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Help - One cylinder running hotter than the others?
dhutch - 5/12/13 at 11:46 AM

The rear cylinder on the westfield has recently started running hotter than the others, certainly with the bonnet off when your looking at it its a dull/mid cherry where the others are basically black.

The engine is a 1.9 CVH (based on a 1600 block and head) on twin dellorto dhla 40's, tubular 4-2-1 manifold, ignition from a megajolt unit.

My thoughts are
- Has something happened to a jet in that barrel.
- Is it just at idle, or does the issue remain when driving.
- Will it be doing any significant damage to the engine running like that.
- If put half a turn on a get of choice to make it richer....? Which jet? in or out....
- Can I drive it an hour to my girlfriends and back tonight?

Currently the tin-top is off the road and it has become my only car, so an 'instant fix' of some sort if only for this evening and the next week would be ideal.

Previously to me noticing this the throttle return arm and felt/leather washer has come off that end of the spindle, but that washer isn't the seal for the air in anyway so as far as I know should not effect it, there is also a fair crack in the manifold at the 4-2 join but while far from ideal and might increase the burning of fuel in the exhaust, I cant see that overly effecting the primary right up to the head.



Daniel

adithorp - 5/12/13 at 11:59 AM

Could be air leak on that inlet (gasket or manifold) or fueling on that carb barrel causing weak mixture so running hotter.

Exhaust valve on that cylinder not sealing or cracked could cause it. You'd normally feel a missfire but maybe not. Try a compresion test.

Is this at idle? That would surprise me.

dhutch - 5/12/13 at 12:08 PM

quote:
Originally posted by adithorp
Could be air leak on that inlet (gasket or manifold) or fueling on that carb barrel causing weak mixture so running hotter.

Exhaust valve on that cylinder not sealing or cracked could cause it. You'd normally feel a missfire but maybe not. Try a compresion test.

Is this at idle? That would surprise me.

Its a fairly fast idle, 1200rpm maybe? It pops and crackles a bit but I have not noticed any worse a miss-fire since its developed. I'll check for leaks between the carb/manifold/inlet at that end I guess.


Daniel

britishtrident - 5/12/13 at 12:40 PM

Exhaust valve burnt out or not sealing due insufficient tappet clearance.
A compression test or cylinder leak-down test will confirm.

dhutch - 10/12/13 at 03:26 PM

Compression tester is due into day or tomorrows post.

Not had any time to look at this yet, and have secured the use of another car for a while but will update again!


Daniel

dhutch - 12/12/13 at 11:01 AM

quote:
Originally posted by dhutch
Compression tester is due into day or tomorrows post.

Did the test.

Effected cylinder (no4) blow a heathy 155/150 as did cylinder 3.

The presures then dropped right off 120, 100 as the race battery wasnt upto any more in the cold, but with a much larger but not fully charged battery lash along side i got a consistant 120-130 over all four.

So its not burnt an exhaust valve atleast.... back to the drawing board on that.

Not done anything with the carbs in five year since a clean down when I bought the car, so might look at that next.


Daniel

garyo - 12/12/13 at 12:01 PM

Swap the carbs over to see if it moves? In doing so you may well disturb the o-rings and fix the problem anyway...

Second thoughts, you'll then have messed about with your balance screws between the two carbs, so maybe not if you want it for the weekend.

dhutch - 12/12/13 at 01:01 PM

quote:
Originally posted by garyo
Swap the carbs over to see if it moves? In doing so you may well disturb the o-rings and fix the problem anyway...

Second thoughts, you'll then have messed about with your balance screws between the two carbs, so maybe not if you want it for the weekend.

Moving the carbs is not a stupid idea, nor is simply taking them off and putting them back on again.

The between-carbs balance screw was adjusted by eye (and ear) when the carbs where refited last time so not a huge loss.

First this im going to do it just put the plugs back in and see if it still persists. I have then had a suggestion to spray water around the inlet o-rings while its running and listen is there is a change in engine note whichy apprently can work to indicate a leak.

On the topic of the plugs, all looked about the same. I can add a photo when I get home, but there were all matching and looked find, if a tiny bit sooty. They must be two year sold now.
Looking at the below image, somewhere between third from the left on the top row, and third from the top on the right row. http://motogymkhana.pl/katana/wp-content/uploads/2013/04/spark-plugs-guide.jpg


Daniel

coyoteboy - 12/12/13 at 05:44 PM

Leaner mix doesn't burn hotter than stoic, peak energy output is at stoic. Running leaner runs cooler (because for any given cylinder volume you have less energy total to burn) and running richer runs cooler (because the additional fuel has a cooling effect on top of the total burn). But running leaner slows combustion to the point where it continues burning out of the exhaust valve on a normally timed engine.

I'd be looking for a reason for one cyl to run significantly lean such as blocked jet or leaky gasket, and I'd be checking tappet clearance when at operating temp.

dhutch - 12/12/13 at 06:40 PM

Could change when it get hot, but its on hydro tappets, so it should all be under control?

Leaning towards a gasket or a blocked get myself.


Plug photos:
http://imageshack.us/a/img17/3329/cwnq.jpg
http://imageshack.us/a/img543/8760/vvb5.jpg


Daniel