Finding top dead center on the head of a 1986 bmw 325

[nnastye30]

looking for help for finding top dead center on the head of a 1986 bmw 325. **The head is off of the car** I took the head to a machine shop to be resurfaced and i got the head back not in top dead center anymore so i am lost as how to figure out where TDC is

I understand i can put the pulley back on and align the arrow to see where it is, but how could i be sure it is at the right alignment? How can i be sure its not at TDC of the compression stroke and not the power stroke?

I have looked through forums and also purchased a BMW service manual and haven't been able to find anything about this

Is it possible that all i need to do is align the arrow to the marking? That wouldnt make much sense, because when setting it at TDC with the head in the car you need both the camshaft pulley and the harmonic balancer to align, not just the camshaft pulley. meaning just because the camshaft pulley arrow is pointing aligned doesnt mean its aligned.

Really dont want to bend any valves, thanks for the help in advance

[msservices]

If the head is off the car, TDC should be with no. 1 piston at the top of its stroke. Whether that will become top of the compression stroke or top of the exhaust stroke is determined by the head/valve train when it gets installed. That’s the main reasoning they put, and you line up the marks on the cam and the crank upon installation. If you did not have the cam mark to reference, then your question would be legitimate and require looking into the cam/rocker positions for cylinder one to make sure both valves were closed as piston 1 is moving towards the top of its stroke. Also when you install the head, leave the spark plugs out so you can at least rotate the engine by hand slowly and know that you won’t have any possible surprises that way also

[ross1]

Align the mark on the cam sprocket with the mark on the head, both valve for #1 should be fully closed. Set #1 piston at top and button 'er up.

[jclausen]

Tdc for cylinder number 1 all valves closed the rockers have play in them, the camshaft moves at 1/2 the speed of the crank, mean the crank has to be spun twice for the camshaft to move one complete turn

[nnastye30]

Align the mark on the cam sprocket with the mark on the head, both valve for #1 should be fully closed. Set #1 piston at top and button 'er up.

So I will be able to tell if its tdc of the power stroke by seeing if both valves are shut on cylinder 1 and 6?(at TDC the cyln 1 and 6 are all the way up) So by basically seeing if the valves are shut while the piston is all the way up?

[nnastye30]

I have the block set to TDC. It has not moved since i removed the head. the issue is telling if the head is at TDC, i took it to the machine shop and it was moved off of TDC and they are not sure how to set it back.
I will be sure to turn the motor over manually and see if theres any interference
but is there no other way to see where TDC is other that by playing it by eye?

Thanks for the help

[msservices]

Are you putting this together without a book/manual?

[superj]

Power stroke doesn't matter to the block side of the engine, it only has up or down. Power stroke matters to the head.

The best way is to put block at up position, as you have, than align the valves closed on number one set of valves and check of the alignment mark looks fairly close to where it would be pointing while on the engine. Than carefully set it in place and see if your marks are correct. Don't tighten anything down or put the timing belt on till you get the marks fairly correct. Than you can torque the head down and do the rest of the assembly. It's not going to get destroyed if it's off a little when you first out it on but just don't tighten it down and make the adjustments till the marks look good.

You will be good to go than. You can move the rimming marks a little bit with no belt on if you are careful. You won't be able to turn it alot of the valves will stop you but if you turn by hand, you will know when they touch and then you can turn the crank by hand a little and back and forth till the marks are lined up..

Building an engine is a feel type thing. Like using a micrometer or a feeler gauge.

[nnastye30]

Are you putting this together without a book/manual?

I have been using a general service manual i found online, is very detailed but not very detailed about what I am trying to do

Do you have any suggestions for a detailed engine repair manual?

[nnastye30]

Power stroke doesn't matter to the block side of the engine, it only has up or down. Power stroke matters to the head.

The best way is to put block at up position, as you have, than align the valves closed on number one set of valves and check of the alignment mark looks fairly close to where it would be pointing while on the engine. Than carefully set it in place and see if your marks are correct. Don't tighten anything down or put the timing belt on till you get the marks fairly correct. Than you can torque the head down and do the rest of the assembly. It's not going to get destroyed if it's off a little when you first out it on but just don't tighten it down and make the adjustments till the marks look good.

You will be good to go than. You can move the rimming marks a little bit with no belt on if you are careful. You won't be able to turn it alot of the valves will stop you but if you turn by hand, you will know when they touch and then you can turn the crank by hand a little and back and forth till the marks are lined up..

Building an engine is a feel type thing. Like using a micrometer or a feeler gauge.

When you say "seeing if the marks are correct" are you referring to the cam gear pulley arrow aligning on the head? Are you referring to the TDC marks? Also, what are rimming marks?

I am planning on getting the valves to align based on what i see on the block. So, I see that cyln. 1 and 6 are both all the way up, so i will make sure that the valves are closed on both cyln 1 and 6 on the head when i have the camgear pointed at TDC. then i will pull the spark plugs to remove any compression and the rotate the motor by hand and see if there is any interference. Is that a good plan?

Thank you for the help i appreciate it

[superj]

let me see if i can find the timing instructions online.

- - - Updated - - -

https://www.pelicanparts.com/bmw/tec...iming-Belt.htm

there it is, good ol' pelican parts still has the instructions for the timing belt change with pictures