Asking for Advice Fix 273 or Replace

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RichardJ916

RichardJ916

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ENGINE IS 1967 273 SUPER COMMANDO OUT OF A BARRACUDA WAS REBUILT W/ NO DOCUMENTATION BEFORE I PURCHASED USED.....

This is how the paper work was stated when i got the car, so this is my problem, or question....

The car has been a great car except for a problem that has been driving me nuts over the last few months. There is now a lot of blow by, it burns about a qt. of oil about ever 500 miles. It realy doesnt smoke out of tail pipes but just a lot of blow by. The motor runs strong and I am happy with the motor beeing only a 273 and not a 340. The question is should I take the motor out and rebuild or replace the motor with a new crate motor. I never race it or get into it much and am happy if the motor stays the same meaning to keep the 273. I have the ability to remove the motor and do a rebuild but not sure on what to do.

So my question is kinda easy, should or would I be ok to rebuild or find out why it is has the problem or would you replace the motor.....

What would you guys do......??????

Thanks
 

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If it were me, and I was happy with the way the engine performs, I would pull it and tare it down and see what is going on. If it turns out to be in bad shape I would replace it. But if it can be fixed for a reasonable amount of $ I would fix it.
But it is not me. LOL
 
I suspect there were shortcuts in the rebuild to save money. Some will knurl the pistons skirts rather than buy 8 pistons, knurl the valve guides rather than replace them, etc.. Result is a engine that runs fine for a while. 30,000 miles maybe.
When you get inside that 273 and start measuring things you'll find your answer.
 
If the engine runs good and the blow-by isn't a problem just drive and enjoy. If you decide to pull the engine then you can decide whether to rebuild or replace.
A stock rebuild done right will cost around $3000 and a crate motor will cost more. Your choice. toolmanmike
 
With the ease of finding another motor to rebuild and replace yours with, I would probably build another motor, probably a 318 since they are plentiful, and keep your motor in there until the replacement is done and ready to go in. Then I would swap the motors over and put all your dressup items on the new mill and make it a weekend project!!

2nd option is to remove your motor and get inside and see whats going on in there. Hopefully you will still have the Commando items inside like the solid lifter cam and 10.5/1 pistons. I suspect that maybe when your motor was "rebuilt" they didn't want to pop for the 10.5 pistons, as for a long time they were unavailable and pricey to have custom made. I'm not sure they are even being reproduced now, but I thought I had seen an article that Egge was remanning them. Option 2 is going to see your car down for a while longer, but with winter coming on maybe you have the opprotunity to do so now!!

Did I mention that you could come over to Pinckney and pick up one of these 318's I have for a measly $50.00?? I can even get you close in date to your car's year!! Either way you go, good luck with your decision. I would certainly be looking into it, a quart every 500 miles is a lot of blow-by!! Geof
 
The 273 Commando in my 66 burned a quart every 100 miles, when I pulled it apart, the only thing that looked bad was the valve guides and valve seals. Ran real good. I've run knurled guides on small blocks that ran 300K before they got loose. Blowby sounds like rings are not sealing. If the "rebuild" was a rering, bearings, and a valve job it would make sense. I like 273's, they have a lot of heavy duty parts from the factory and were very efficient. On the other hand, it is nice take your time rebuilding a spare engine and swap them in a weekend...
 
Me i would stay with the 273 I just built a 318 had it zerodecked and all machine work done by shop bored 30 new kb pistons, I put it together myself bought recondtion heaDS from areoheads, I only spent 1800 counting all labor and parts Do you have a pvc vavle that will cause blowby
 
mr.318 said:
Me i would stay with the 273 I just built a 318 had it zerodecked and all machine work done by shop bored 30 new kb pistons, I put it together myself bought recondtion heaDS from areoheads, I only spent 1800 counting all labor and parts Do you have a pvc vavle that will cause blowby
Click to expand...
I have a breather one one side and a PCV on the other side....
The breather is just vented out the botom of the motor....
I most likely will rebuild the 273 commando motor, I still think it has all the correct parts that make it a commando HP Motor.... Strong motor if it wasnt for the blow by,,,,
 
I plan on doing a compression test on all 8 before I pull the motor, I was wondering if this will kinda tell me 1/2 the story, I do know that if the test fails it most likely is the rings and then it will need to be pulled. If the test pass I was wondering if it could be the heads need repaired and rebuilt. Would someone please advise me on what to look for and what path to take, if the compression looks good....
Thaks
 
If I remember right you do a standard compression check. Then to check the rings shoot a couple pumps of motor oil in the cylinder and do the test again if the readings improve much that would indicate the rings are bad. If they don't improve after doing the oil trick probably the valves. Think thats how we did it in high school shop class. I think!

No smoke and blowby sounds like rings to me.
 
RichardJ916 said:
I have a breather one one side and a PCV on the other side....
The breather is just vented out the botom of the motor....
I most likely will rebuild the 273 commando motor, I still think it has all the correct parts that make it a commando HP Motor.... Strong motor if it wasnt for the blow by,,,,
Click to expand...

zhandfull said:
If I remember right you do a standard compression check. Then to check the rings shoot a couple pumps on motor oil in the cylinder and do the test again if the readings improves much that would indicate the rings are bad. If they don't improve after doing the oil trick probably the valves. Think thats how we did it in high school shop class. I think!
Click to expand...

I kinda remember that myself... been a long time class of 77. I will have the neighbor come down and look at it soon, one more car show then retire for the year. I have lots of time to fix for the next years fun. Thanks
 
Here's what I found on Yahoo.com

If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings. If the readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings tells you the cylinder has a bad valve
 
RichardJ916 said:
Here's what I found on Yahoo.com

If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings. If the readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings tells you the cylinder has a bad valve
Click to expand...


That is correct. A compression test done without oil and with oil can help you identify which cylinder is the problem and if it is rings or valves causing the problem.

You can also isolate where is the source with a leak down tester. You pressurize each cylinder and can hear the pressure leaking through the exhaust or intake to isolate which valve(s) may be your problem.
 
I agree with Geof here...

Keep driving and rebuild another motor...

Paul

cosgig said:
With the ease of finding another motor to rebuild and replace yours with, I would probably build another motor, probably a 318 since they are plentiful, and keep your motor in there until the replacement is done and ready to go in. Then I would swap the motors over and put all your dressup items on the new mill and make it a weekend project!!
Click to expand...
 
RichardJ916 said:
Here's what I found on Yahoo.com

If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings. If the readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings tells you the cylinder has a bad valve
Click to expand...

Do you guys think it really should be No change with oil in order to be healthy. Or is some small amount of increase to be expected. I saw 10 PSI increase on mine.
 
Engines wear out everywhere at the same time. You should see a slight increase in compression when adding a squirt of oil. It's sealing the wear in that cylinder. It sounds like a valve problem if you don't see a sizable increase. toolman
 
toolmanmike said:
Engines wear out everywhere at the same time. You should see a slight increase in compression when adding a squirt of oil. It's sealing the wear in that cylinder. It sounds like a valve problem if you don't see a sizable increase. toolman
Click to expand...

The question is what defines "slight" and "sizable".

According to this guy:
http://www.gregsengine.com/cylinder-compression-testing.html

With the above said, you squirt the tablespoon of oil (SAE 30W is fine) into a cylinder that is reading low. Crank the engine two revolutions or so to spread the oil then retest the cylinder. If the compression comes up markedly, 40 PSI or more, the trouble is poor ring to bore sealing. If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head.
​
 
65DartGTConv said:
The question is what defines "slight" and "sizable".

According to this guy:
http://www.gregsengine.com/cylinder-compression-testing.html

With the above said, you squirt the tablespoon of oil (SAE 30W is fine) into a cylinder that is reading low. Crank the engine two revolutions or so to spread the oil then retest the cylinder. If the compression comes up markedly, 40 PSI or more, the trouble is poor ring to bore sealing. If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head.
​
Click to expand...

Looks like Greg at "gregsengine.com" and I think alike only I didn't need to be specific with the compression increase numbers. A tablespoon or a few squirts of oil to do a test like this is not rocket science and is not a specific test but just a generalization. A leakdown test would be more accurate.
 
It might be sucking oil in through the intake ports due to bad intake to head sealing. This can be seen by driving down the road and letting foot off gas. When throttle blades close the vacuum in the intake runners goes up and if there is a sealing problem oil gets sucked in. Blue smoke can be seen coming out of tail pipes but it could burn clean under other conditions.

How do you know its blow by? If you take the breather or oil cap off do you see smoke coming out when engine is running? What makes you think its blow by?
 
I used to have a Breather cap that leaked oil out of it, so I got a breather cap with a hose out of the top of it. I vent it to the bottom of the car.
You can look at picture at the start of this thread....
 
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