Hello everyone,
I installed a new timing belt on my 245 but I wanted to verify my setup by manually rotating the crankshaft until I could see again all aligned features.
I mean: belt marking, pulley marking and engine marking all aligned on all three shafts.
It seems I did something wrong or it takes many full rotations before you see the same pattern again? So far it does not seem to show the original alignment but I did not perform more than, maybe, 12 full rotations.

Does anyone know the answer to this question below? Assuming the three pulleys line up perfectly to belt and engine marks during install.
How many full rotation of the crankshaft does it take to reproduce the original alignment between belt marking, pulley marking and engine marking?

Thanks for your help.

Hi,

Boy you sure brought out the brainy techno people by asking that question.
Looks like you got good answers too.
Don know what I would do with that information though except to let it try to absorb between my ears.
It sure does make one appreciate all the brain twirling to get it thought through. 👴 I bet a few of us are hairless because of things like that in our pasts or for most, it’s just El naturaL.

Yep, the lines are use for reference to confirm that you have all the “slack out” between the two upper marks.
The intermediate gear for the distributor is important in a sense that there is a parallax problem involved with sighting the 3 O’ clock position.
I have to use a mirror down there to get a straight on view.

The crankshaft mark is another situation that involves the line being projected on around to the tooth it is to engage on the crankshaft. As the belt is not flexible enough to lay over to it while all of the rest it laying up around their respective sprockets.
I find that the line is about two or three notches higher up and needs to be counted over to fill that tooth.

Like everyone is saying the “proof to the puddings taste” is the final rolling it over “clockwise.”
You have to get all “three marks” coming around repeatedly on the number ones Top Dead Center mark.

That last part, by Art, about every 25 seconds @ idle even sort of surprises me.
I thought more about it years ago and @ road speeds as how it would be zinging even faster.
Imagine four or five times faster while climbing a grade.
Things are sure working out there!

Makes you wonder just how long does a drop of gasoline get to be completely combusted or its power extracted.
Might explain some inefficient processing for a century long life of these ICE, machines.

Our older engines are slower, but then our pistons do not vibrate but will actually move up and down!🤫
Inertia of mass and explosions per revolution equals power output. Disregard energy values.
No wonders were about finding a compromise, as finally, there’s the variety of speeds offered in transmissions used with todays smaller lighter engines.

Valve floating with an interference engine has always seem dangerous to me.
Let alone varying the timing of them early or later.
That’s a maintenance of gadgety being put on the front street edge silently to the consumers dollars.
Bring More Wages or have an eccentric relative.
😵‍💫 if the machine catching a cold, toss in requisition slip, instead of a shop rag.

The electronic governance idea doesn’t stop the mechanical aspects of what’s really happening.
Gives a “red line terminology” some variations of meaning!

See where thinking over some technicalities can place you being a 200 Brickster?

Thanks for the read..


Phil

Thought I'd stick my 2 cents in since I just replaced the timing belt on a 740. The owner ordered a Continental belt kit as I'd asked. I found the marks on this belt confusing as the stripes were not aligned perfectly to the teeth. I knew I had the marks on the gears aligned with their corresponding marks but it was disturbing to not also see perfectly aligned stripes. Start-up told me all was well. - Dave

I'm sorry that I do not know the specific answer, but want to mention that the belt position is irrelevant. The important consideration is that the counter balancer and cam sprockets are in correct sync with the crank. The former sprockets are both 38 tooth, and the crank is 19 (I think I have those counts right, but you can verify on your engine), providing a 1:2 ratio of the drive vs driven. You can figure out where the belt figures in mathematically, but again, it's irrelevant. The important consideration is that the upper two hit their alignment marks every other time the lower one hits its mark. By mark, I'm referring to the factory marks on the sprockets and inner timing cover, not the marks you may have put on the belt (I've personally never done this).

It used to be a common question on this board 20 years ago. Your tooth counts are correct. Add the number of teeth on the belt, 123, and you have the data needed to get the answer.

The timing belt is 123x3/8" (46.125") in length.

The installation marks are at tooth 44 for the I-shaft and 71 for the crank with respect to 0 being the cam's mark.

The marks return to the installation position
...every 123 cam revs
...every 38 belt revs
...every 246 crank revs

Or about every 25 seconds at idle.

They're just marks for installation.


--
Art Benstein near Baltimore

"Our A students become professors. Our B students go to law school. Our C students rule the world." - Henry Rosovsky

Wow, you did the math, Art, I'm impressed, but expected nothing less. I once thought about thinking it through a few years ago but figured who cares, too much brain power and I'd have to find sprockets to count. I had guessed hundreds, so not worth the effort to turn by hand.

In addition to making installation simpler (if you don't know how to wrap the belt), the belt marks are also good for verifying you've bought the right belt, albeit you may need to flip it over to check. B230F timing belts are consistent over the years other than chisel tooth vs the later round tooth, so odds are good you'll get the right belt unless there's a bin mixup. B234F belts on the other hand, there's two not far off lengths for the cam belt, those with the manual tensioner (similar to the B230F tensioners) and the later B234Fs using a hydraulic auto tensioner. Rather than count the teeth, the belt marks are the easiest verification. In parts listings it says auto and manual, making people think it's the transmission. It was a relatively rare engine and even the shops and dealer parts got confused.

Thinking of B234F timing belts, interference engines like the B234F should use auto tensioners. Probably half, if not more, of the bad B234F reputation for broken belts and likely bent valves, damaged head or damaged pistons, were those having a manual tensioner, either poorly set initially (there was a spec and a special Volvo-only belt gauge) and especially those who didn't take it back to the shop for readjustment at 500-1000 miles. Some early catastrophic failures were the intermediate sprocket (bell shaped oil pump pulley) either fracturing or its standard grade bolt sheering, both likely from over-tension. Otherwise, it was really a nice engine, especially on the highway, similar to turbo horsepower without a hint of lag and better gas mileage. The mated AW72L trans, a differently geared AW71L, was not ideal. They raised the gear ratio in 1st and 2nd to get around the weaker low rpm torque until the engine could start to breathe, leaving a large gap to 3rd. They overdid 1st, you'd easily spin your wheels leaving a stop sign in the rain. A five speed trans would have been more appropriate. I almost scored a dirt cheap 940 GLE B234F a few months back, body and interior excellent, if nothing else worth the price of the leather seats to replace my worn ones. Advertised on Marketplace with persistent rough running the owner said he didn't have time to fix as he needed the cash, I knew it had to be a bent valve. I responded that evening and the guy had 70 prior offers, so no luck. Odds are none suspected a bent valve and would soon learn it was going to be a diffult and expensive fix and if the head was damaged then a writeoff as you can't find a good B234F head anywhere these days. I should have asked to give my contact to the buyer in case it didn't work out -I could then make a low ball offer as a parts car.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Art--thanks for the actual answer to the OP's question. I didn't broach that bit because I didn't want to admit the math was a bit beyond me, especially first thing in the AM :-).

-Wilson

Wilson, I'm with you. The only mental challenge here was to remember where I'd put my notes from 2003:





Failing that, I would have left the thread alone :)


--
Art Benstein near Baltimore

Did you know actor Raymond Burr had a brother who was a lumberjack? His name was Tim.

Hi everyone and thank you so much for all your replies.
I am of course quite amazed by Art's answer. I think I have sent an engineering exam question out there. I would say most mech eng students would not get the right answer to that question.
As it is Art's habit he never fails answering technical questions with accuracy and knowledge.
Art,
You should start a business as auto maker. I would love to get a new 245!

Yeah, a mechanic friend of mine told me it is an academical question at best as it is not very practical to repeat the original belt marking locations with the sprockets by rotating the crankshaft.
He told me the belt markings are for install purpose only.
And yes I got it: The critical point is to make sure that the sprockets return to the TDC proper marking from the engine side after two crankshaft rotations.

Still really impressed by all answers received after just a few hours.
You all are fantastic people.

Richard B