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Cam Shaft Alignment / Timing Adjustment & Tweaking (not for the faint of heart) 850 1995

First, I want to salute Mark (Rule 308) – Mark YOU ROCK!

Some of you have been following my Front Exhaust Cam Oil Seal saga here, here, and here.

As a quick recap of how that saga comes into play here, I was afraid that I had been off by about a ½ a tooth on the exhaust cam sprocket re-installation, which by virtue of the timing belt, also caused the intake sprocket to move ½ a tooth for the belt to fit. I concluded after a long and careful study of my markings that I must have retarded both cams together by a total of one tooth, and expressed concern about how that might affect my timing, gas mileage etc.
Both Klaus and Mark had given me excellent responses (Thank You again)… but Mark, who is a pro, turned me on to a thread in the RWD forum here where the tweaking and movement of cams is done to play with and “overclock” - if you will – performance. Mark stated that he had not tried it on an 850, but did not see why it would not work… Well, I tried it, and it works – fantastically. Keep in mind that you may have to read that thread and this post a couple of times before it all clicks and makes sense.

I just got my car back together last night, and this upcoming weekend I have about 8 hours worth of driving to do, so I will try and report back then on the overall results, but I can contribute here and now that this method of adjustment ROCKS! My final choice of adjustment (commensurate with the other thread) was with the exhaust bolt advanced by ½ bolt width, and the intake at full advance.

It gives you the freedom to easily adjust and mark your cam positions without removing the timing belt – and without jeopardizing the crashing of pistons and valves. It literally takes about 5 minutes!

Elementarily – The Cam Sprockets mount to the Cam Shafts by a series of 3 10mm Bolts (part #968159 ) The sprockets, however, do not have simple holes that the mounting bolts fit through, but rather slots. This allows for the sprocket to be turned either way a number of teeth or degrees WITHOUT moving the Cam Shaft. The presumption made in the other thread is that the limitations of the slotting were determined by what variations/ranges would safely prevent the pistons and valves from crashing – in other words, Volvo used a failsafe method and slotted the sprockets for adjustment, but did not slot so far that you could possibly go to a position where the valves and pistons would collide. THAT IS THE PRESUMPTION MADE, and in my disclaimer, I will tell you what range I personally tested.
OK, with that mentioned, open the post here in a new window and read that, then come back, and I will give you some tips.

First, let me make this disclaimer; As with the post here, it seems that the factory setting for the cam sprockets is with the bolts all dead center in the slotting. That was the case for my 850 at least… When I started, because I had mismounted upon re-installation, my exhaust cam was retarded by ½ a bolt width in the slotting, while my intake cam was dead center. I did not want to chance the crashing of pistons and valves, so my initial testing was to adjust and then crank the engine by hand to make sure there was no interference.

IN ORDER TO ACHIEVE THIS TESTING THOUROUGHLY AND SAFELY;
I actually jacked the car up, put it on stands, removed the front pass side wheel, folded back the plastic inside the fender, pulled off the timing cover, aligned the Crankshaft Marking (as you would for changing the Timing Belt), made my adjustment to the widest range (exhaust retarded ½ bolt width, intake at full advance), removed all my spark plugs (which eliminates the compression – thus making turning the crank by hand a breeze – and clarifying any possible “obstruction” as being something other than compression), and cranked the engine by hand something like 10 revolutions. Again - the greatest range I tested was with the exhaust bolt retarded by ½ a bolt width, and the intake fully advanced. Here there was no crashing… I can not vouch for a greater range, ie retarding the exhaust cam further. That being said, I was able to establish that I could make future adjustments within that range and be assured that no piston/valve damage would be done. In other words, I could be assured that in the future, I would not have to go through an elaborate process to crank the engine by hand in order to test whether adjustments might compromise the valves and pistons SO LONG AS I keep my adjustments within the range I tested.

OK, I had a bit of a scare which brought me to confirm my testing; After cranking by hand, I was stoked and put all back together to test drive it. I started the car and it was running VERY rough. That feeling of panic and fear came over me faster than you know what… As I pulled out of the garage, my CEL went off, and I figured I better see what codes it was throwing BEFORE going out for a test drive. I was surprised to see that it came back with FIVE different codes (543,454,545,554,521). Almost all of these have to do with the engine misfiring. Of course I cleared the codes. I went back and checked my re-installation of the plugs and wires, and all seemed fine. Now, WITHOUT JACKING UP THE CAR OR CRANKING BY HAND, I moved the Intake Cam (2 minutes if that) back to it’s original position (dead center)… I started the car, and it was still rough. I went back and moved the exhaust cam back to it’s original position (dead center)… I started the car and still, just as rough. Upon closer examination I found that in a couple of the plug wires, the actual metal at the end of the wire, which is supposed to clamp onto the plug had worked it’s way up the tube, and therefore was not actually connecting to the plug although the tube was fully inserted. I took a few minutes to go through each and every plug wire and get those suckers pushed all the way down… I re-positioned the cams to my tweaked setting (exhaust retarded ½ bolt width, intake at full advance), and started the car…. Purrrrrrr!

Dude!, I was so stoked. I took the car out on a test drive and she just hummed right along – smooth as a babies cheek! As I stated, I will be doing more testing of performance and mpg in the upcoming weekend, but this process has proven to me that you can play with your cam adjustment with very little time and effort.
In order to align your Cams, the Haynes manual directs one to do all the front cam dismantling, and to even dismantle the rear in order to align the rear cam “slots” using a special tool that would cost $600 from Volvo, or you can fabricate your own – either way, there is a ton of work, and the expense for new rear seals, etc. THIS process gives you a methodology that can be accomplished in 5 minutes safely, without any added expense. It provides that if your bolts are dead center in the cam sprocket slots – your slots in the rear will be lined up… and that even if there is the slightest of offset, it would not be noticeable or measurable – and certainly would not justify the cost, time and effort the Haynes recommended process calls for.


TIPS –


  • 1. Before doing anything, lay down a paint strip or some other sort of marking that will indicate exactly where the Cam Shaft aligns with the Cam Sprocket in it’s original position… Do this with a very fine marker so that you can be precise – the more fine, the more precise. FOR SAFETY SAKE, mark the exhaust cam differently than the intake by either pattern or color… this way if there is ever a time in the future where you have both sprockets off at the same time for any reason, you will not get them confused.


  • 2. You do not have to fully remove a bolt to see where the hole resides in relation to the slot! The other post has a picture of this, and hence I did the same. But I found that if you extract just one of your three bolts enough to see the slot, the bolt itself will give you the relation of alignment the moment you see the slot. If you want to add a mark, you could then mark the slot point at which the center of that bolt is protruding…. Keep that one bolt extended far enough to see the slot, but not more than necessary. This will give you the leverage you may need to move the cam, while still offering the bolt to slot relationship appearance as the measure of alignment/adjustment/positioning. See the pictures below for this.


  • 3. I recommend having and or using new bolts on the cam sprockets – At least having them on hand in the event there is a problem since they are only like .88 cents a piece (part#) When I went to remove the old ones (remember I was replacing an oil seal), the bolt heads got a little compromised. The torque on is only 15 pounds, but I had to use a prying device to get the old ones off, and a couple of the heads got rounded corners in the process. I recommend having spares, and should a bolt head get compromised, replace it, BUT DON’T REMOVE MORE THAN ONE BOLT AT A TIME if just doing this adjustment… should you remove more than one bolt, the sprocket could possibly swivel and you might find that you have to go through the elaborate process of removing the timing belt and tensioner and all just to get the sprocket back in place.


  • 4. PAY CLOSE ATTENTION TO TORQUING! The last thing you want to do is to strip out the threading in your cam. Again, the recommended torque is only 15 pounds for installation. If you do not have a torque wrench – the mode of the day is “better safe than sorry”. Theoretically, in the worst case scenario, if the bolts mounting the sprocket are not tight enough, they might give, and the sprocket move, but no further than slotted, and due to the failsafe, your pistons and valves will not crash. ON THE OTHER HAND, if you strip a bolt, you will be left having to settle for 2 mounting bolts, or going through elaborate expense and time and trouble to replace your cam shaft.
    The bottom line is that if this is something that you might play with, (and just in what I did, I tightened, untightened and retightened the sets on at least 3 or 4 different occasions each), then torquing is important or you might accumulate undue stress leading to failure.


A NOTE ABOUT THE FOLLOWING PICTURES;
Once again, I can not post multiple pix on a single message, so I will have to create 6 replies to post all pics; In order to see all the pics, I recommend “expanding the thread”.

First of all, these were all taken during that “5 minute” adjustment period. Therefore components like the coolant reservoir bottle were not removed and I could not get pictures centered on the cams like I did in my other threads or as those did in the RWD section.

Also, LOL, you will see my cam sprockets are all marked up! ALL the red markings pre-existed my work, and I used my own markings for my own reference. In retrospect, I now have a better understanding, and would do it differently. Personally, I opted to number the bolts and their respective alignment positions on the sprocket. Should I ever remove the sprockets, I would know which bolts match to which slots – which really might not make a diff, but by using continual numbers – I am assured which sprocket fits on which cam.

Make sure you read the description to see what the purpose of each picture is for.
Click on the link entitled “Figure___” to get a larger full size image.

Cheers!

--
1995 850T Wagon 120k






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New Cam Shaft Alignment / Timing Adjustment & Tweaking (not for the faint of heart) [850][1995]
posted by  bhs82  on Tue May 10 08:44 CST 2005 >


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