smart51
|
| posted on 2/11/06 at 09:27 PM |
|
|
What's wrong with my engine
It hasn't been right since it was refitted. Here are the symptoms.
It idles fine at 1000 RPM (normal) and 1500 RPM
It fast idle (2500 ish) it misfires a lot. The exhaust headers on the middle two cylinders glow (IR thermometer says 260°C) the outer two
don't glow and stay at about 200°C
Driving at low RPM (<5000) is fine at all throttle openings.
Driving at high RPM (<12000) is fine at a steady speed (small throttle opening)
Driving at high RPM at 1/2 throttle is slightly lumpy but not so bad)
Driving at high RPM at full throttle is bad. The engine hesitates then runs then hesitates again.
When the engine is hot, smoke comes out of the crank case vent. Not like steam from a kettle but with a bit of speed.
There dosen't seem to be a leak between the carbs and the block (squirts of WD40 don't affect engine speed.
There is good vacuum on the inlets and the vacuum holds when the engine stops.
compression is 115 - 150 PSI across the cylinders when hot and rises by 5 PSI with oil in the bores. The book says is should be 206 PSI. It was 140
ish when I first fitted it and has run just fine at that for a year.
The carb settings haven't been altered in many months. the problems suddeny occurred after refitting.
Any suggestions?
Edit, it doen't rev at 120000 at all!
[Edited on 2-11-2006 by smart51]
|
|
|
|
|
MikeRJ
|
| posted on 2/11/06 at 09:37 PM |
|
|
quote:
Originally posted by smart51
compression is 115 - 150 PSI across the cylinders when hot and rises by 5 PSI with oil in the bores.
Rule of thumb is no more than 10% variation accross cylinders so it sounds like there is a definate compression problem, which seems to be confirmed
by the excessive breathing.
Are the two cylinders that get hot the ones with lowest compression or is it fairly random?
|
|
|
Confused but excited.
|
| posted on 2/11/06 at 09:39 PM |
|
|
For what my two pen'th is worth, it sounds like the middle two cylinders are running weak. This would cause them to run hotter.
Running rough at the top end could be fuel starvation or an electrical breakdown in the ign circuit.
The loss of compression could be any number of factors. Valves not seating correctly, bore/rings worn, rings sticking in grooves, spark plugs not
tight, head gasket...... take your pick.
[Edited on 2/11/06 by Confused but excited.]
Tell them about the bent treacle edges!
|
|
|
smart51
|
| posted on 2/11/06 at 10:03 PM |
|
|
quote:
Originally posted by MikeRJ
Are the two cylinders that get hot the ones with lowest compression or is it fairly random?
The two hot cylinders, the two middle ones, have the best and worst compression.
|
|
|
yorkshire-engines
|
| posted on 2/11/06 at 10:28 PM |
|
|
Hi firstly why was engine taken out any work done on it?
sounds to me like either valve timing out or valve clearence too tight
give me a ring 07960011585
cheers malc
|
|
|
DIY Si
|
| posted on 2/11/06 at 10:29 PM |
|
|
It was removed to sort a problem with 2nd (?) gear, and since refitting has been hassle.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
|
|
|
smart51
|
| posted on 2/11/06 at 10:47 PM |
|
|
Yep. It jumped out of 2nd gear into neutral. The engine was fine before, though compression has always been a bit low.
When the engine came back, it wouldn't start because the compression was between 30 and 50 PSI in each cylinder. The engine went back to the
shop and they soaked it in WD40, getting compression back up. They blamed the piston rings.
The timing looked to be fine. They say they didn't touch it and it seems to be true.
[Edited on 2-11-2006 by smart51]
|
|
|
DIY Si
|
| posted on 2/11/06 at 10:50 PM |
|
|
Is there another shop you could get to have a look at it for you? Or are you anywhere near Malc/Yorkshire engines?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
|
|
|
Coose
|
| posted on 2/11/06 at 11:00 PM |
|
|
There are a few threads on it Malc - nothing above the gearbox was apparently touched!(?)
Four things could cause a significant rise in running temp: -
1, Too much ignition advance. Yours is of course a carb'd motor, thus cylinders 2&3 share a coil and an ignition pick-up. No Power Commander
is fitted. There is no way that the ignition could be advanced on cylinders 2&3 as the pickup is fixed to the same backplate as 1&4.
That's that ruled out!
2, Compression too high. You've checked that (numerous times) and all are actually below tolerance.
3, Tight piston-to-bore clearance. *If* this is your old motor, the top-end hasn't been touched so this should not be the case.
4, Cylinders 2&3 running lean. As the fuel enters the carbs between 2&3, there can't be a blockage within the carb fuel feed as the fuel
has to travel through 2&3 to get to 1&4.
Are the floats maybe sticking shut on 2&3? Is there muck in the float valves? Are the diaphragms ok? I'd whip your carbs off and have a
look, but I certainly wouldn;t drive it in anger until it sounds ok in the garage....
[Edited on 2/11/06 by Coose]
Spin 'er off Well...
|
|
|
Agriv8
|
| posted on 3/11/06 at 08:03 AM |
|
|
If you think its running lean on 2 of the 4.
would pulling the 4 into 1 exhaust and emissions testing each exhaust pipe. At tick over and fast idle.
Might be worth a look before pulling the engine to bits.
would reuire a freindly Mot atation with the old style gas analyser ( not one of the new ones that are being 'Watched ' by VOSA )
Just thinking out loud really.
regards
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
|
|
|
smart51
|
| posted on 3/11/06 at 08:13 AM |
|
|
Because 2 & 3 share an ingnition coil, and it is a wasted (shared) spark system, could a weak spark cause the above? The spark looks OK when
turning over. could it be swamped or something by fuel or pressure?
|
|
|
Coose
|
| posted on 3/11/06 at 08:40 AM |
|
|
quote:
Originally posted by smart51
Because 2 & 3 share an ingnition coil, and it is a wasted (shared) spark system, could a weak spark cause the above? The spark looks OK when
turning over. could it be swamped or something by fuel or pressure?
No, that would do the opposite as the mixture wouldn't burn properly, therefore the partially burnt fuel would cool those cylinders.
One thing to check - are the carb-balancing screws still fitted on 2&3? If you don't know, these are fitted to the head on the inlet tracts
just below the carbs. If these are missing it'll run lean.
Are you running the same plugs throughout all cylinders? If you're running a hotter grade plug in 2&3, that won't help. If
you're using NGK, the lower the number the hotter the plug.
Spin 'er off Well...
|
|
|
tks
|
| posted on 3/11/06 at 09:09 AM |
|
|
its
an problem on the 2&3 coil..
while connecting??
earthing of the coil??
conected wrong?? shorted??
somethng happened to that coil!
swap coils and check!!
Tks
The above comments are always meant to be from the above persons perspective.
|
|
|
02GF74
|
| posted on 3/11/06 at 09:30 AM |
|
|
I'd swap coils over and see if it makes any difference.
you wold expect the 2 central cylinders to be a bit hotter since they have a cylinder each side, t he ones on the end have only 1 - not sure how much
difference you can expect.
|
|
|
NS Dev
|
| posted on 3/11/06 at 09:39 AM |
|
|
The fundamental problem is the lack of compression. No decent engine will make much less than 150 psi when cranked over unless its built for forced
induction.
The car engines I have tested all made between 150 and 200 psi, without any oil in bores or other fiddling.
You need to find out what is the cause of this low compression before you can do much more.
Sorry to be the bearer of bad news, but it sounds like the compression was never great when the engine was "fine" before. With 140psi
compression it would have been down on power.
[Edited on 3/11/06 by NS Dev]
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
|
|
|
Coose
|
| posted on 3/11/06 at 02:59 PM |
|
|
The lack of compression wouldn't cause the exhaust manifold to glow though....
Have a look at the plugs - if they're white you're running lean.
If this is the case, have a look at the balancing screws as I mentioned previously. If they're ok, whip the carbs off and give them a good clean
up, checking that the floats aren't sticking shut.
It won't be a coil problem - the coils cannot cause the combustion temp to increase. Decrease, yes (causing a poor spark) but not increase.
What fuel are you using and where did you buy it? A lower octane fuel than normal will burn hotter and cause poor running. If you filled it up at a
supermarket I'd drain it and get something decent in there - you won't need Super unleaded, just something decent.
Regarding your overall lack of compression, this winter may be the time for a re-ring and lapping in of the valves....
Spin 'er off Well...
|
|
|
ChrisGamlin
|
| posted on 3/11/06 at 10:44 PM |
|
|
Considering the compression check from when the engine ran OK was still only around 150psi, I wouldnt be suprised if the gauge being used is
inaccurate, which in turn is leading to a mis diagnosis.
Having said that, it does seem rather odd that there was virtually no compression after the rebuild. If the top end really wasnt touched by the
workshop then there's no reason it should have done that, it wasnt standing around that long was it? As Coose alluded to, you have definitely
got YOUR old engine back have you?
|
|
|
MikeRJ
|
| posted on 3/11/06 at 11:08 PM |
|
|
quote:
Originally posted by Coose
The lack of compression wouldn't cause the exhaust manifold to glow though....
It is possible, low compression will cause a slower burn, which is why low compression engines require more igntion advance. However, the cylinders
most down on compression and the glowing headers don't match up it seems.
|
|
|
smart51
|
| posted on 5/11/06 at 09:06 PM |
|
|
I've just run a little test, after being away for the weekend. I swapped the coils / HT leads / plug connectors from 2 & 3 ( the hot ones)
with 1 and 4. When run at 2500, all 4 exhaust headers glow red. When put back to normal just the inner two glow.
I stopped the engine instantly and checked the plugs. They're exactly like the "all is OK" picture in haynes. Whilst I was at it I
measured the resistances of the coils and plug connectors. All is within spec, although the coil primary winding are right at the top of the spec.
I balanced the carbs before SVA last year. That's not to say they're still correct. I'll check.
The fuel I bought from a "brand name" filling station. Can't remember whose.
The compression gauge is a cheap one - the only one I could find with a 10mm thread. With the volume in the tube + guage added the the volume of the
cylinder, it could read a bit low, especially with the small cylinders of a 1000cc engine.
So, swapping the coils makes the cool exhausts hot but not the hot ones cool. Is this a red herring or part of the problem?
|
|
|
NS Dev
|
| posted on 6/11/06 at 08:09 AM |
|
|
we had a persistent misfire that only manifested itself after 15 to 20 minutes racing on the Radical this year, using a Hayabusa 1500 with carbs and
Dyna (IIRC ) coils.
We also had the " 2 cyls cooler" issue but it was not the two with the failing coil strangely.
I told the team that the only time I had ever found a misfire that only happened when everything was really hot it was always coil related. They
chased everything up, but eventually, it was the coil breaking down at high temp.
Still doesn't explain the compression, but maybe the cheap gauge is causing that, but then why did it drop so much after going into the
workshop.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
|
|
|
smart51
|
| posted on 6/11/06 at 10:36 PM |
|
|
I've tried a couple of things based on suggestions.
The timing rotor on the end of the crank does line up with the No 1 piston at TDC so it hasnt rotated on the shaft.
Running the engine in the dark doesn't show up any stray sparks, when cold or hot.
The carbs are balanced quite well.
Why is it everything I try is the same as it was when the engine was working?
|
|
|
t.j.
|
| posted on 7/11/06 at 08:29 PM |
|
|
Can you measure up your mixture in all the cilinders apart?
I think the 2nd and 3th are getting a too lean air/fuel mixture.
this could causes the temp. rise.
|
|
|
smart51
|
| posted on 7/11/06 at 10:31 PM |
|
|
quote:
Originally posted by t.j.
Can you measure up your mixture in all the cilinders apart?
I think the 2nd and 3th are getting a too lean air/fuel mixture.
this could causes the temp. rise.
I don't have a way of measureing the mixture. Just seat of the pants and spark plug colour.
|
|
|
smart51
|
| posted on 8/11/06 at 08:19 AM |
|
|
I took the head off yesterday. The gasket is just fine. The head and block are flat. I poured solvent into the ports and none leaks past the
valves. I poured oil into the bores and it is still there this morning. It looks like there are no leaks. It must either be fueling or spark.
|
|
|
