Advice for Troubleshooting an Odd-Fire V6 Engine with a Bent Pushrod

[GreyJose]

Hello fellow Jeepers.  I hope some one can help me decide my path forward on my 231 Oddfire.  I bought what I believe to be a 1970 Renegade I but it does not have the original Dauntless engine.  It has an oddfire distributor but the engine casting number are inconclusive, it could have been built as either odd or even fire in 1977.

The Jeep was back firing through the carburetor when starting and accelerating.  I started diagnosing the issue and found the following (condensed):

The 4 barrel Quadrajet carb use pretty dirty, all plugs except the #3 were heavily carbon fouled (pic) (#3 was a picture perfect example of a clean plug),  I confirmed that timing marks were reasonably close to TDC on #1, compression test on #1 was 120 psi, compression test on #3 0 psi, the intake valve on #3 was jammed open and not moving (at all), removed the rocker arm and #3 intake valve closed, the top of the push rod could barely be seen in the head (pic), using a magnet to extract it fell with a "tink", a borescope showed the top of the push rod about the same height as the lifter (pic),  pulled the intake manifold, found the push rod on top of the cam (pic) it was bent (pic), the #3 intake lifter has a section of the rim broken off and missing (pic).

I drained the oil with a magnet in the catch pan, found on eyelash sized sliver of metal and a pea size gob of dark oil on the magnet.  I will cut open the oil filter and drop the pan in the next couple of days to inspect them.

What should I do next?  Is that enough missing metal that it is time for a 100% tear down and rebuild?  Since I am 90% sure it is an original Renegade I should I give up on the Buick and try to find a 225 donor?  

Any and all advice will greatly appreciated at this point.  THANKS!!

[Moses Ludel]

Hi, GreyJose...I like your use of a borescope.  Look inside #3 cylinder for signs that the piston crown hit the open valve and also the condition of the cylinder wall with the piston at BDC.  Piston/valve interference will most often bend a valve.  Make sure that the valve, valve guide and guide seal are not damaged.  Be sure the valve moves freely.

If there is no obvious damage visible at this point, I would run a cylinder leakdown test on #3 cylinder with the piston at TDC and both valves closed.  (You might as well do this for each cylinder while you're at it.  There are reasonably priced leakdown testers available and worth having.)  If the engine passes a leakdown test (acceptable readings would be 20% maximum leak with each piston at TDC on its compression stroke, both valves closed), your immediate concern would be metal floating around in the engine and crankcase.

Use your borescope to peek inside the oil drain plug hole;  try to find the broken lifter piece.  It should be intact unless it slammed around in the crankcase or timing sprockets/chain.  If you need to drop the oil pan to find the lifter piece, you can also confirm whether the engine/crankshaft is an odd-fire with two connecting rods per crankshaft throw (three rod throws not six).  If you suspect that metal has run through the oil pump and everything else checks okay, install a new oil pump.  Pack the oil pump cavity with petroleum jelly to enable the engine to pick up oil prime.

Since you can see the valvetrain, rock the crankshaft back and forth to determine the amount of timing chain and sprocket wear.  The crankshaft movement before the camshaft sprocket moves indicates how loose the chain is.  A loose chain impacts valve timing.  If everything else in the engine checks okay, you can consider replacing a loose timing chain and sprockets with the engine in the chassis.  This would also verify valve timing at the same time, although you can test the valve timing with a degree wheel on the crankshaft pulley and measuring valve opening and closing events.

This work and testing are short of a teardown.  Your concerns would be compression/cylinder seal, valve timing, valve lift and bearing clearances plus oil pressure.  If the engine has reasonable leakdown percentages, correct valve timing, correct valve lift (camshaft and lifters okay) and good oil pressure without knocks, you can consider the engine road and trail worthy.  Of course 10%-12% leakdown would be optimal, but we're talking functional.  Oil consumption (valve seals, guides and ring seal) are each a consideration.

Once you confirm whether your engine is odd or even fire, make sure the ignition distributor matches the engine design!  Odd and even fire distributors and distributor caps are not interchangeable.  Confirm the right firing order, too.

From a tune standpoint, the engine and spark plugs indicate an over-rich mix as you note.  Make sure the choke functions correctly.  Explore the engine application (tag or stamping numbers) for the Quadrajet carburetor installed by the previous owner.  This may be way more fuel than needed or at least too rich jetting for the 231's needs.  "Factory" Quadrajet carburetors were used on some Buick even-fire 252 V6s, but they're rare.  Likely this is a V8 application carburetor and jetted too rich for your engine. 

Let us know how this goes!

Moses

[GreyJose]

Thank you so much Moses!  I believe it is mostly bad news regarding the inspection of #3 piston with the bore scope (3 pics attached). It looks like the piston has 450NP  .040 on it.   It sure looks to me like the piston was hit the intake valve.  There appears to be a fresh "scratch" on the top of the piston.  And then, there is that curly que looking thing in the picture, it almost looks like swarf from drilling or milling of metal.  I do not have a lot of experience using or looking at scope images so any and all interpretations are welcome and appreciated.  I have run a magnet around in there but nothing has come out.   My bore scope is a look forward kind of affair so I have only seen glances of the cylinder walls but what I could see showed very little wear with great cross hatching patterns.

Also included a picture of the broken lifter...that is a pretty big chunk(s) of some really hardened steel. I have pulled the pan and the biggest piece of the lifter I found was less than 0.1".  There was a magnetized lump of goop about the size of the tip of my little finger.  I flushed it off and found blasting media texture and sized metal.  

Thank you again for your guidance and help!

 

[Moses Ludel]

You're welcome, GreyJose...You learned a lot from the inspection of the #3 upper cylinder and dropping the oil pan.  The metal pan debris is not good...This engine was rebuilt with a 0.040" oversized bore, which indicates significant cylinder taper before rebuilding or a second rebuild.  Typical overhaul bore resize is 0.030" for most machine shops.  This is not a deal breaker unless reboring is necessary to repair block damage.  0.060" oversize is the practical limit and pushes the margins for cylinder wall thickness and cooling.  If reboring is necessary, I would do cylinder wall sonic tests if boring to 0.060" oversize.

The curled metal that you discovered and its proportional size rules out piston or piston ring material.  This could be just what you described:  Maybe someone resized or modified the Quadrajet spacer plate/adapter with the plate mounted on the manifold?  Drill shavings entered the cylinder through the intake port?  Other drilling was done like at the exhaust manifolds?  It's time for a complete engine teardown and parts inspection.

If you decide to use this 231 Odd-Fire V6 core, the complete teardown would determine what is salvageable.  You also have the bellhousing, motor mounts and other pieces to install an Even-Fire engine.  (Late '77-up rear wheel drive donor engines are readily available.)  I would consider the Even-Fire alternative.  You would need a complete donor engine.

The 225 or 231 Odd-Fire V6 is a rough running engine, balancing at a machine shop is tricky;  however, these engines are reliable.  (A Kaiser/Jeep engineer testing a V6 225 engine in a prototype CJ called the engine "...rough as a cob.")  An Even-Fire 231 V6 has many advantages.  I picked up a '78/'79 donor engine in the nineties for the CJ-5 featured in my Bentley Publishers book, the Jeep CJ Rebuilder's Manual: 1946-71.  The in-depth book features an engine section devoted to the Buick 231 V6 Even-Fire build that I did.

So this is where you're at in the process.  What are your plans and the intended use for the Jeep?  A Renegade is a classic CJ.  I recall combing over these forward-leaning models when they landed on the showroom floor.  Whatever path you plan, the result will be a very worthwhile Jeep 4x4.  I'd enjoy seeing pictures of your Jeep and details of its equipment!

Moses 

[GreyJose]

Hey Moses.  I unfortunately have reached the same conclusions about this engine.  The Renegade 1 was the first vehicle I absolutely fell in love with, I thought it was the coolest thing ever....and still do.  Since this engine is quite suspect in many regards I think I will try to find a 225 to keep the Jeep as close to original as I can.  "Grendel" will mostly be a pavement princess once complete, we'll do cruise nights and grocery runs with occasional trips to the mountains outside of Denver.  I was happy to discover it has a Warn overdrive, lots of gears to play with.

Thank you again for all of your help and wisdom.  By the way, I own very well used and loved copies of both of your Jeep books.  

Regards, Joe

 

[Moses Ludel]

Smart approach, GreyJose!  Your Renegade brings back a flood of memories.  This is a nice one to work with, too, very original plus the Warn overdrive.  The 225 option offers a spark of originality, the stock two-barrel Rochester carburetor actually works well if the donor engine stays original.  A Delco-Remy distributor is a must, the Prestolite is problematic and wear prone. 

Thanks for sharing these photos, and thanks for supporting my books!  You are at the perfect venue for the Jeep, it will be exciting to watch this project unfold!  Enjoy the process, I'm glad to comment when needed.

Moses