I dont have any experience with these engines, but it looks like the M73 has a higher compression ratio than the M70, 10.0 vs 8.8. If the combustion chambers aren't radically different between the two heads where you can maintain the higher compression ratio using the M70 heads on the M73 block then I would definitely run the M70 heads with the Shrick cams. I wonder what the piston tops look like in each engine? Did they change the piston design to up the compression ratio or did they reduce the combustion chamber dimensions?
Maybe there is some improvement to gain with porting, polishing, and a valve job.
Last edited by JDP530; 12-30-2017 at 02:22 PM.
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
Trying to perform a leak down test with donor engine. Is it even worth it on the stand though? I obviously can’t get it up to operating temperate and besides that it’s freezing here. While I have a heater in the garage, it’s still cold.
Also, any suggestions on the best way to find TDC per cylinder. It’s not as easy as the 6s because of the angle of the spark plug hole to the piston top. so the screwdriver trick doesn’t seem to be very accurate.
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'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
A bent piece of wire in the spark plug hole should get you close, and if the valve covers are off, you will see when both valves are closed. The leak down test will be consistent since all the cylinders are cold. A compression test is quicker and a reasonable way to compare the cylinders condition.
Last edited by 72tpik5; 01-01-2018 at 04:01 PM.
Desecrator of all things Sacred
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
Last edited by 72tpik5; 01-02-2018 at 12:12 AM.
Desecrator of all things Sacred
are you aware that the M73 bell housing bolt pattern is different to the M70 and thus will not bolt directly to the M70 gearbox/auto
I believe it has the same bolt pattern as the M50/2/4 range of motors so a E46 or E36 s6s420g will fit or perhaps a GS6-53DZ from a Euro 330 or 325
I am 95% certain of this fact and i would like confirmation of this before i get too involved in the project i have in mind
which is i have an 850csi with a seized motor in the meantime i intend on inserting a M73 with a manual trans which to all intensive purposes will look,go and preform nearly as well as the original csi with a small side benefit of the s6s420 having the better gear change than the csi 6 speed and without the worry of the csi box self destructing
brian
Those Schrick cams will most likely not fit. To my knowledge Schrick only produces cams for M70 engines (and heads).
- - - Updated - - -
definitely NOT TRUE. The 4HP24 and / or 6-speed getrag fit to the M73 block without any problem. I've done it several times.
The large oil pan has a slightly different bolt pattern on the M73, but not the bell housing. Maybe you are mixing up something here.
Yes it did seem a little strange but a friend who works at a bmw wreaker/repair shop tried to fit a 5hp30 from a m60 to an e38 750 e38 750il ams couldn't he said it was the 6cyl bolt pattern which would be awesome if it were true mainly because of the multitude of gearbox options that it would create but logically why would bmw do that
I suppose I will find out for sure when I get the cheap 750il I bought delivered
M60 is different from M70 / M73. Not only in terms of cylinders. 😁
TDC is not super critical, I just stick a long plastic stick down cyl and observe valves to ensure on compression cycle. If you are off TDC the air pressure will rotate the engine. Expect to have to rock the crank a little for best results.
Starter motor is the way to turn motor for a compression test.
Yes sir. Totally clear on that. I’m still trying to decide whether to go straight swap with M73 heads or the Wokke special M73 bottom end and M70 heads with the Schrick cams. Pros and cons both ways, so trying to make the best long term decision as this is a keeper car for me.
If I can get into the same performance ballpark with the straight M73 swap, then leaning towards that. Just trying to understand how to get the tune on the M70 electronics for the M73 bits.
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'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
Awesome. Well. Took your advice last night and started tearing in. Long story short, engine hoist I bought was missing critical parts... super frustrating. So don’t have it on the stand yet. Started tearing into top end.
Most of the calves were pretty clean, but some carbon build up on a few. Recommendations for cleaning up with heads still on?
I need to take better pics of the cams as this angle is bad. But heads look pretty clean. Cams look good. No visible scoring or unusual wear. The oil spray bar on these heads is certainly way better than the M70!
Did some additional research on the exhaust down pipes for the M73. It does NOT look as though the later E31 M73 downpipes will match up to the ‘91 stock exhaust. So, will still need to address that piece.
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Last edited by adwebinc; 01-02-2018 at 04:14 PM.
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
'07 e65|N62 - Alpina B7 - Black Sapphire|Black|Loaded|GONE
'02 e46|M54 - Orient Blue|Beige|'Vert|GONE
'00 e39|M52 - Anthrazit Metallic|Grey|GONE
'01 e38|M73 - Anthrazit Metallic|Schwarz|Shadow-Line|GONE
'91 e31|M70 - Schwarz|Schwarz|M70|FOR SALE
'13 328i Auto - Black Sapphire|Coral Red|Sport Line|GONE
'05 545i SMG - Jet Black|Black|Bamboo Anthracite|GONE
'07 335i Auto - Montego Blue|Grey|GONE
'05 545i SMG - (Euro Delivery 7/22/05)|Black Sapphire|Auburn|GONE
'97 528i Auto - GONE
I don't know about where you are (I'm in San Diego) but I was able to buy CRC gasket remover (red can) at my local O'Reilly's for ~$6.50/can. Only a few stores had it in stock but all can get it in a few days. This is much cheaper than buying online (no shipping).
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