inside is to the proper tolerances will make this a fun event not a stressful one.
Having been involved in many dozen large Cat diesel post overhaul dyno break in sessions if you know your assembly is right you will have nothing to worry about. When we dyno a 2500 HP 12 cylinder engine it is started up and pressures are checked when everything is in spec the engine is brought up in RPM steps and once it is up to temp and full RPM the engine's full load is applied to the engine and then held for the rated period. For our continuous duty engines that means 4 hours at full load. Standing next to one these engines for 4 hours is not only deafing but boring.
Failure to meet the conditions means you will not get the required amount of material removed from the peaks of the cylinder walls for proper ring sealing.
I hope this isn't too long and boring.

[57taskforce]

Good advice! I build natural gas compression engines for a living, anything from nat gas turbo 5.9 Cummins to turbo 3306 cats, hell we even have some dinosaur wakeshas laying around I’ve been thru. I more or less do what ho455 stated above. I usually let it get a little heat for a minute or two on the test stand while I make sure the timing is right and I don’t have any leaks or anything else bad going on. then it’s straight to higher rpm pulls in succession as stated above. One thing I’ve had good luck with is trying to keep engine heat between 210-230*. I’ve found that the heat seems to help seat the rings a little better. In looking at your back three cylinders something clearly is a miss.I doubt it’s your rings. To me the piston tops and cylinders look way to clean to have weak rings there’s no burnt oil or carbon deposits. Other than the little bit of carbon on the heads it looks to me like it’s not getting any/enough fuel. Those compressions numbers while weak should be enough for it to run. you say your valves don’t look like they are sitting in the seats right. What was done to the head when you had it rebuilt? Was it a full on rebuild? Im interested to see what your machinist finds when he looks it over. I’m thinking your loosing compression thru the valves.

['68OrangeSunshine]

HO455: Damn, that's impressive. I learned something new.

[Knight72]

Originally Posted by stevenfromtexas

you guys have forgotten more than i'll ever know. I'm leaning to a gasket kit and trying everything again. my lack of patience and wanting to get on the road is getting the best of me.

so, you guys think the low compression on 4, 5 and 6 ; i should be patient with?

When I feel a lack of patience, I sit it down and walk away for a bit. Has saved me from many costly potential mistakes and broken parts/bolts.

[HO455]

Waukesha now that's a name I haven't heard in decades. We replaced the last pair of those in the early 90's. They were old and parts had become such an issue. I don't remember what model they were. About 800 HP diesels . V12 maybe? Went to Cat 398's. A small bump in HP and parts were easy to get.
Thank you everyone. I glad it was clear enough to understand. It's hard for me to grasp things like this without pictures.

[70STOVEBOLT]

Diesels are s little different than gas engines. I used plasma rings in my 402 they will break in pretty quickly. Diesels use chrome rings which are hard and need to be broke in under a load. I broke in my rings and my flat tappet hydraulic cam by bringing the RPM up to around 1500 and then alternating between 1500 and 2000 for 15-20 minutes using SAE 30 non-detergent motor oil with a pint of STP oil treatment. I ran it for about another 40 minutes at various speeds on the road and then changed the oil. Refilled with SAE 30 and a pint of STP again for 500 miles then switched to 10W30. I honed the cylinders with a battery powered 19.2 volt drill and a ball hone. So far so good.

[mike16]

make sure your head is not warped.

I have seen people do funny things to save a buck .

retorqueing cylinder head bolts requires a procedure just like other aspects of the break in procedure. to do it all properly almost becomes an art form rather than a procedure.

[dan s]

Those numbers could easily be caused by improperly seating valves.

[dan s]

Also are you sure that carb isn't dumping fuel?, front 3 cyls look like soot in the head and the rear three could be gas washed( which will cause low compression)