how do I find, TDC on piston #1 for timing?

[Tricky]

I have worked out all of the bugs with a stripped key on the crank, now the task of setting in the timing belt. On my 1992 legacy, how do I find top dead center on piston #1?

the timing belt has been removed and the crank has been turned by hand (in order to fix the stripped out key) and all of the pulleys have been turned.

How do I go about finding tdc, and any suggestions on making the timing belt installation would be GREATLY appreciated. This site is great, you all are knowledgeable car folks!!

 

thank you.

 

P.

[Legacy777]

here is the factory procedure for doing the t-belt

 

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt1.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt2.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt3.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt4.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt5.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt6.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt7.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/Timing_belt8.jpg

 

 

as for finding TDC...I'm pretty sure all you need to do is align the marks on the cam pullies to the plastic cover, and the mark on the crank sprocket in the back to the alignment mark.

[ejlain]

here is the factory procedure for doing the t-belt

 

WOW! Those scans were really good Josh. I might actually take on the t-belt job myself after looking at those.

 

Thanks for the post.

 

Ed

[Tricky]

Thanks for the diagrams...this helps.

 

but before any of this..I have to ensure piston #1 is tdc..or nothign will work.

I can NOT seem to find out how to do this??

[jimmyberka]

the #1 piston is not suppose to be on TDC when you put the timing belt back on. If all the arrows on the pulleys and belts are lined up as stated in the procedure, and you have the correct tooth spacing between each crank arrow, everything will work out. THEN, once you have it all together, you can use the mark on your crankshaft pully to show you where TDC is.

[cookie]

spark plug. Since you probably don't have a degree wheel and a dial indicator take a piece of wire, coat hanger will do, and put it in the plug hole to feel the piston top.

When it is as high as it goes you are on TDC.

You can use this to double check your marks but when you time it up follow the procedure in the link above exactly.

[tcspeer]

T.D.C. must have the # 1 piston at the top on the compression stroke. Use a compression gauge to tell. It will also be at the top on the exhaust stroke but that is not right. When you see the gauge start to show compression then line your mark up.

[99obw]

Jimmyberka is correct.

 

My way of thinking about it is that after the timing belt is removed, every rotation of the crank is potentially the compression stroke for #1. Same with the cam. Every time the marks line up the thing is correctly timed. Just line up the marks.

[tcspeer]

From Haynes

Top Dead Center is the highest point in the cylinder that each piston reachest as it travels up the cyclinder bore. Each piston reaches TDC on the compression stroke and the exhaust stroke, but TDC generally refers to piston position on the compression stroke.

More from Haynes

Note: Because either cylinders 1 or 2 could be at TDC position when the timing marks are aligned, it is important not to mistake the wrong cylinder at the TDC position; make sure compression is apparent at the number one cylinder as the crankshaft is rotated and the notch on the pully is nearing the timing scale.

[99obw]

From Haynes

More from Haynes

Note: Because either cylinders 1 or 2 could be at TDC position when the timing marks are aligned, it is important not to mistake the wrong cylinder at the TDC position; make sure compression is apparent at the number one cylinder as the crankshaft is rotated and the notch on the pully is nearing the timing scale.

Yes, that is true, until the timing belt is removed and the cams and crank are turning independently. It's only because of the 2:1 crank:cam ratio that the marks being lined up can indicate one of two possible cylinders is at TDC.

[tcspeer]

99obw

 

you may be right I am no expert I have only done two timing belts in my life. But each time that mark is lined up either the #1 or # 2piston is at the top, I would at least think you would have to go back to what cookie said and at least make sure the # 1 was at the top. If you are right then I have been going to lots of extra work.

[cookie]

stroke. You are setting where the compression stroke will be when you set your cams.

This will just show you that you have your tdc mark in the right place. This can get tricky on certain engines that require a mark on the flywheel to trigger the ignition as you have to use the stroke that has the number one piston up and the flywheel trigger aligned.

If I recall Subaru is using the crank pulley for a trigger so if you have number one up and test fit the pulley it should show tdc. Then you can fasten it up and move everything to the correct spot and put on your belt or belts as the case may be.

If you were just prepareing a running engine to change the belt you could use the old paper towel bit in the plug hole and bump it over on the starter till it blows out the paper and there is your compression stroke.

There are several ways to do this.

[tcspeer]

you guys are right their is no compression without belt on cams, I wonder why Haynes makes such a big issue out of getting the # 1 piston up on the compression stroke for timing belt change? I had always thought it had something to do with the position sensors. Thanks you have taught me something.

[subyroo]

I have never done a boxer cam belt or even seen one to be able to quote anything about them.

 

However, if the "boxer" is anything like the Nissan RB30E then TDC will play a very important part indeed.

There was a mark on the belt for aligning it to the crank pulley and then there was a directional arrow as well then there were 55 teeth between that and the next mark on the camshaft pulley, one tooth either way and it ran like a dog.

It would idle great but it had no guts when you drove it.

 

So I can see the point Haynes are making if these engines work on the same principle of alignment.

[99obw]

I think we are talking about two different scenarios here.

 

1. You are going to take the belt off. Haynes advises to align the engine to #1 TDC. This is good advice. Most manuals recommend the same thing when removing timing components, regardless of engine design. I do this. I use a compression tester in #1 to bring it to TDC. Doing this may be more important on interference engines where you want to be very sure of where the pistons and valves are in relation to each other.

 

2. The belt has been taken off and the crank and cams have been turned all willy nilly. This is what I was trying to describe in my previous posts.

[cookie]

just back from the machineist is a bit more of a pain than a service cam gear, chain, or belt job.

Follow the book exactly if you are just changing a belt on a running engine and find TDC on the compression stroke on any accepted method.

Then follow the procedure for that engine exactly.

This poor guy has had his crank keyway strip and should check to make sure his TDC is really TDC. All timing usually follows from TDC.

When you blueprint an engine the first thing you do is set an accurate TDC with the piston, rod, and crank combination you are useing.

Then you go on to set your cams where you want them. Frankly there are whole books on this and it would waste a lot of bandwidth to go into it here.

If you are doing a job like this for the first time it would be best to tear down exactly like the manual says to prevent any valve damage.

[NOMAD327]

A simple point here is that the crank turns twice for every one cam rotation. The cam doesn't care which rotation the crank is on, because it will line up on one rotation then 180 degrees out every other rotation. That is to say, if you line the cam up with # 1 piston at top dead center and install the belt, then turn the crank one full revolution, everything will now line up perfectly with #2 at top dead center. (This is valve timing, both #1 & 2 cylinders are at crank top dead center at the same time) First is top of power stroke on # 1, second time is top of intake stroke on # 1. The requirement for #1 stroke TDC is for firing spark plugs when there is a distributor type ignition. If you have a crank trigger ignition, the plugs fire on every revolution, wasting a spark on the exhaust stroke, so the #1 TDC position requirement is even becoming obsolete when talking spark timing. In any case, crank to cam relationship is set using the timing marks and on the older models we are talking about, there isn't a problem with valve interference. If I need to find the TDC on #1, I do it as follows. The timing belt needs to be installed with timing marks aligned, and the motor is turned in the normal direction. One method is to turn the engine in the forward direction with your finger partly in the spark plug hole and when you start to feel air blowing out, it's on it’s compression stroke. Continue slowly until the timing marks line up and it's at TDC of the power stroke. (This is when the spark plug will fire roughly and you would set a distributor rotor at this point). If the valvetrain is exposed it's even easier, turn the engine in the correct direction until the cylinder opposite in firing order (#2) has it's intake valve just start to move. The crank timing mark will now be very near TDC. With #2 cylinder at the top of it's intake stoke, the opposite cylinder (#1) is at the top of it’s power stroke and it’s at the correct spot to set rough ignition timing. Once rough timing is set, the motor will be capable of running and fine timing can be set using a timing light. (This is for motors with a distributor). If the haynes manual is having you check these things without need, it may be that it covers models other than yours that still have a distributor.

 

[Legacy777]

If you are just changing the t-belt.....there's absolutely no need to TDC the engine.....just get all the alignment marks on the cam & crank lined up and your golden. TRUST ME! I just did this job, and was quite surprised at how easy it was. You do need to make sure you pick the right marks and align them to the plastic covers. But other then that. It's simple.

[cookie]

my understanding is that if you line up all the marks you are golden.

Most engines are not set up with the multi marks and you may see Subies with non standard belts or belts with marks that are worn off.

A timing belt is only a belt of a certain length and width. A genuine Subaru belt I have seen has marks that make it easy for you. Thank you Subaru!!!

Not everybody is this kind.

I saw one in New Zealand with no marks on the belt and the dang thing was so dirty we had a heck of job spotting where to put the belt under the light of a shaky flashlight.

Good old non interferance 2.2s, we finally got it running and no worse for wear.

[bubaroo]

I have my head off my 2.2 and the timing marks almost threw me at first until I thought about it.On the cam pulleys there is a notch that is to be lined up with the notch in the rear timing cover when installing the belt.There is a mark on the crank gear that is to the rear of the gear and it should be lined up with the mark on the back of the cover also.Now when I had all this lined up and pulled everything apart to do my valve replacement I noticed that my piston on the #1 cylinder wasn't at TDC!I thought oh #$%@ Haynes has done it to me again.Well I saw these arrows on the cam pulleys and I turned my engine to bring these into line with the notches on the cover and my #1 piston was at TDC.Anyway this really didn't matter for me in the scheme of things because I could turn my crank gear to line up the mark(which is not TDC by the way) and then set each cam pulley to their respective marks and install my new belt and all will be good.So I think if you need to find TDC on the #1 piston compression stroke just line up the arrows on the pulleys with the notches on the rear timing cover and you should be good.I'm simply stating what I observed on my '90 EJ22 so someone may want to investigate this further.I'll do a check by using my compression guage when I get my head back on and check the arrows to see what lines up.I'll post the results here.

[Tiny Clark]

I agree with jimmy and 99, the cam is what makes the stroke a compression or exhaust type.

 

There should be no resistance on the cam sprocket for the #1 side (it should move freely), since the valves are all closed in the compression stroke. The other cam sprocket should be a pain in the rump roast to get the marks lined up, as the valve springs are being compressed.

[Tcrowe3]

Cookie,

I joined USMB Forum several months ago because of the need to replace a CV Axle, The CV Axle was a no brainer. But I also had some cooling issues that were out of "my norm" meaning that all the usual stuff was not resolving the problem and knew that I was going to have to go after the Water Pump. So I was just doing the reading about replacing Timing Belt, Water Pump, and what not. I must say; I'm not some "Mech-Head", I'm more of a "Back-Yard Mech" I do have several things going for me such as several Mechanical Engineering Degrees and have always been good with my hands...even with autos. With all that said; during my investigating of the finding the "best" Timing Belt Kit and Water Pump I came across your post about finding TDC with a coat hanger. I kept it in mind because of the constant warning about making sure of this in many books and posts across several forum boards because of this engine being an "Interference Type".

 

Well Cookie, Guess what.... After all was apart and I began the process of putting on the new timing belt I discovered that cam pulleys were all "f"d up and the marks were never going to all line up unless I went thru the process of finding TDC on #1 AND ,,,I Do mean AND!!!...and then making sure that #2 was were it was suppose to be. Pulling the spark plugs and using your coat hanger trick worked!

 

After turning the Crank Sprocket to align notches and arrows as shown across the mountain of literature that I have found concerning this engine, I found TDC on #1 (using a Coat Hanger in SP port #1) rising it to the top (coat hanger sticking out the farthest), seeing that the notches on the cam pulley did align with the engine. I then went to SP port #2 with my coat hanger and did a check on that to ensure that it was at the bottom of stroke (coat hanger sticking in the farthest), at the preceding moment of start rise, again the notches all aligned as they should. Then as a triple test I pulled Plugs #3 & #4 and compared the positions on those with each other and #1 & #2 as well. I Know the last part was a bit dumb cuz the cam shaft can only do what it does...But I'm an Engineer and over checking is just part of who I am. I'm Not OCD..I'm An Engineer! LOL !!

 

Cookie the long and short of all this is I wanted to Say Thank You!!!! Your Info was correct, logical common sense stuff and very helpful. Everything is back together and running one hell of a lot better as of day 1.5.

 

Summary:

I believe that the problem that I encountered and others have posted, is a result of timing belt stretch. What I mean by that is this; If the person replacing the timing belt only does the paint pen method of marking across belt to cam pulley from notch on engine it will work for awhile, IF the cams have not already started to walk out of time because of belt stretch which will have a appreciating effect every time the belt is replace using the paint pen method. But thinking about what I encountered leads me to believe, that if your replacing the timing belt for let me say more than the 2nd time and the Mech used the Paint pen method before, (which was clearly visible in my case) the cams have already stated to walk forward. I have +174,750 miles on my Forester, and have the anal service records from the previous owner showing that the last time the timing belt was replaced was at +/- 90,000 miles. So In my estimation of the books all stating "FIND TDC" its worth the time with this type of engine.