Hi
Just rebuilt an M20 engine and converted into a M20B29 stroker using the M52B28 crank with Mahle motorsport pistons, forged internals, new flowed and ported old stock 885 head with all modifications you can think of and so on.
This week we started it up for the first time on Motul 10W40 mineral break in oil (car has not driven yet) but we immediately saw a lack of oil pressure. Cold we have 72psi at 2000 RPM. Warm on 2000 RPM we have 26psi, 3000 RPM 35psi, which is not enough.
- Crankshaft bearings (ACL) tolerance 0,0027inch. Due to the application chosen for this but still within BMW specs.
- Conrad bearings (BMW) tolerance 0,0015inch, which is well within specs.
- Intermediate shaft bearings were also replaced as these where shot. Placed new ones with tolerance 0,0017inch or 0,045mm. My mechanic rebuilt engines for a living (S50, S54, M30), however never replaced intermediate shaft bearings on an M20 so this is the only thing we didn't ourselves.
- oil pump is new.
We already replaced the pressure relief valve by a new one, replaced the new oil pump by a spare one, checked the two pumps internally but everything is ok. Headwise everything is also ok, however we still have this lack of oil pressure. We tested also with different oil pressure meters, which all show the same result.
As for our understanding we don't think that some oil wholes should be plugged in this stroker setup. I also don't think that this is a problem from using break in oil, as viscosity is 10w40.
The only thing we can think of is the only thing we didn't do ourselves: the intermediate shaft bearings. The person who did this used honing stones, however I must admit it was fairly rough done, as you can see in the pictures. I still remember that I felt the contours with my fingernail.
Could this result in the problem we have?
I have a spare of new bearings, so we are thinking of placing them ourselves this time. I already sent a pm to #ForcedFirebird so I hope he reads it as he manufactured some tools to do the job. I know he uses 0,001inch (0,026mm) tolerance so this is different from the 0,0017inch we applied. What do the racers here to increase oil pressure?
Anyone else who's thinking at other causes or already had this problem with the shaft bearings?
Thanks for you help.
Gregory
Just rebuilt an M20 engine and converted into a M20B29 stroker using the M52B28 crank with Mahle motorsport pistons, forged internals, new flowed and ported old stock 885 head with all modifications you can think of and so on.
This week we started it up for the first time on Motul 10W40 mineral break in oil (car has not driven yet) but we immediately saw a lack of oil pressure. Cold we have 72psi at 2000 RPM. Warm on 2000 RPM we have 26psi, 3000 RPM 35psi, which is not enough.
- Crankshaft bearings (ACL) tolerance 0,0027inch. Due to the application chosen for this but still within BMW specs.
- Conrad bearings (BMW) tolerance 0,0015inch, which is well within specs.
- Intermediate shaft bearings were also replaced as these where shot. Placed new ones with tolerance 0,0017inch or 0,045mm. My mechanic rebuilt engines for a living (S50, S54, M30), however never replaced intermediate shaft bearings on an M20 so this is the only thing we didn't ourselves.
- oil pump is new.
We already replaced the pressure relief valve by a new one, replaced the new oil pump by a spare one, checked the two pumps internally but everything is ok. Headwise everything is also ok, however we still have this lack of oil pressure. We tested also with different oil pressure meters, which all show the same result.
As for our understanding we don't think that some oil wholes should be plugged in this stroker setup. I also don't think that this is a problem from using break in oil, as viscosity is 10w40.
The only thing we can think of is the only thing we didn't do ourselves: the intermediate shaft bearings. The person who did this used honing stones, however I must admit it was fairly rough done, as you can see in the pictures. I still remember that I felt the contours with my fingernail.
Could this result in the problem we have?
I have a spare of new bearings, so we are thinking of placing them ourselves this time. I already sent a pm to #ForcedFirebird so I hope he reads it as he manufactured some tools to do the job. I know he uses 0,001inch (0,026mm) tolerance so this is different from the 0,0017inch we applied. What do the racers here to increase oil pressure?
Anyone else who's thinking at other causes or already had this problem with the shaft bearings?
Thanks for you help.
Gregory
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