Leak Test Results

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pos

pos

Well-Known Member
Posts
3,685
Location
West Yorkshire
Hello,

I carried out a leak test on my 200tdi on Saturday and I would like your opinions on the results please. I carried out four tests per cylinder and then took the average in each case. The piston was positioned at TDC on the relevant cylinder at the time of the test. In some cases, the pressure from the air line would force the piston down and turn the engine over very slightly until it was stopped when the pressure could not overcome the resistance from the gearbox. All tests were taken with the gearbox in second gear.

Cylinder 1: 92%
Cylinder 2: 92%
Cylinder 3: 92%
Cylinder 4: 94%

I would have said that these are relatively good results but I would like a second opinion. I find it interesting that cylinder no.4 is slightly more efficient given that I know the tappets are set with a very slightly larger clearance than the remaining three cylinders. I had the rocker shaft off last week, so I obviously need to re-reset the clearances on this cylinder (I did set them all at the time). BUT... would this suggest that it is possible my cam timing is out one to two teeth and at least one of the valves of cylinders 1,2,3 are slightly open when the piston is at TDC?

Thanks,
-Tom
 
you should have both valves closed or on the rock on opposing cylinder 1 and 4 3 and 2 at tdc ,both closed for combustion ,both open for end of exhaust begining of induction
 
jamesmartin said:
you should have both valves closed or on the rock on opposing cylinder 1 and 4 3 and 2 at tdc ,both closed for combustion ,both open for end of exhaust begining of induction
Click to expand...

You've confused me a little there, could you explain it a little differently? What do you think of the readings I got? Do they seem good or poor?

Thanks,
-Tom
 
remove the rocker shaft so all the valves are clossed then place the piston at bottom dead center and do the same test ..... just to be shure nothing is bent or worn then do it with the rocker shaft back in place and the "tappets" correctly adjusted and rocking on there fire stroke ie both valves fully closed and piston near or at tdc ...can i ask what fault your looking for ? ....if the cam timeing is out wouldnt it be just as easy to check / adjust that ? ....
 
jamesmartin said:
at tdc one piston will have 2 open valves other 2 shut ,test would suggest good cylinders valves etc
Click to expand...

I thought that if piston no.1 was at TDC, both valves on that cylinder would be tight shut as the compression stroke ends and the power stroke begins? As piston no.1 reaches TDC, the valves on cylinder no. 2 would be rocking between the exhaust valve closing and the inlet valve opening would they not? :confused:
 
bennybenny said:
remove the rocker shaft so all the valves are clossed then place the piston at bottom dead center and do the same test ..... just to be shure nothing is bent or worn then do it with the rocker shaft back in place and the "tappets" correctly adjusted and rocking on there fire stroke ie both valves fully closed and piston near or at tdc ...can i ask what fault your looking for ? ....if the cam timeing is out wouldnt it be just as easy to check / adjust that ? ....
Click to expand...

Thanks for your reply. What would be the benefit of a leak test with the piston at bottom dead centre? Would it be solely to take a "snapshot" of the entire volume of the bore as so to speak rather than just the top end where the combustion takes place? My engine is suffering from white / blue smoke and a horrible misfire from a cold start and an irratic, hunting idle once warm. I have gone through everything you can imagine. Air in fuel, injectors, injection pump, lift pump, filters, hoses etc. I am suspecting that i have either a burnt valve / bad valve seat or a worn keyway on either the cam or crank.
 
tdc on 1 is tdc on 4 at same time one cylinder will be both valves shut about to start combustion stroke ,other both valves open ,exhaust shutting inlet opening about to start induction the same with 2 and 3 ,
 
pos said:
Thanks for your reply. What would be the benefit of a leak test with the piston at bottom dead centre? Would it be solely to take a "snapshot" of the entire volume of the bore as so to speak rather than just the top end where the combustion takes place? My engine is suffering from white / blue smoke and a horrible misfire from a cold start and an irratic, hunting idle once warm. I have gone through everything you can imagine. Air in fuel, injectors, injection pump, lift pump, filters, hoses etc. I am suspecting that i have either a burnt valve / bad valve seat or a worn keyway on either the cam or crank.
Click to expand...

reason to check when at the bottom is you are then also checking the boar for damage scratches and so on, the piston when the engine is running use's all of its stroke so any fault in any area of the system can affect things .....all the time you have spent doing this test wouldnt it have been a idea to rip the head off and actually take a peek inside lol ..?
 
jamesmartin said:
tdc on 1 is tdc on 4 at same time one cylinder will be both valves shut about to start combustion stroke ,other both valves open ,exhaust shutting inlet opening about to start induction the same with 2 and 3 ,
Click to expand...

Oh I see what you mean now, I just couldn't get my head around it at first! :D So what next with regards to my problem then!? I think I need to take a second look at my timing, radiator / intercooler out so I can look straight on at the engine. I will also remove the cam + crank pulleys and check that the keyways are not worn and that the key's are tight / in place.

Other than that, well I don't have a clue.

-Tom
 
pos said:
Oh I see what you mean now, I just couldn't get my head around it at first! :D So what next with regards to my problem then!? I think I need to take a second look at my timing, radiator / intercooler out so I can look straight on at the engine. I will also remove the cam + crank pulleys and check that the keyways are not worn and that the key's are tight / in place.

Other than that, well I don't have a clue.

-Tom
Click to expand...

fire would fix it lol ...... you fitted a cambelt recently ?
 
both valves would have been shut unless badly set tappets ,as engine if run would have been very noticeably bad, but i allways remove rad so i can get battery gun in and is better to look straight on for cam ,if mark cant be exact aim for slightly advanced(mark on pulley top side of case mark rather than bottom)
 
jamesmartin said:
both valves would have been shut unless badly set tappets ,as engine if run would have been very noticeably bad, but i allways remove rad so i can get battery gun in and is better to look straight on for cam ,if mark cant be exact aim for slightly advanced(mark on pulley top side of case mark rather than bottom)
Click to expand...

I am going to set them all again tomorrow night ready for my trip darn sarth over the weekend. A quick question. I have never ever replaced the idler / tensioner pulleys in the timing case. Is it possible that one might have ceased / worn to the extent that it will effect the tension / rotation of the belt?

-Tom
 
possible but youd soon find out as belt smoked and rods bent ,i just stripped a smokey engine ran well ,most push rods a little bent,but yours is intermittent ?
 
jamesmartin said:
possible but youd soon find out as belt smoked and rods bent ,i just stripped a smokey engine ran well ,most push rods a little bent,but yours is intermittent ?
Click to expand...

I did have a bent pushrod. I know all eight were straight a year ago when I did the head gasket but when I checked the pushrods in the summer when the problem began to really annoy me I found one bent pushrod. I swapped it, and when I checked them all again the other week, they are all still straight. So, something bent it between me doing the head and me checking earlier this year. It is an intermittent problem yes. Sometimes it will idle beautifully, sometimes it will hunt very strongly (seemingly on just one cylinder), so much so that my 90 rocks side to side with it. Sometimes it will just be a very quick misfire. It ALWAYS produces Blue / white smoke from a cold start if I deck the pedal but it also gives the usual puff of blacksnake from a cold startup too. If I rev and maintain a high idle when warm, it produces a bit of blue smoke from the exhaust which instantly blackens if I blip the throttle.

-Tom
 
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