A2 rough idle/firing miss

[Xloflyr]

I have an A2 with emissions that recently has developed several issues. On the first start of the day the engine will turn over pretty much normally than almost stop or ‘lockup’ momentarily before continuing to crank and then start.
The idle is poor with the engine is missing and making a ‘pfft pfft’ (?) noise at the exhaust tailpipe.
The valves have been set/checked per the TM, new coil, and internal elec in the distributor installed. Plugs all look the same indicating prob a rich condition. Plugs/cables checked and correct to the proper cylinder. This engine has a rebuilt carb and worked fine right out of the box for 800 miles since installation.
Another MUTT guy listened to this engine and thought he heard a slight odd noise coming from the timing cover area. Known engine issues include a leaking exhaust manifold in the center of the head. This has been present for a long time and up to now, hasn’t presented any problems other than an irritant noise when the engine is cold. Possible burned valve now?
I know this is pretty vague and there are a gazzilion possibilities as to wassup but any thoughts from other MUTT guys who might have experienced the same thing would be appreciated - thanks.

[m3a1]

I was helping him with this and would like to add that we removed the spark plugs, stepped on the clutch and pulled the engine through by the fan. It does seem to provide an unusual resistance during part of the pull-through which then eases for the rest of the 360 degrees but again, spark plugs removed.

Starter was straining to get the engine "over the hump" while turning the engine over. We charged both batteries which eased the problem somewhat. The problem seemed to ease somewhat after the engine had been running but was still noticeable.

We are going to pull a compression test and I hope, have a look at the motor oil/drain plug.

I'm not going to say what I think about this issue so as to get a fresh perspective . I hope some of the old hands will comment on this and maybe offer some suggestions as to how to go about narrowing this down.

Cheers,
M3A1

[rickf]

The only thing that will give a physical resistance on one cylinder while cranking with the plugs out would be a spun bearing binding up on the way around, a bent rod hitting the bottom of the cylinder or a ton of stuff on top of the piston. Stuff on the piston is pretty hard to believe if it was running not long ago, these are so low in compression you would be talking something like a mouse house to cause that. Now, if you had a blown head gasket and the cylinder filled with water and you cranked it over it could have hydrolocked and bent the rod or damaged the bearing. There is nothing under the timing cover that would cause that, it is only two gears. What he probably heard was the pump.
Have you pulled the valve cover to see if all the valves are working?

[m3a1]

Yup. All the valves are moving. No hydrolock as the plugs were out for this manual-pull-over iteration. Once the engine catches is seems to run fine other than that wonky intermittent miss. I am seeing evidence of a bit of exhaust gas escaping centrally on the manifold and he may be developing some valve issues there (we have yet to pull that compression test) so, that may be the cause of that stumble while at idle.

Frankly, I'm not entirely sure these problems are related.

While the engine is running I am hearing a persistent knock-knock with the same tonal quality as produced by knocking on the timing gear cover and it is definitely emanating from that area. The knock is not low, like a main bearing, but rather a knock with bit of a higher tone. Sound might be referred to that area through the block and is simply resonating off the cover. Camshaft bearing?

Water pump is reportedly new and I do want to loosen the belts and inspect the water pump by itself but I just don't see any evidence that the water pump is going to be at fault.

On the other hand, all these conditions might just be attributed to a timing gear that is no longer quite right on the cam-shaft which was all I could come up with.

Obviously, further inspection is necessary. Hopefully we'll get into it tomorrow.

Cheers,
TJ

[rickf]

The physical resistance and the knock are probably related, again, it may have hydrolocked in the past and bent a rod which is now touching the block. You are not going to know without opening up the bottom end.

[m3a1]

Well, we did everything but open up the bottom end. Simply cannot find any reason (at this point) why the engine is dragging. No debris in the oil, no issues whatever. The knocking sound I heard has quieted somewhat (in my opinion) but I finally went back home and started mine up and I am hearing a similar noise from my engine but mine is more like clockworks, all of which I attribute to the timing gears meshing. His engine really runs fine and has excellent compression so at this stage I guess I'm hearing hoof-beats and looking for Zebras when I should be thinking, Horses.

[KWIZ87]

I am chasing a similar issue in that my A2 has a intermittent miss and at times while driving it bogs down for bit but doesn't die. sounds like an exhuast leak to boot. However I have put new plug wires on, swiss controls and coil are fairly new, and new batts. checked PCV valve, good, Did a compression test and found that cylinder #3 and #4 are both low at around 75. #1 and #4 have good compression. I am in the process of re tightening the head bolts to check compression improvement. Re check the timing and then conduct a vacuum test to narrow down what is going on. I can see a lot of carbon build up on piston crowns and the plugs look uniform. Leaking head gasket? Keep you posted on what I find.

[rickf]

Sounds like a head gasket and since they are solid gaskets, not composition gaskets tightening usually will not work unless head bolts were loose and even then it will not work for long because the gasket has been burnt. Spray some carb cleaner around the intake manifold where it meats the head to check for leaks there. Be sure the intake hose is on the carb or you will get false readings. But with readings that low you will need to address that before you can resolve the running issue.

[m3a1]

xloflyr has good compression all across the board. I'm suggesting we do a vacuum test but some things have come up. We'll get a round tuit sooner or later.

[rickf]

We have two different threads going at once here and it is going to get very confusing. KWIZ87, I suggest you start a new thread with your issue and that way we can address yours without confusing it with someone else.