Flathead V8 smokes..........

[C Carl]

.................... upon startup after sitting for a month or two. I understand why this happens with a OHV engine, but I can’t explain this. Car is a 1925 Cadillac. Strong performing engine, good oil pressure, does not smoke underway.My somewhat tired 1924 Cadillac doesn’t blow a cloud of smoke no matter how long it sits. Does run strong, good oil pressure, bearings in VGC, but does smoke some underway.

 

I am helping a gentleman who has some interest in purchasing the car which is a couple thousand miles from me. Is there some explanation which might help shed light on the engine condition ? I would imagine seller would not object to a compression test. Of course we would really like to know the condition of the bearings. Usual hearsay claims of significant engine work recently done, no first hand testimony, no receipts, maybe about 60-70,000 miles on the timing chain by stretch measuring which is very easy to do on these cars.

 

  Thanks for any and all help. I hope one of you flathead experts can provide insight where I am blind.    -    Carl 

[JV Puleo]

I had a similar problem with my '27 - one I never was able to fix but I was in my 20s at the time and had very little experience. The gentleman I sold it to was a very competent mechanic (he'd been a Spitfire mechanic with the Eagle Squadron in the RAF early in WWII)...I was later told that he just carefully adjusted the valves and that cured about 90% of the smoking problem.

[Rusty_OToole]

Do a compression test and check the oil pressure. Also, verify that it is not full of heavy oil or STP.

[hidden_hunter]

Valves would be my guess to, the combustion chamber design seems like it would cause everything to settle back on the piston tops 

[padgett]

"stretch measuring which is very easy to do on these cars. " agree - all it takes is a breaker bar on the crank and a delicate touch.

[Dandy Dave]

Thinking that maybe crank case pressure may push some oil up the valve stems While the engine is running and may drip into the valve ports and lay there after it sits for a bit. Same with wet cylinders. The oil would collect at the lowest point of the pistons as they are on an angle. I would not be overly concerned and would drive it like you stole it. After all, It is a Cadillac and not one of them smoky old flathead fords with 35,000 miles on it. 😉 Dandy Dave!   

[Kurt Zimmerle]

Could it also be effected by the electric fuel pump that is set up running the car, that is by passing the  original vacuum system,  at a higher pressure then the vacuum system would provide?

[Dandy Dave]

6 hours ago, Kurt Zimmerle said:

Could it also be effected by the electric fuel pump that is set up running the car, that is by passing the  original vacuum system,  at a higher pressure then the vacuum system would provide?

That would be black smoke from gasoline. Oil would be gray smoke. Watch the color of the smoke and report back. Dandy Dave! 

[padgett]

Though oil was blue or is that only some ?

[JFranklin]

1 hour ago, padgett said:

Though oil was blue or is that only some ?

Grey/blue is oil, white is steam, black is TOO rich mixture.

Edited April 21, 2021 by JFranklin (see edit history)

[Kurt Zimmerle]

It was blue when it first started up, it did a little black when it was restarted after resting for a few minutes.  So the black sounds like its a fuel pump issue and I am learning there are ways where you turn off the gas pump first and let it run out as you stop so you would not get the black smoke. 

 

I hope to finish negotiations and do what Dandy Dave says "drive it like I stole it "  

 

Does anyone in this group have slightly used 7.00-21 tires I could buy to help drive my new baby home?

[C Carl]

Don’t buy it without a compression test. Also 7:00/21 tires are the size 1926 & 1927 Cadillacs use. Originally this car would have used 33x5. So it is running the later wheels. Doesn’t make much, if any, difference in this case. There has been a lot of time and money spent on the “interpretive restoration” of this car. But there is some reason it blows blue smoke on startup. Having spent 30 years lubricating the valves on my ‘24, I can’t see how oil could migrate to anywhere which could cause what is happening with this engine. Yes, you are a potential buyer, so the selling agent should provide at least a simple compression test which can be duplicated. There is absolutely no documentation whatsoever of any of the work which is said to have been done. There is objective evidence that whatever work, was not as complete as claimed. Compression tests are simple. And then there will still be some questions about bearing condition. But let’s see what the compression of all cylinders is first, and go from there. If any resistance to doing a compression test, (eg. “price as is where is” attitude, or whatever ), and if you would still like to make an offer, take 1/3 off the recent asking price to you and HOLD FIRM. What is that saying about a pig ? A pig in a poke ? What does that mean ? 
 

Let’s talk about further diagnostics. Paying a qualified mechanic to drop the pan and check the bearings - you have to do this anyway, either before or after buying it - would make sense. I have looked at , and bought and rejected quite a fair amount of Mercedes-Benz. Sometimes there is an enormous amount of documentation of service records. I have bought with confidence and been rewarded with an excellent car in all such cases. Without service records , you MUST have a good relationship with a known service advisor at the M-B dealer. Not just any dealer will do. If you do have access to such a dealer, you can pay for deep diagnostics. Pokey pig is not an option in the purchase of any complex, over engineered vehicle such as M-B. So here is how I do my thing. I write an agreement to purchase at a stated price, if the repairs at the M-B service center do not exceed x number of dollars. I deposit a down payment which I will forfeit if I do not purchase after finding repairs that do not exceed x dollars. No deal at the agreed price if repairs are more than x dollars. I have paid a few thousand dollars analyzing two different V12 biturbo ‘Benz. One quickly exceeded $20,000 in immediate necessities, the other was dismantled to the point where I was told that further dismantling might as well replace what was sure to be found needing work. I spent a lot of money to save a HUGE amount of money. Best bet for cars like these is to never buy one without complete service records from day one to the present. I have bought a magnificent 2001 S500, and a 2007 E550, (very good years for very good cars), with records. Bought with confidence, the S500 needed absolutely nothing, a truly superb luxury car. The rather high performance, (incredibly satisfying-my favorite driver of all time), E550 was only due for an inexpensive periodic service, and two free warranty upgrades. I have a lot of experience with M-B of this general period, and I recommend you structure some purchase agreement along the lines of what I have done. With the knowns and the sure-to-be unknowns , if your bearings are questionable, you might as well have Patrick Reeve rebuild the engine to his high standards for around $20,000. You may have this car for many decades, and many tens of thousands of miles.

 

Any comments on the possibility and desirability of a “subject to” purchase agreement ? You know : extraordinary claims require extraordinary proof. Or something like that.   -   Carl  
 

P.S. The black smoke is much more likely to be a carburetor issue than a fuel pump issue. You might be able to take your carb to Straight Eight personally for a very interesting visit. How close are you to Troy, MI ?

 

 

Edited April 21, 2021 by C Carl
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