Home 
Home Search search Menu menu Not logged in - Login | Register
> Jensen Healey & Jensen GT Tech > Engine & Transmission > Cam belt tension/ tensioner

 Moderated by: Greg Fletcher
New Topic Reply Printer Friendly
Cam belt tension/ tensioner  Rating:  Rating
AuthorPost
 Posted: 07-17-2005 04:52 pm
  PM Quote Reply
1st Post
Dan (Florida)
Member
 

Joined: 03-16-2005
Location: Ormond Beach, Florida USA
Posts: 97
Status: 
Offline
I put new cam belt idler bearings in  about six months ago and the new bearings are now  whining and must be replaced.  I guess I got the belt tension a little too tight according to what the book says. I don't have a belt tension tension gauge and was wondering how much the upper part of the belt could be moved when the belt is at propper tension.  All of the pulleys are worn and it requires almost full adjustment on the idler pulley to get the belt tight. Those last few degrees on the idler pulley must put a tremendous load on the belt and idler bearings, or I just got a really cheap set of bearings.  It takes (2)  #6005 2RS  bearings  (popular used as front wheel bearings in some jap dirt bikes).     Any better experiences with this bearing set?

Also, is the belt tensioner idler pulley supposed to be slightly rounded, or is mine worn out?     Nothing would surprise me here.

I also wonder how far a camshaft belt pulley can wear before  the reduced diameter of the pulley  becomes a problem  belt teeth or not??

Thanks in advance

Dan

Back To Top PM Quote Reply  

 Posted: 07-17-2005 06:16 pm
  PM Quote Reply
2nd Post
Mark Rosenbaum
Member


Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
Status: 
Offline
Sometimes the bearings are still good and the whine is due to the belt becoming resonant due to tension changes as it ages.  I've had good luck by (a) setting belt tension so that it's possible to manually twist the belt between exhaust and crank by 45^, and if it whines at that tension, gradually reducing tension a little bit at a time until either the whine stops or the belt can be twisted more than 90^.

All the idler pulleys I've seen are slightly crowned, i.e. the center of the pulley has a slightly larger diameter than either edge.  As I understand it, this makes it less likely for a belt to walk off the pulley, and avoids the expense and weight of using flanges.

As I understand things, wear in the cam gears causes slight alterations to cam timing with respect to the crank and between the two cams.  This is due to changing the points at which the belt contacts the gear teeth, not changes in gear diameter.  It's not really a problem unless the wear rate of the timing belt becomes absurdly high, or belt tension drops so low that the belt can jump teeth.  This is a good thing, as the last time I checked, new cam gears from Delta were US $110 each.

 

Back To Top PM Quote Reply

 Posted: 07-18-2005 01:26 pm
  PM Quote Reply
3rd Post
Dan (Florida)
Member
 

Joined: 03-16-2005
Location: Ormond Beach, Florida USA
Posts: 97
Status: 
Offline
Once again, thanks for the info, always appreciated.

ps   Hope hurricane Emily saves a little rain for that part of the country. Sounds kind of warm.

Dan

Back To Top PM Quote Reply  

 Posted: 07-22-2005 01:29 am
  PM Quote Reply
4th Post
Dan (Florida)
Member
 

Joined: 03-16-2005
Location: Ormond Beach, Florida USA
Posts: 97
Status: 
Offline
Well, as a postscript the tensioner bearings have been changed and the whine remains causing a further look at the belt sprockets which are pretty well worn. Delta is on 6 month back order for new ones.  I was wondering if anyone had a spare set laying around they would be willing to part with?  I need all four.  Belts are available locally.  

Thanks in advance

Dan

Back To Top PM Quote Reply

 Posted: 07-22-2005 03:42 pm
  PM Quote Reply
5th Post
Mark Rosenbaum
Member


Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
Status: 
Offline
The crankshaft gear is steel and shouldn't show much if any wear, so I'm curious as to why you'd want to replace it.  For the others, if no individual has a spare set of new gears for sale, perhaps one of the various online Lotus suppliers such as Dave Bean will have some in stock.  Alternately, the cost of a changeover to the newer style timing belt isn't all that much more than replacing all four gears (though one must also modify the engine front cover), so you may wish to investigate that option as well.

Before going to the expense of replacing the timing belt gears, there are a couple of other things you might try:

(1)  Temporarily remove the fan belt to make sure the whine isn't caused by a bad bearing in the water pump or alternator.

(2)  Apply an aerosol belt dressing to the timing belt and see if that stops the noise.  If so, then the cause is slippage between belt and gears.  If that's the case, and if you have access to an abrasive blaster ('bead blaster'), you might try roughing up the contact area of the gears to increase friction.  This may increase belt wear slightly, but belts are cheap compared to the gears.

Re the hurricane, here in Arizona our weather comes from the Pacific, so we get 'monsoons' rather than hurricanes about this time each year.  They're quite mild in comparison.

Back To Top PM Quote Reply  

 Posted: 07-27-2005 05:05 pm
  PM Quote Reply
6th Post
Dan (Florida)
Member
 

Joined: 03-16-2005
Location: Ormond Beach, Florida USA
Posts: 97
Status: 
Offline
Well, as another postscript to the whining cam belt, I finally loosened  the cam belt to a 90 degree twist, which seems mighty loose and the noise went away. You couldn't tell me that this is a proper tension for so important a  belt, but it seems to be doing fine.  Maybe this is the calm before the storm, but it sure is quieter.

Back To Top PM Quote Reply

 Posted: 07-27-2005 10:58 pm
  PM Quote Reply
7th Post
Mark Rosenbaum
Member


Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
Status: 
Offline
My car's PO changed timing belt and tensioner bearings just before I bought the car.  Nonetheless, the engine frequently made whining noises. Some folks kept telling me, "It's a Lotus engine, it's supposed to whine," while others were certain that the whine was quite abnormal.  At that time, I did not find either explanation convincing.

Eventually, through a process of elimination, experimentation, and research, I satisfied myself that the cause of the whine was an over-tight timing belt.  Rather nervously, and expecting a catastrophe at any time, I reduced belt tension in small steps until the whine occurred only occasionally.  At that time I could twist the middle of the exhaust-cam-to-crank span by about 45^.

I drove the car that way for about a year.  By the end of that year, the car was reliable enough to take long drives, and I had become completely fed up with the whine.  I reduced the belt tension in steps until the noise went away entirely.  At that time I could twist the belt by a bit more than 90^.  I tightened the belt slightly until I could turn it just barely 90^.

That was about three years ago.  On rare occasions the engine makes what I can best describe as a faint predecessor-of-a-whine, but nothing more.  I don't take the engine above 6000 rpm very often, but it gets up to 5500 all the time and I have yet to see any problems with the timing belt. 

I've had people with access to a Burroughs belt tension gauge tell me that the one does, usually, get the correct tension when one can twist the belt 45^ to 90^ as described above.  Of course this would depend on the strength of an individual's hands and is very non-scientific.  But it seems to work okay for me.  YMMV, of course.

Back To Top PM Quote Reply  

 Posted: 07-28-2005 11:59 am
  PM Quote Reply
8th Post
Brett Gibson JH5 20497
Member
 

Joined: 03-17-2005
Location: Hilton, New York USA
Posts: 713
Status: 
Offline
I have to agree with Mark, the belt should not whine, even though it is a very important belt and most people would assume tighter is better that is not really the case, if you have noise and your gears are shinney, and the teeth are starting to smooth off, your to tight, I would go with Mark's approach and bit by bit start loosening that puppy up, plus if it's been whining for a long time change the belt and start fresh there cheap enough.

Been there done that ..............       Brett.

Back To Top PM Quote Reply

 Posted: 08-04-2005 06:34 pm
  PM Quote Reply
9th Post
andrewo
Member
 

Joined: 06-01-2005
Location: San Diego, California USA
Posts: 51
Status: 
Offline
Would the tension affect where on the pulley the belt is running? Mine is centered on the cam pulleys, but running toward the back of the dizzy pulley. It does not appear to run off the pulley, but it doesn't seem right. Is it tight, loose, or totally unrelated?

Andrew

Back To Top PM Quote Reply  

 Posted: 08-04-2005 08:02 pm
  PM Quote Reply
10th Post
Mark Rosenbaum
Member


Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532
Status: 
Offline
Normally the belt will sit in the same place on all three gears, though it might be forced back or forward if one or more gears were worn.  But usually what you describe occurs because the big screw holding the distributor gear to the aux. shaft is loose, and the gear is slowly working its way off the engine.  When that's the case, the fix is to tighten the screw to 25 ft-lb (if you believe the specifications in the shop manual) or to 54-56 ft-lb (if you prefer to believe section A52 of the shop manual).  Personally, I use the lower torque and some blue Loctite threadlock.

Back To Top PM Quote Reply

 Posted: 08-05-2005 04:29 pm
  PM Quote Reply
11th Post
Joseph Mazurk
Member
 

Joined: 03-14-2005
Location: Chicago, Illinois USA
Posts: 38
Status: 
Offline
If you are worried about your cam gears, buy the half-moon type from Dave Bean. Sure they are a little expensive but you get a belt that doesn't need to be changed as often and there is less possibility of the gears wearing out. Also, keep in mind when the timing belt (either stock or Dave bean type) is cold it might seem loose but as it warms up the belt does tighten. You can affirm this by checking the tension of your belt before you drive it then check it again right after you park your car.

 

                           Joseph Mazurk

                  very happy with the half-moon setup

                         Chicago, IL

Back To Top PM Quote Reply  

 Posted: 05-29-2006 12:03 am
  PM Quote Reply
12th Post
Joseph Mazurk
Member
 

Joined: 03-14-2005
Location: Chicago, Illinois USA
Posts: 38
Status: 
Offline
On later pondering I figured out that the engine expanded and coaused the belt to become tighter. ofcourse, one might say , doesn't the belt expand too??" it does but at a different rate than the engine. As ststed earlier check the belt when its cold then take your car for a drive and you will notice that both the timing belt and the alternator/water pump belt will be tighter.

                                       joseph mazurk

                                          Chicago, il

 

 

Back To Top PM Quote Reply

 Posted: 05-30-2006 11:31 am
  PM Quote Reply
13th Post
Brett Gibson JH5 20497
Member
 

Joined: 03-17-2005
Location: Hilton, New York USA
Posts: 713
Status: 
Offline
Not to cloud the issue even more but, I have been checking the belt tension with a "belt-tension gauge" and even with the engine cold, it also matters were the belt is in relation to the timing ............. not sure why.

I took a reading of 140lbs at a randon place when the engine shutdown, then aligned the TDC and cams and got a 110lbs reading, which seem's to be a good tension poundage so far.

Back To Top PM Quote Reply  

Current time is 10:01 am  
> Jensen Healey & Jensen GT Tech > Engine & Transmission > Cam belt tension/ tensioner Top




UltraBB 1.172 Copyright © 2007-2011 Data 1 Systems