M20 intermediate shaft failure

[Knoopa]

I have built a stroker engine but after putting it in the car and just driving a few kilometers it started to develop a loud knocking sound. After tearing the engine apart again I saw that the intermediate shaft got shaved by the clip that’s retaining it which has caused massive play on the intermediate shaft and the metal shavings caused the rod bearings of cilinder 1 to be spun.

So obviously I need a new intermediate shaft, a new rod and some bearings. However I have no idea why this happened and don’t want to spent a lot of money just for the same thing to happen again. Couldn't find something similar on Google either. One thing I have noticed is that the shaft can be easily inserted and removed into the block without force. However I have a b20 block here where I tried to put the shaft and it requires a bit of force which led me to believe that the bearings have too much clearance.

Could too much bearing clearance have caused this? And if so how can these bearings be replaced because as I understand those are pressed in with a specialised tool by BMW.

Did anyone here ever had similar issues or know what could have caused this. I’m really clueless, everything is basically new and measured to spec.

[zaq123]

Is that original intermediate shaft to the block? That retainer grove looks way too wide. It should be not much wider than the retainer itself? Or the shaft journal really got chewed up that bad? Was block hot tanked as a part of your build? Was shaft bearing replaced as a part of the build? There should be 0.001-.00015" clearance so I would not call it as a tight fit but should be wobbling in there. It should feel similar fto how the camshaft is in the head which has slightly larger clearance which I believe is about 0.0015" to 0.002"

[Knoopa]

Is that original intermediate shaft to the block? That retainer grove looks way too wide. It should be not much wider than the retainer itself? Or the shaft journal really got chewed up that bad? Was block hot tanked as a part of your build? Was shaft bearing replaced as a part of the build? There should be 0.001-.00015" clearance so I would not call it as a tight fit but should be wobbling in there. It should feel similar fto how the camshaft is in the head which has slightly larger clearance which I believe is about 0.0015" to 0.002"

Yes the retainer groove was chewed up, it wasn’t like that when I built the engine. The block got cleaned by the machine shop so I assume they hot tanked it. It does fit pretty tight but I can slide it in and out by hand easily, when putting it in the b20 block where it originally came from I need to apply some force to push it in.

However the main question is if too much bearing clearance would cause this. It seems like something pushed the shaft towards the retainer which led to it chewing itself but it’s hard to imagine that a little bit too much bearing clearance would cause that. But as that retainer is the only thing holding it in place I can’t really think of anything else that could have caused this.

[digger]

I’m really clueless, everything is basically new and measured to spec.

the intermediate (IM) shaft itself was new, or if not was it original to the block?
the IM bearings were new/replaced? what do they look like now?
the thrust plate was new or used?
how was the meshing of the gears when assembling the engine?
were the needle bearings replaced?

it looks like lack of lubrication or of overload binding cause high thrust

[Knoopa]

the intermediate (IM) shaft itself was new, or if not was it original to the block?
the IM bearings were new/replaced? what do they look like now?
the thrust plate was new or used?
how was the meshing of the gears when assembling the engine?
were the needle bearings replaced?

it looks like lack of lubrication or of overload binding cause high thrust

The shaft itself was taken from my B20 block, so it was not new but was still in very good shape. The bearings were not replaced but seemed in good condition as well, from what I've read those can't be replaced easily. Right now they are pretty scored up which is to be expected as the metal shavings of the shaft also messed up the rod bearings. The meshing of the gears was and is still good, the gear inside the block was replaced with a new one.

What's weird is that I can't find any reports of similar issues, only of lower oil pressure when the bearings had too much clearance. As long as I don't know what caused it I can't put the engine back together as there will be a chance it will just happen again even after replacing the shaft and bearings.

[zaq123]

you can't use intimidate shaft from another engine or a new shaft unless you put new bearings and cut them to match that shaft. Every m20 has that bearing pressed in and then cut to match the intermediate shaft for that motor only. Why I asked if the shaft is original to the block...that particular block, how it came from the factory.

There are a couple of things you can never use from another block on M20 without doing further modifications: a) crankshaft main bearing caps, B) intermediate shaft.

[Knoopa]

you can't use intimidate shaft from another engine or a new shaft unless you put new bearings and cut them to match that shaft. Every m20 has that bearing pressed in and then cut to match the intermediate shaft for that motor only. Why I asked if the shaft is original to the block...that particular block, how it came from the factory.

There are a couple of things you can never use from another block on M20 without doing further modifications: a) crankshaft main bearing caps, B) intermediate shaft.

Yeah I just got a bare block so it didn't come with a shaft unfortunately. As both the shaft and bearings are ruined they will both need to be replaced anyway so that would solve that. However it seems like chewing away metal like this would require quite some force pushing back on the shaft. I have seen reports of low oil pressure with too much bearing tolerance but nothing like this, do you think this could have caused the shaft to be chewed up like that?

[zaq123]

Think of this scenario: clearance is too large which makes the shaft to sit cocked in there, against the retainer edge like against freaking lathe blade. All that tension from the timing belt is trying to pull that cocked shaft out. Clearance is so large that there is not enough pressure to built any sort of oil layer between the shaft and bearing to counter the belt tension. Cocked shaft, no pressure, lots of tension from the timing belt...

Just my version of what happened.

Don't forget to measure clearance on both bearings when pressed into the block. Why those bearing and/or shaft need to be cut and measured only after pressed into the block.

[Knoopa]

Think of this scenario: clearance is too large which makes the shaft to sit cocked in there, against the retainer edge like against freaking lathe blade. All that tension from the timing belt is trying to pull that cocked shaft out. Clearance is so large that there is not enough pressure to built any sort of oil layer between the shaft and bearing to counter the belt tension. Cocked shaft, no pressure, lots of tension from the timing belt...

Just my version of what happened.

Don't forget to measure clearance on both bearings when pressed into the block. Why those bearing and/or shaft need to be cut and measured only after pressed into the block.

That does make sense, I have an oil pressure sensor in a sandwich plate between the block and filter and oil pressure was good there but it might have been different between the shaft and bearings of course. I don't have the equipment to press those bearings in the block so I would have to trust the machine shop to do that correctly. It would be better to find someone with experience on these engines instead of a generic machine shop I guess.

[zaq123]

That does make sense, I have an oil pressure sensor in a sandwich plate between the block and filter and oil pressure was good there but it might have been different between the shaft and bearings of course. I don't have the equipment to press those bearings in the block so I would have to trust the machine shop to do that correctly. It would be better to find someone with experience on these engines instead of a generic machine shop I guess.

yes, your sensor is located to read pre filter pressure right after the oil pump. Digger can tell you more but if remember correctly, intermediate shaft oiling holes are at the end of the oil gallery run for that direction and after that oil is just being squeezed to lube shaft gears (back bearing) and shaft retainer (front bearing). Obviously pressure loss there will still affect reading in the whole system but a total loss of pressure at the shaft won't show you no pressure sensor at the pre-filter location.

I wouldn't go looking much into why and how ... because with 99.9% certainty you can be sure that that foreign shaft and your block shaft bearings weren't meant to be as installed. If you are super curious, measure the clearance (OD diameter of shaft journals vs ID of the bearing ) if you got all right tools and report back.. You need tools with 0.01mm resolution accuracy as I've mentioned the clearance there 0.001-.0015" (0.025-0.038 mm). Most sliding calibers are like 0.03mm resolution but if your clearance is extremely out of spec, that would show it too to satisfy your curiousity

[Knoopa]

I wouldn't go looking much into why and how ... because with 99.9% certainty you can be sure that that foreign shaft and your block shaft bearings weren't meant to be as installed. If you are super curious, measure the clearance (OD diameter of shaft journals vs ID of the bearing ) if you got all right tools and report back.. You need tools with 0.01mm resolution accuracy as I've mentioned the clearance there 0.001-.0015" (0.025-0.038 mm). Most sliding calibers are like 0.03mm resolution but if your clearance is extremely out of spec, that would show it too to satisfy your curiousity

The main reason I wanted to know how it happened is to make sure it doesn’t happen again. Because of this I need to replace at least one rod, all rod bearings and probably the main bearings as well. As those parts were all new that is a lot of money down the drain so obviously I don’t want to put everything back together just to be in the same situation.

It does make sense though that the issue was caused by the shaft block mismatch so hopefully replacing both the shaft and the bearings will fix it. I don’t think measuring things makes sense at this point as the clearance is already affected by the metal shavings in the oil.

[82eye]

if they hot tanked it they destroyed the babbitt bearing for the intermediate shaft. you can't hot tank it with the bearing in.

edit: the issue won't be a mismatch. all im shafts are the same spec.

the only time anything changes is when you remove the bearing itself. the specs and shafts are not individual to the engine at all. if you remove and hone the area for the bearing, then you have to check the bearing spec for the right one. they are all identical from factory otherwise.

[digger]

There is evidence of the front bearing flaking away and rear bearing edge loading so perhaps it was the rotation cuased by failure / damaged bearing from hot tanking or fatigue causing thrust issues.

Was the thrust plate new? Note that the shaft is only case hardened cast iron so once it wears a bit it will accelerate wear rapidly and it is hard to examine the surface of the thrust groove.

Fortunately most parts are still available new AFAIK so any potential cause can be fully addressed.

As an alternative to the factory bearings John (forced firebird here) sells these which are a little more straight forward to install has boring and honing bronze is a more correct process than honing the uber soft factory ones. I have a set which I will probably use on my next engine but haven’t used a set yet.

https://www.ebay.com.au/itm/235343763965?

[zaq123]

if they hot tanked it they destroyed the babbitt bearing for the intermediate shaft. you can't hot tank it with the bearing in.

edit: the issue won't be a mismatch. all im shafts are the same spec.

the only time anything changes is when you remove the bearing itself. the specs and shafts are not individual to the engine at all. if you remove and hone the area for the bearing, then you have to check the bearing spec for the right one. they are all identical from factory otherwise.

A lot of agitating hot tanks are only run at 160-180F. So tanking obviously may or may not destroyed the bearing if the block was indeed hot tanked. If it was lye activated hot tank, it will destroy that bearing regardless of the temp but a shop will not put any blocks with babbit into the hot tank and ask for babbitt removal because their lye will be no good in the tank after this. So all this needs more info from the shop.

lHowever how certain are you that all shafts, especially used ones are the same? Everything needs to be measured in my opinion.

[82eye]

A lot of agitating hot tanks are only run at 160-180F. So tanking obviously may or may not destroyed the bearing if the block was indeed hot tanked. If it was lye activated hot tank, it will destroy that bearing regardless of the temp but a shop will not put any blocks with babbit into the hot tank and ask for babbitt removal because their lye will be no good in the tank after this. So all this needs more info from the shop.

i've seen them ruined by a hot tank here. i've also advised shops on them who have told me they have no idea about them. many shops here don't know how the m20 intermediate shaft is installed.

lHowever how certain are you that all shafts, especially used ones are the same? Everything needs to be measured in my opinion.

replaced a couple. bmw did not have a technician that sat honing each engine individually. new shafts are still available, and we've put at least one new shaft in before on a new bearing with no issue, and have installed a used shaft from a different engine with a new bearing over the same hot tank problem on another engine.

you are absolutely correct in the best practice always being keeping the original shaft with the original engine if possible. we've just never found it to be a problem.