1989 740 Timing belt issues

wshytle · Post by **wshytle** » 18 Nov 2011, 06:33

Hello-

I'm new to the forum here and have several questions about my 1989 740 GLE. I recently had some work done on the pcv system and told the mechanic to go ahead and replace the timing belt while he had it. The mechanic (not a volvo mechanic)discovered two belts and that one had not been working for a while. He explained to me the second belt ran a "counter balance shaft" of some sort. He replaced both belts and things were fine for a while. With only a few miles driven the second belt broke again. My question here is what is this second belt and counter balance shaft? The car has been making a whistling noise for years but ran fine. I was told the noise was from the fan belts needing replacing but afterwards the noise remained. I'm now wondering if this noise is coming from the balance shaft system. Can someone give me a short explanation as to what the heck is going on?

Thanks in advance . . . Wayne

Post by **billofdurham** » 18 Nov 2011, 12:27

Welcome to Matthew's Volvo Site.

With a timing, or cam belt, and a balance shaft belt you must have the 16 valve engine. The common or garden 8 valve engine has only the cam belt.

The balance shaft is an eccentric weighted shaft which offsets vibrations in engine designs that are not inherently balanced, that is most four-cylinder in-line engines. It is possible to run with the balance shaft belt removed if the revs are kept down to avoid harmonic vibrations but it really isn't worth the risk. Some people have claimed to have run for years without it but I am very sceptical. If the balance shaft belt has snapped and the engine is still running you are one lucky person. Usually if the balance shaft belt snaps it fouls the cam belt causing it to come off with possible major damage to the engine as the 16 valve engine is an interference engine. This means that if the cam belt snaps the pistons and the valves make contact causing major damage to both.

How did the mechanic determine that the balance shaft belt " had not been working for a while"? Did he check that the balance shaft was able to turn? That seems unlikely as the belt should last 50,000 miles, the recommended change interval for both belts. When the belts have been changed they should be tensioned correctly BUT the tension should be re-checked after 500 miles. To achieve the correct tension for the belts on the 16 valve engine you, or your mechanic, need a Volvo tensioning gauge. There are ways to work round this but I doubt a mechanic inexperienced in Volvo engines would know these.

Time to re-visit your mechanic and ask him what he did. Let us know so we can point you in the right direction.

The car has been making a whistling noise for years but ran fine. I was told the noise was from the fan belts needing replacing but afterwards the noise remained.

Don't confuse the cam belt and balance shaft belt with the 'fan belts'. They are outside the engine running the alternator, power steering and air conditioning. They are V-belts which will whistle as they age and lose tension. The internal belts don't whistle as they are toothed belts. They tend to snap as they age.

Bill.

wshytle · Post by **wshytle** » 18 Nov 2011, 15:48

Hi Bill and thanks for the fast response.

I do have the 16 valve engine. John, the mechanic told me the "pulley" on the balance shaft was defective but allowed the engine to continue running. He simply replaced both belts along with the "pulley" and sent me on my way. I traveled about 45 miles home with no problems except the loss of a muffler. I started back a few days later to get the muffler fixed and the engine died and the dash lit up about 6 miles from my home. I threw it into neutral and coasted to a safe spot to wait for the rollback. When I got there John looked at it and found the shaft belt coming out of the plastic shroud and broken. That's as far as we have gotten. I was thinking that if the balance shaft had a bad "pulley" but allowed me to travel and once the "pulley" was replaced it had to turn a bad balance shaft causing the second breakage. Should I expect the worst? I certainly don't want any bent valves. Also, do you have to pull the engine to replace this balance shaft?

wshytle · Post by **wshytle** » 19 Nov 2011, 06:15

Does every post have to be screened by a moderator? My second post took a day to be posted.

Is there some way to get a picture of the balance shaft? I'd also like to know the level of difficulty in a shaft R&R. I was told by non-volvo mechanics the engine had to be removed and I definitely want to be sure.

Thanks in advance...Wayne

Post by **Ozark Lee** » 19 Nov 2011, 07:43

Wayne,

As a moderator I apologize for the delay in getting your posts approved. We have recently come under some severe spam attacks and new members are "probationary" for their first 4 posts which requires a moderators approval. Beyond that you are golden and your posts will appear without moderation. I can understand your frustration but, trust me, it is even tougher on the moderators to go through every new post and sort things out.

The moderators here are all volunteers - we do our best but we have lives, and broken cars, as well.

...Lee

Post by **billofdurham** » 19 Nov 2011, 12:49

The moderators here are all volunteers - we do our best but we have lives, and broken cars, as well.

And this moderator lives in the UK so there is a time difference to contend with. After your next post you will be OK.

I have no books showing how to remove the balance shaft nor how to do shaft R & R. However, the time allowed by Volvo to remove and install the balance shaft is 2.5 hours, so engine removal would not seem to be necessary. Attached is the only picture I have of the balance shaft.

740 16 valve cam and balance shaft belts..pdf: (109.59 KiB) Downloaded 412 times

Having replaced the pulley and belts I would assume that John checked that the balance shaft was turning when he started the engine. It is not necessary to replace the belt covers to start the engine as the final tensioning should be done with the engine at running temperature. This gives you a good chance to check that all is well with the belts before covering them. One word of warning about tensioning the balance shaft belt. It must NOT be too tight. It should be slightly floppy to stop it whining. If it is too tight it stands a good chance of snapping. I am not saying that John got it wrong but the tension on the balance shaft belt is nowhere near what a good mechanic would expect.

One other caution with this engine. Whenever the cam and balance belts are replaced, 50,000 mile intervals, you should replace the oil pump pulley bolt as they have a tendency to shear off. The old bolt was class 8.8 but this has been replaced by a stronger version which is class 10.9 M10x1.5x30. Although it is stronger it is still recommended that it be changed at cam belt change time.

Bill.

wshytle · Post by **wshytle** » 19 Nov 2011, 15:26

Thanks Lee and Bill for the posting update. Four posts to weed out spam and such sounds fair by all means. I have been involved with several forums and this was a first for me.

That's good news in itself about not having to remove the engine. John, my mechanic is good but he's not a volvo specialist. I'll run what I've learned by him and see how things go this week. Thanks for the schematic you posted too. That will be a help. I'll inform him about the oil pump pulley bolts too. The vehicle has 195K miles BTW and I hope to get many more.

One other thing...I was told by a volvo mechanic that the 16 valve engine has a Porshe head. I've already seen that it has almost as much horsepower as the turbo 740. Is this true? and why was a Porshe head used? I'm just curious.

Thanks again in advance...Wayne

Post by **billofdurham** » 20 Nov 2011, 11:34

One thing, or perhaps that should be two things, I overlooked about the balance shaft - you have two of them, sitting on the exterior of the engine on its left and right. They spin at twice the engine speed and in opposite directions to help cancel out the secondary or rocking forces generated by four-cylinder engines.

As for the head, I haven't heard that it is a Porsche unit but they don't tell me everything.

The only info I have is that it is aluminium alloy. Overall the 16 valve engine gives 39 more hp than the 8 valve delivering 153 @ 5,700rpm. It is fast.

As we try to give you as much info as we can I have found this excellent article on Brickboard. It may help John to become a Volvo mechanic.

BTW giving you that link doesn't mean you can desert Matthew's Volvo Site.

Bill.

wshytle · Post by **wshytle** » 21 Jan 2012, 16:21

Well, I found out the counter balance shaft was broken. It didn't take but two months but it's being fixed by family at a family rate so I don't really mind waiting. They got it back together and found the valves to be messed up.

What can I expect now. Does this mean start looking for another head? I'd like to know a little about what's involved at this point. The counter shaft belt was installed tight with the original fix but I don't know how much that contributed to the problem. I drove the vehicle about 60 miles and all of the sudden it shut down and the dash lights lit up. I threw it in neutral and coasted to a store a short distance. The engine seemed to be under a strain while running but ran rather well until the shut down.

Anyone out there have valve problems following a timing belt issue?

Post by **billofdurham** » 23 Jan 2012, 12:00

The 16 valve engine is an interference engine. When one of the belts stops working the valves and pistons usually hit each other. If this happens at anything more than idle speed it can mean replacing the valves and, depending on the damage, the pistons. I know others will try to shoot me down on this but my son's timing belt snapped at idle speed and there was no damage whatsoever.

You need to strip the engine down to see what is damaged.

Bill.