Bent Con rod- how to tell?

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DaveyGTi

DaveyGTi

Well-Known Member
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239
Location
Hastings
OK, see my previous thread about flushing the diesel pump for the full story.
I've now got my engine running again having cleaned out more or less everything and replaced the lift pump and I'm now more or less ready to go apart from fitting a new air filter and changing the oil but before I do that and dump in £40 of fresh oil I want to tell if any of the con rods are bent, is there a quick and easy way to do that? Engine seems to run OK, was just fractionally less willing to start than before, could that just be it getting rid of a bit of crap? I also noticed when pulling the dipstick out the oil was a little cloudy- not white/foamy/milky as if the head gasket had gone, just slightly opaque- again could that just be ingress of crap easily sorted with a flush and fresh oil?
 
Compression test .
If they are all similar (approx 400 psi) you won't have a bent rod. If you have low reading(s) then, if it's not a valve or other issue, the head will have to come off as James says.
 
Yup compressions test. It wont rule out a bent rod but if there is a drop on one cylinder then it's fairly certain one is bent. If theres no pressure at all on one then you've a holed or cracked piston instead.
 
Pull the glow plugs or injectors and try turning the engine over by hand, if it feels really stiff then there is a chance that a rod is bent (don't forget the valve springs. FIP will also add a bit of resistance. Best way is head off and check the piston crown heights above the deck, all should be similar, if not there is your bent one.
 
Can you not pull the injectors insert a rod then turn the engine & mark the height on the rod
if one is bent you should have some sort of resistance.
 
DaveyGTi said:
OK, see my previous thread about flushing the diesel pump for the full story.
I've now got my engine running again having cleaned out more or less everything and replaced the lift pump and I'm now more or less ready to go apart from fitting a new air filter and changing the oil but before I do that and dump in £40 of fresh oil I want to tell if any of the con rods are bent, is there a quick and easy way to do that? Engine seems to run OK, was just fractionally less willing to start than before, could that just be it getting rid of a bit of crap? I also noticed when pulling the dipstick out the oil was a little cloudy- not white/foamy/milky as if the head gasket had gone, just slightly opaque- again could that just be ingress of crap easily sorted with a flush and fresh oil?
Click to expand...
If it looks like this.
images
or like this
Bent_connecting_rod_1.JPG
 
Low compression on one cylinder doesn't necessarily mean a bent rod. In fact that would be my last consideration. Do as kevstar says and insert a measuring rod down the injector holes. If your still not sure the head will need to come off. I can't be arsed looking up your old posts and my memory is only good for a few nano seconds so why do you think you have a bent rod.

Col
 
kevstar said:
Can you not pull the injectors insert a rod then turn the engine & mark the height on the rod
if one is bent you should have some sort of resistance.
Click to expand...

You can but there are a few things to consider - you cannot control easily where the end of the rod lands on the piston. Hopefully it lands in the swirl pot in the same place.... and there is no carbon gunk on the crown..

Also the glow plugs are on different locations relative to the block, so the rod length is going to be different. I suspect that you will find you get two figures for an OK engine, 1 and 3 similar 2 and 4 similar. It will show up a grossly bent rod however I would have thought.
 
In this picture posted on your other post the badly bent conrod was from number three cylinder the other was from number four cylinder.
As the firing order is 1342 I could not see how four could have got bent at the same time as three so maybe had been running bent for awhile.Three can be seen in 2nd pic as below two's level the conrod was actually jammed against the cylinder lower skirt and had took a piece of the skirt off.

IMG_1479.JPG IMG_1409(1).JPG DSCF3441.JPG
 
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