M20b25 Cam question

[CrJdMc]

So I know the basics to replacing the cam in my 87 325is, I have an ie cam to put in. I know I have to loosen the tensioner to get the timing belt off, and then take the valve cover off, what else is there to do? I was told I need to move the rockers to the side, does anyone have any rather descriptive steps to move the rockers over and anything else I need to do? Please and thank you.

[SkiFree]

With all due respect, I'd highly HIGHLY suggest buying a Bentley or Haynes (or downloading the .PDF files found on R3v) repair manual. They'll go over cam replacement with step by step instructions.


Couple further notes
Be sure to check the condition of your rockers and rocker shafts. Nothing will eat a new cam like out-of-spec rocker pads. Be sure to use an oil with the proper amount of ZDDP, and do a basic break in procedure to bed the new cam and (inspected) rockers.

[CrJdMc]

May I ask what the basic break in procedure is?

[nando]

you're going to have a really rough time replacing the cam with the head on the car.

also, a bone stock, high miles engine with old rockers, old valve springs and worn out valves with a new performance cam is a recipe for disaster.

[CrJdMc]

Oh really? Would you all suggest building a head to put on all at once?

[SkiFree]

Oh really? Would you all suggest building a head to put on all at once?

That would be the ideal way to do it. Or at a minimum have a machine shop check the springs/rockers/flatness/valveguides.

In regards to cam/rocker break in, this is an exert from a nearly finished engine break in article, once finished it will be in the Ireland Engineering tech section.

"The first time the engine is started, it should be run at a static 2000-2500RPM for 12-15 minutes, for initial bedding of the cam and rocker wear surfaces. During this first run, it's a good idea to place a floor fan in front of the car to keep air moving through the radiator. "

[jlevie]

"The first time the engine is started, it should be run at a static 2000-2500RPM for 12-15 minutes, for initial bedding of the cam and rocker wear surfaces. During this first run, it's a good idea to place a floor fan in front of the car to keep air moving through the radiator. "

An acquaintance that worked professionally as a NASCAR engine builder recommended 30 minutes at 2500rpm after the engine had stabilized at normal operating temperature. If the cooling system of an M20 engine is operating properly, there'll be no need for a cooling fan. He also recommended engine oil as an assembly lube.

Before I start the engine I use a 3/8" corded drill to spin the oil pump shaft to push oil to all bearings. During the break in I have the car up on jack stands to make it easy to check for leaks. And I always have a temporary oil pressure gauge connected so I can monitor oil pressure and use an IR thermometer to monitor head temperature during the break in.

These engines want an oil with a high ZDDP content and there is no advantage to synthetic over conventional oil because you can't take advantage of synthetic's longer life (the oil & filter need to be changed no less often than the factory schedule). I use Brad Penn 20w50 and do the first oil filter change 500mi after breaking in the engine. Valvoline VR1 is a more readily available oil that is almost as good.

[SkiFree]

An acquaintance that worked professionally as a NASCAR engine builder recommended 30 minutes at 2500rpm after the engine had stabilized at normal operating temperature. If the cooling system of an M20 engine is operating properly, there'll be no need for a cooling fan. He also recommended engine oil as an assembly lube.

Good to have your input Jim, think 30min might be a little overkill in this case, however I'm sure it wouldn't hurt (I think we could split hairs for a while though if we wanted). The cooling fan was just in case the cooling system was not operating properly and was not actively being monitored (call it a safety precaution against stupidity).

As for everything else I agree completely. It could be added, do a valve adjustment after the first heat cycle.

[jlevie]

Good to have your input Jim, think 30min might be a little overkill in this case, however I'm sure it wouldn't hurt (I think we could split hairs for a while though if we wanted). The cooling fan was just in case the cooling system was not operating properly and was not actively being monitored (call it a safety precaution against stupidity).

A pretty powerful cooling fan certainly won't hurt, but monitoring engine temperature with an independent instrument that can be verified for accuracy is more important. The gauge could be lying, there could be an air bubble at the sensor, etc.

In this case (just head work) 30minutes is excessive. I was really my directing my comment to you nascent document

As for everything else I agree completely. It could be added, do a valve adjustment after the first heat cycle.

Good point, I do a valve adjust at the 500mi oil change.

[CrJdMc]

Thanks alot guys. I guess it'll be a while until I have the new head on, oh well better safe than sorry