compression test
Discussion
A few weeks ago I posted a topic about my 1993 esprit SE boosting at 4+ psi to hold a steady 80 mph. I have just done a compression check and found all four cylinders to be exactly 120 psi. I was wondering if anybody out there knows what the figure should be (I realise that different gauges will give slightly different readings). I consider this to be a little low. I also checked the inlet manifold vacuum - about 12 inches of mercury which is also low and possibly goes some way to explaining the boost levels I am getting. The car has covered 55000 miles with full lotus history. It has just had a cam belt change and tappet reset, so my next thing to look at could possibly be valve timing (even though you would expect a main dealer not to get this wrong!) Anybody got any suggestions on the compression levels or thinks I am wasting my time looking at the valve timing? Any suggestions would be welcome. The car runs and performs extremely well, doesn' t use any oil at all and doesn't puff any smoke at all no matter how hard you rev it (so I don' t think I have a problem with rings / bore wear ).
A few weeks ago I posted a topic about my 1993 esprit SE boosting at 4+ psi to hold a steady 80 mph. I have just done a compression check and found all four cylinders to be exactly 120 psi. I was wondering if anybody out there knows what the figure should be (I realise that different gauges will give slightly different readings). I consider this to be a little low. I also checked the inlet manifold vacuum - about 12 inches of mercury which is also low and possibly goes some way to explaining the boost levels I am getting. The car has covered 55000 miles with full lotus history. It has just had a cam belt change and tappet reset, so my next thing to look at could possibly be valve timing (even though you would expect a main dealer not to get this wrong!) Anybody got any suggestions on the compression levels or thinks I am wasting my time looking at the valve timing? Any suggestions would be welcome. The car runs and performs extremely well, doesn' t use any oil at all and doesn't puff any smoke at all no matter how hard you rev it (so I don' t think I have a problem with rings / bore wear ).
Dan,
I suspect that you may have a problem with the compression test you performed. The cpmpression readings should be 170-190PSI. The fact that all your readings were unchanged at 120PSI leads me to believe that the test was improper.
Was the engine warm? Were all the plugs removed? Was the throttle wide open throughout the test? Did you rotate the engine a minimum of 4 rotations on each cylinder? If your answer is not yes to each of these questions, your test was improper and must be checked again. Any of these things being wrong could also explain your low vacuum readings. Hope this helps...Jim '85TE
I can say yes to all the questions you asked. I have carried out the procedure several times before, but not on this car. Thanks for the suggestions all the same and thanks for the figures. The fact that the figures are all the same across all four cylinders gives me some confidence, although they are all low.
danny tattersall said: I can say yes to all the questions you asked. I have carried out the procedure several times before, but not on this car. Thanks for the suggestions all the same and thanks for the figures. The fact that the figures are all the same across all four cylinders gives me some confidence, although they are all low.
Dan,
I agree that consistency is the thing. Was the engine ever rebuilt? If not, I guess wear could account for the low readings, but I still suspect something's not correct. I'll do some research and get back to you. Happy Motoring...Jim '85TE
1. Did you add a few drops of oil into the cylinder to see if it changes the compression
2. Check your oil.. any coolant in there?
3. Boost leak? Make sure all your gaskets are in place and intact.
If you blew rings or head gasket you would most likely see some smoke under boost. You should also perform a leakdown test.
2. Check your oil.. any coolant in there?
3. Boost leak? Make sure all your gaskets are in place and intact.
If you blew rings or head gasket you would most likely see some smoke under boost. You should also perform a leakdown test.
Thanks greezmonkey. I have not yet added oil to the cylinders, but I will do so just to rule out the bottom end of the engine being worn. The head gasket is fine so there is no oil in the water or vice versa. I have had a leak down test done on a previous car and it is the best way to assess where the pressure is being lost, but I wanted to exhaust the things that I can check before going to the garage. Thanks for the assistance anyway, you are thinking along the same lines as me but I am still hoping it is the valve timing. I have not checked this yet because I do not know what the alignment marks on the cams line up with and what the crankshaft lines up with. If you know where they are I would appreciate it if you could let me know before I start crawling underneath the car!!!!!
I read the original post and have a few thoughts.
1. My S4s at 80mph is right on the edge of showing positive boost. A slight incline or a headwind will do it. Honestly, I don't see how this is a problem. The car needs X hp to move forward and (IIRC) a little positive pressure is actually a slightly *more* efficient way to get that X hp. If you're seeing more boost than before, I think it's a symptom, not the problem.
2. I think your compression numbers are probably OK as they're so even. My car was 130 across the board last time it was checked. Is the gauge accurate? Who knows?
3. The mileage issue is the only one that jumps out at me. I see about 20 in mixed hwy/city but 25+ on long constant speed trips.
How old is the O2 sensor?
Have you made any changes to the exhaust?
1. My S4s at 80mph is right on the edge of showing positive boost. A slight incline or a headwind will do it. Honestly, I don't see how this is a problem. The car needs X hp to move forward and (IIRC) a little positive pressure is actually a slightly *more* efficient way to get that X hp. If you're seeing more boost than before, I think it's a symptom, not the problem.
2. I think your compression numbers are probably OK as they're so even. My car was 130 across the board last time it was checked. Is the gauge accurate? Who knows?
3. The mileage issue is the only one that jumps out at me. I see about 20 in mixed hwy/city but 25+ on long constant speed trips.
How old is the O2 sensor?
Have you made any changes to the exhaust?
danny tattersall said: Thanks greezmonkey. I have not yet added oil to the cylinders, but I will do so just to rule out the bottom end of the engine being worn. The head gasket is fine so there is no oil in the water or vice versa. I have had a leak down test done on a previous car and it is the best way to assess where the pressure is being lost, but I wanted to exhaust the things that I can check before going to the garage. Thanks for the assistance anyway, you are thinking along the same lines as me but I am still hoping it is the valve timing. I have not checked this yet because I do not know what the alignment marks on the cams line up with and what the crankshaft lines up with. If you know where they are I would appreciate it if you could let me know before I start crawling underneath the car!!!!!
Danny,
I had no idea that you hadn't verified the valve timing. That's a whole new 'kettle o' fish'!
To confirm your valve timing, the 'dot' on the rim of each camshaft timing pulley will directly line up when the engine reaches TDC (This can be checked by either seeking the TDC mark on the crank pulley, or by peering down at the flywheel and looking for the timing pointer. The flywheel is marked in 5° increments. You can align the timing marks easily by pushing the car in 5th gear with the plugs loosened. If your garage is not deep enough to push the car all the way to alignment, put the car in neutral and push it back, re-engage 5th gear and push it forward again.
It goes without saying that if your timing is off, both compression and vacuum will be effected. It is not unusual for a timing belt to jump a tooth and the jump of a single tooth will only have the effect of making the engine seem sluggish or poor idling. Let me know what you find. Happy Motoring...Jim '85TE
Although Jim is usually correct, on figures relating to Esprit's the figure of 170-190 lbs while correct for a carb turbo is incorrect for an SE. The correct readings for 89-93 SE is 140 lbs. minimum (usually a little higher). So 120 is not that far off. I do think there has been an error in conducting the test. Could be the throttle plates were not open all the way. When cranking the engine did you press the acellerator pedal? Sometimes this throttle cable is not set correctly not allowing full throttle opening. Crank open the throttle plate from the engine and remove all plugs during the test. Allow the engine to crank for a while on each cyl. you test.
Good Luck,
Calvin
Good Luck,
Calvin
cnh1990 said: Although Jim is usually correct, on figures relating to Esprit's the figure of 170-190 lbs while correct for a carb turbo is incorrect for an SE. The correct readings for 89-93 SE is 140 lbs. minimum (usually a little higher). So 120 is not that far off. I do think there has been an error in conducting the test. Could be the throttle plates were not open all the way. When cranking the engine did you press the acellerator pedal? Sometimes this throttle cable is not set correctly not allowing full throttle opening. Crank open the throttle plate from the engine and remove all plugs during the test. Allow the engine to crank for a while on each cyl. you test.
Good Luck,
Calvin
Calvin,
Good call on the maladjusted throttle cable! A common fault on these cars...Jim '85TE
Thanks guys. I added a syringe full of oil into each cylinder bore and re-measured the compression. I got a figure of about 135 psi. I do not consider this to be a very significant rise (WHAT DO YOU THINK?), therefore I think I can rule out rings / bore wear. The figures I have been getting have been done both with the throttle fully open and closed. Strangely enough the figures do not change. I looked at the filter and it has only just been replaced and is fine. Also the inlet to the turbo is not blocked. The performance is very good and the idle is only very slightly erratic. Still not checked valve timing, but may also look at valve clearances. If there is insufficient clearance (despite reset by dealer) then the valves will open for longer and compression may suffer? I managed to get the car to boost lower by lengthening the w/gate actuator rod, but then the turbo wouldn' t boost until about 3,500 rpm around town. On the motorway, under load, the boost comes earlier. I have subsequently reset the rod to it' s original position. There is a slight amount of pre-load on the spring at the point the rod slides onto the wastegate lever. Is this correcy?
Does your car idle OK?
My SE when comp tested had 120 too exact on all four cylinders and it has full LSH I checked the valve timming and it was spot on having just had the head gasket replaced its performance is excellent but its idling was rough until I fitted a new IAC valve as this controls air by-pass in your inlet manifold this may affect the comp and vac readings.
Good luck
Mike(UK)
My SE when comp tested had 120 too exact on all four cylinders and it has full LSH I checked the valve timming and it was spot on having just had the head gasket replaced its performance is excellent but its idling was rough until I fitted a new IAC valve as this controls air by-pass in your inlet manifold this may affect the comp and vac readings.
Good luck
Mike(UK)
danny tattersall said: Thanks guys. I added a syringe full of oil into each cylinder bore and re-measured the compression. I got a figure of about 135 psi. I do not consider this to be a very significant rise (WHAT DO YOU THINK?), therefore I think I can rule out rings / bore wear. The figures I have been getting have been done both with the throttle fully open and closed. Strangely enough the figures do not change. I looked at the filter and it has only just been replaced and is fine. Also the inlet to the turbo is not blocked. The performance is very good and the idle is only very slightly erratic. Still not checked valve timing, but may also look at valve clearances. If there is insufficient clearance (despite reset by dealer) then the valves will open for longer and compression may suffer? I managed to get the car to boost lower by lengthening the w/gate actuator rod, but then the turbo wouldn' t boost until about 3,500 rpm around town. On the motorway, under load, the boost comes earlier. I have subsequently reset the rod to it' s original position. There is a slight amount of pre-load on the spring at the point the rod slides onto the wastegate lever. Is this correcy?
Danny,
Valve clearance is of course critical to proper engine operation. The the valve clearnce spec on Esprit engines is 0.005"-0.007" for intake valves and 0.010"-0.012" for exhaust valves. It's important to set these to the 'outside' values (0.007" & 0.012") This is because this gap closes with time as the valves are continually pounded deeper into the valve seats. Setting to these values increases the time allowed between resetting the clearances. Happy Motoring Jim '85TE
If it was a matter of valve clearances surely the would be different readings on each cylinder as it is very unlikely they would all be out by the same amount.
Also in my cars case the head had just been set up by a specialist with new valve guides etc due to replacing the head gasket.
I was also informed that after having the head done the clearances should be checked at 1000 miles The four pot Lotus engines are notorious for loosing there clearances after a rebuild or from new as the valves settle in their seats
Regards Mike
Also in my cars case the head had just been set up by a specialist with new valve guides etc due to replacing the head gasket.
I was also informed that after having the head done the clearances should be checked at 1000 miles The four pot Lotus engines are notorious for loosing there clearances after a rebuild or from new as the valves settle in their seats
Regards Mike
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