persistant miss fire

[dubby]

Single port engine miss fireing on number 2 after overheating ( not seized )
Changed :-
plugs
points
disributor
coil
carb
pistons & barrells
leads
commpression test is fine and have lapped in valves while head was off
we have fuel mix, commpression & spark in that pot,,, but no bang!
Any ideas?, will take engine out again tomorrow and change head and valve gear,, just cos its the only thing we havnt yet changed !!!
The push rods have been swapped around yet the problem remains in number 2
Dubby

 

[ronmidg]

looking at what you've changed there's not much else to point at, maybe the overheat distorted something, a gap at the manifold?

 

[noddy]

If the head has warped you could be drawing air though the gap between the head and barrel instead of through the manifold so no fuel to ignite.

If head is warped you can usual hear a squeak on start up as gas escapes through the gap.

If the head has warped you can lap the barrels into the head to cure it, but you will need to do both barrels, or if you have an old barrel use this to save taking the barrels off the block.

Apart from that I would guess you have a really lean mixture going to that piston due to leaks else where.
Valves opening and closing ok on this cylinder?

 

[dubby]

Cheers guys, I sort of guess it points at the head / valves simply because its the only original link in the chain now. There is nothing visible as it been off & inspected a couple of times now. Hopefully I will be able to get a replacement unit today and try that.
Dubby

 

[dubby]

Now where do I look ?, swapped the heads across so that 1,2 is now 3,4 and vica versa and still missing on 2 !!!!, set tappetts, changed distibutor and all ancilliaries again, replaced crush ring in single port manifold and tested with WD40 when the engine was running to see if it would draw any in. Spoke with an auto electrician, he said it cant be coil ( though have tried another. the plugs and leads have been swapped around again & I can see a fat spark when I try number 2 outside the cylinder.
I think I have tried all mechanical elements ( except a camshaft ) & all electrical, does anyone know of a fuel problem that can effect No 2 on a sigle port engine?
Dubby

 

[Araon]

You didnt draw out the push rods and have a gander at them did you whilst you had the heads off, not running a worn/bent rod, dizzy cap contactors in good order

 

[noddy]

I know its a long shot but is there a chance that anything like a rag could be left in the intake?

It has to be a fueling fault at that cylinder so the only thing that comes to mind is that the intake valve is not opening for some reason, could be either pushrod as previously pointed out, cam follower or the cam lobe for that intake valve is badly worn, or push rod not seated fully when valves adjusted.

Do you push the back of the valve rocker down onto the push rod when you adjust your valves to make sure the gap is correctly adjusted?

If it were me I would take the rocker cover off take the plugs out and get someone to crank it over and check that the valves are opening and closing on that cylinder.

 

[dubby]

Cheers, dont think it can be anything in the manifold as my son jetted it with the airline, & as its a single port it should also affect the number one cyl. now that the heads have been swapped across it sort of eliminats rocker gear as that went with the heads, & push rods have been swapped around, the thought of a cam is scary but I suppose its possible as we would still get a good commpression reading, will try checking the action with the rocker off, although valves all seemed to be moving OK when I was adjusting them and my son was turning the engine over manually.
I havnt been pushing the rocker arm down when adjusting, but I have set them 3 times now, and its just number 2 that plays up.
Cheers Dubby

 

[noddy]

The only other thing I can think of is the plug is not earthing when its in the head so no spark when fitted.

Does this problem clear up when the van is revved?

What carb and dissy are you running what have you got your timing set to?

 

[dubby]

Hi, dont have a strobe, so just setting the timing manually using a test light by backing off TDC untill points just opening ( as per Haynes manual ),,, should be alright for static timing,,, dizzy is the vacuum advance type, have tried 3 now, one is back in its owners vehicle and is fine, carb I think is a 32 pict solex.
Engine does sound fine at start up ( choke will be on ) also sounds fine through rev range but back to tick over it misses,,, plugs are all sooty but we not running it for long.
Is it possible for a plug not to earth when fitted ?
could mixture effect number 2 rather than all cylinders ?

 

[noddy]

Have read some where not to use lubricant or anti seize compounds on plug threads, as it can cause plug not to earth.

As for sooty plug that would indicate rich tick over mixture. Base setting for the tick over screws is fuel screw from fully in (lightly seated dont jam it home) back out 2.5 to 2.75 turns, then start engine let it warm up and set tick over using air screw to about 850 rpm +/- 50 rpm.

If you could time it with a strobe it would be better that a static setting.

The only other thing I would try is opening up the plug gaps to 0.7mm, I never leave my with the 0.6mm setting they are supplied with.

I have had the same problem with my single port but it seem to come down to having every thing set spot on timing, carb tick over mixture etc.

 

[dubby]

nothing on any of the plugs and have swapped the plugs around the cylinders, I cant find anyone who knows if rich mixture would just effect one cylinder. am going to try measurung rocker movement tomorrow to establish if camshaft has worn lobe,,,, as much as I want to find the problem Im really hoping its not the cam !
Haynes manual said .7mm for plug gaps , so thats what they set at, thanks for the tip on mixture setting,,, did you have a missfire similar ?
Dubby

 

[noddy]

Similar but not persistent, just went through the whole tune up process, including stripping and rebuilding the carb.

Dont seem to get the problem anymore, I would try to get the timing spot on, if its a single vac advance dissy (the one with the large flat vac unit) you will need to time it for 0 degrees ie tcd on no 1.

 

[dubby]

Cheers, have booked a client of mine who is a mechanic by profession, ( has all the equipment on his van ) to meet me at the car tomorrow to tune it properly and run any tests I havnt, he mentioned vacuum testing the inlet manifold .
Will let you know what we find
Brean Sands camping is a possibility next weekend, and Vanwest is there this year I just found out.
Dubby

 

[dubby]

Mechanic set timing using strobe and set carb, sounded sweet, but it still wont run on all four! noticed spark arcing from pos on coil to centre HT. auto lec and VW guy say this isnt the problem, but it is a symptom of a problem as the spark only jumps when its an easier route than the one its supposed to take.
Have limped the car to Aircooled specialist,,, im beat.
Fantastic weekend at "cruise to the prom" at Weston Super Mare, missed the start at Brean due to road closure at Glastonbury but met up at beach, great company, great vans and cars, great weather.

 

[dubby]

Its fixed !!! At some point in my swapping around I introduced a faulty HT lead from a second set,, because I believed that I was irradicating the problem by bypassing the first set I looked elsewhere!, we have now changed so much that I have no idea what the first problem was !!!
The car storms along, didnt want to push it but it did 75mph and was still pulling so it will be interesting when its settled in.
A friend has now bought a 2ltr v reg camper with a hoted up engine with twin Delartos,,,, and it sounds like big end is shot, usuall story spent all her money buying the van, do you know if a 1600 will go straight in?, a turnkey is likely to be quicker & cheaper than stripping the 2ltr, & I have never done anything on the 2ltr so its new territory.
Dubby

 

[noddy]

Glad to hear you got it sorted.