Flathead V-8 Rough Running (popping sound)

[csearider]

After reinstalling a rebuilt 322 flathead in my '40 LaSalle, I cannot get it to run smoothly. There is a distinct miss that sounds like a popping sound in the exhaust and engine runs roughly.

The particulars of engine rebuild was a complete machine overhaul by qualified shop with many years on flatheads. Machine work included complete valve job, crank ground on mains to .10 over (standard bearings were not available), and bored out for new 346 pistons. Rings, bearings, timing gears and cam gears with new chain as with everything else was new parts or rebuilt. Cam and crank gears were set to specs in 1940 Cadillac shop manual. Compression is 110-115 lbs all cylinders.

Distributor and wiring were set per 1941 Cadillac Shop Manual per diagram see attached.

I set distributor to #1 per diagram @ TDC and and first installed distributor where #1 sat at about 11:50 to firewall (where #2 seen in dia) looking from front of vehicle. Timing mark was at / on the IG/A. Could not get vehicle to run smoothly and no change in engine rpm when wires removed from cylinders #3 + #5 left bank and #4 on right bank (from driver position). I thought maybe I was a tooth off so reset distributor to where #1 was more at 11:55 as seen in diagram to firewall and popping seemed to decrease, but was still there.

I have installed 2 different sets of points/condenser thinking maybe bad and set latest to .16. A second cap and rotor have been ordered. Wires are new and have spark to all cylinders.

Popping or the miss is not thru carburetor so not readily apparent due to a valve problem, but lying at right front door on ground it can distinctly be heard in exhaust.

Timing was adjusted with vacuum to distributor disconnected and was slightly advanced (before mark)... retarding timing slightly did not help.

I believe I have done everything correctly and in dire need of help on this one. Can anyone with hands-on knowledge with a 322 flathead give me some advice??? I do understand that the timing can be difficult on these engines.

The local chapter of AACA will take on the wiring of a complete vehicle harness after the beginning of the year as a club project on Saturdays (if anyone needs to know why it is important to belong to a car club that is a prime example!)I need this solved before the club begins the project. This is kinda embarrassing to tell the truth!..as well as frustrating with the new rebuild process.

[Steve Passmore]

Remember to check that you have the ign set to the correct TDC,   There are of coarse two positions, number one cylinder will have a TDC on its exhaust stroke too, it must be set on the compression stoke.    Just an obvious thing but so often overlooked.
Next follow every plug lead from the distributor to each plug and make sure they correspond with the firing order clockwise in the distributor.

[Bob Schuman]

After the valves on a flathead are ground and seats refaced, it is essential that the cam heel to valve stem clearance of each valve be measured. It must be 3.000 inches, within about +-0.010 inches, to allow the hydraulic valve lifters to operate within their limits of travel. If the 3 inch dimension is much below 3 inches for any valve, it probably will not allow that valve to close completely while running. When checking compression the engine is turning much more slowly, allowing the valve lifters more time to "bleed down" and not hold any valves open. The clearance is adjusted by grinding the valve stem to the proper length. This should be a last resort item, because it requires removing the intake manifold, lifter covers, and the lifter blocks for access, and if any clearances are below about 2.990, the head or heads and offending valves must be removed to shorten them.

I hope you are able to find a cause for your miss that is much easier to fix.
Bob Schuman,CLC#254

[csearider]

WOW!!!!!! excellent input, I will need to check with my machinist Monday...no sleep this weekend!
Hopefully, someone else will make a suggestion that will negate having to go this way....Need Help club members!!!!!!!

Bob,
I gave machinist all the shop manuals and spec books before starting.....is this detail explained in the manuals or is it just something a good machinist knows to do? Also, is it practical to run a compression check on a running engine...never done so, has anyone any experience on this???

I have also heard to set timing >+>+>+>advanced and set vacuum to highest level at least 19-20....

[Steve Passmore]

[quote

Bob,
I gave machinist all the shop manuals and spec books before starting.....is this detail explained in the manuals or is it just something a good machinist knows to do?
[/quote]

What Bob has said is absolutely correct and it is in the manual but I have seen this overlooked many times. The valve seats on these engines are supposed to have three different angles but even a machine shop doing an engine for me in the 90s completely ignored this and cut a deep single angle seat never checking the 3" clearance even though they said they did. the complete end of the valve would have had to be ground off including all the keeper groves rendering the block useless or it would need new seats fitted.
Check the other fundamental things I've suggested first.

[Jeff Hansen]

If you get to the point where you have to open up the engine to get at the lifters, take the time to ensure all of the valve spring components are in place for each valve. To do this, once you have a lifter block out, use your thumb and press up HARD on each valve stem in an attempt to open the valve.  If you are able to open any valve in this fashion, there is a spring seat missing on that valve.  A missing seat will show up as a miss especially if the missing seat is on an exhaust valve.  I can speak from experience on this...

Jeff

[csearider]

Seems like there should be a method to test cylinder pressure before opening up the engine. I have heard of but have no experience with what I hear referred to as a Dynamic Compression Test.......this test tests cylinder pressure with engine running...anyone have knowledge or experience with same?

[TJ Hopland]

I think dynamic compression is more of a theoretical calculation rather than an actual test.   It takes into account things like valve timing and how things flow under operating conditions.  That is one way they get more performance out of engines like the Northstar and other newer designs.  They change the cam / valve timing to change the way the engine behaves.  When they make that change they also change the air fuel ratios and ignition timing to get the desired results, it all has to work together to work at all.

I like the valve theory.  An exhaust valve not closing as it should would leave the dynamic compression weak in that cylinder which means if it did fire it would not be complete combustion so you would get a lot of unburnt fuel into the exhaust which then could be ignited by the heat and fuel from the other cylinders giving you the pop.  This also give you the roughness because that cylinder is not doing its share of the work.  If it was an intake valve it would likely run a lot worse and pop in the carb from time to time.   

[Two Crabs]

I broke one of the 10 mm spark plugs and made a fiitting from it for my compression gauge. I could no find any reduces from american threads to the 10 mm thread.

[csearider]

Carquest supplied me a reducer for their compression gauge....inexpensive and works great!

[R-body_mopar]

If you get to the point where you have to open up the engine to get at the lifters, take the time to ensure all of the valve spring components are in place for each valve. To do this, once you have a lifter block out, use your thumb and press up HARD on each valve stem in an attempt to open the valve.  If you are able to open any valve in this fashion, there is a spring seat missing on that valve.  A missing seat will show up as a miss especially if the missing seat is on an exhaust valve.  I can speak from experience on this...

Jeff

I have heard of this happening before on engine rebuilds; the valve spring seats are stuck in the block, but can come out in the cleaning process!  This is not easily noticeable when re-assembling the engine, but the valve spring pressure will not be sufficient to close the valve completely when running.     

In fact, Jeff Hansen probably posted this before about his experiences..... That's probably where I read it in the Self Starter!   

[Jeff Hansen]

I have heard of this happening before on engine rebuilds; the valve spring seats are stuck in the block, but can come out in the cleaning process!  This is not easily noticeable when re-assembling the engine, but the valve spring pressure will not be sufficient to close the valve completely when running.     

In fact, Jeff Hansen probably posted this before about his experiences..... That's probably where I read it in the Self Starter!   

Doug Houston first wrote about the valve spring seat problem in The Self-Starter back in the late 60's.  The engine he and his friends were working on was missing 14 of the 16 upper spring seats!  That's where I got the idea to check for that situation on my engine. 

Here is a link to a post I made some time ago with a PDF of Doug's article attached:  http://forums.cadillaclasalleclub.org/index.php?topic=104950.msg135750#msg135750

Jeff

[R-body_mopar]

Thanks, Jeff........I knew I had read that someplace, but I just didn't think it was that long ago!

I'm gettin' old......but my memory still works....I think!

[Tom Boehm]

The hint about the valve seats getting lost is also in the 1939-1940 Lasalle authenticity manual in appendix H.

[Flathead16]

If all else fails,and I might add all bases should be covered by other members already, you should check your oil pressure. If it is too high you could be lifting the exhaust valves. Use a 5-20 oil heavier oils should be avoided.
  Steve Loechner

[csearider]

Problem has been solved!
The major problem was the location of #1 TDC on ignition wires to distributor as seen in '41 Workshop manual diagram fig. 29 on pg. 39. The dia. shows #1 almost at the 11:55 position to firewall, however it needs to be set to the position as seen in dia left of the back distributor clip (2 connects over from clip) which puts it more at 11:50-55 on my vehicle to firewall to set timing correctly otherwise it was 1 tooth off. However, although this helped there were several other items of which one was not the only culprit as follows:
1. Removed barely used Champion plugs and replaced with AC plugs ( A mechanic with vast electrical experience with the Flathead suggested this)
2. Replaced barely used Distributor cap with new BWD C12 from Advance and it had better fit than previous one snapped into place as previous one was always suspect
3. Also a new BWD rotor D80
4. Removed distributor entirely from vehicle blew it out and cleaned it, replaced frayed wire from points to housing ( a short here was likely) and set points out of vehicle to .016 (points were very difficult to set properly without them moving slightly when adjustment screw was tightened but after several tries it was good)
5. Set choke cold @ width of 1/64# drill bit
6. Readjusted carb settings

I think it was a combo of all the above not any single item. It should be noted that before I would have gone down the road related to valve problems I would have done a vaccum test at manifold and if necessary a running compression test.

Hope this helps.