Cambelt adjustment..how often after replacement?

[DaveyT]

Hi all,
what’s ppls experience here please? 

 I fitted a new belt, overhauled the tensioner, and reset to 110hz, but now have a little flutter between dizzy and intake cam at around 1900-2000rpm. As you will know, she is up for sale, but I’ve been enjoying  a few shakedown miles, now about 80 since initial belt setting. 

Genuine, standard belt from Lotusbits, current tension 108hz. Is this normal, and how often should I be making the adjustments? Thanks, 
Dave

[ekwan]

Should not need adjustment over its working lifetime. 

[DaveyT]

Thx Eric, So no initial stretch to be expected?

maybe my iphone frequency checks need confirming?

@Gis, i know you went thro this with a gates belt. Any suggestions? Ambient here about 12degreesC..

[ekwan]

There will be a little stretch on initial use, but should not be an issue with needing to recheck belt tension. I have always used a Facom belt tool and never had an issue. 

[Gis]

2 hours ago, DaveyT said:

i know you went thro this with a gates belt. Any suggestions? Ambient here about 12degreesC..

People are usually guarded with advice when it comes to these issues since there are many variables (type of belt, ambient temp, condition of tensioner etc). For me, If it flutters, I’d tighten it. I think every belt stretches to some degree after initial install. I’d go a little at the time (1/4 - 1/2 turn for example) measure the frequency and document it. You’ll probably notice that the flutter will move up the rpm range with each tightening itineration until it disappears. If it whines when the engine is at operating temp, you’re too far and you can roll it back. If you do this systematically and in small steps, you’ll be safe. 

[ekwan]

I'd use a proper tensioner tool and relegate all worries to the back of my mind. No guess work.

[DaveyT]

Many on here now use tuner apps of various types and tension by frequency, with no reported issues.

I’ll Probably go gis’ route  initially, but if the frequency then appears way out, I’ll run her down to Swlc or SJ.

will download another tuner app first though.

thanks both, thats todays job sorted👍🏻😀

[Gis]

Since a proper borroughs gage is unobtainium here, I apply the gates carbon drive app. I find it useful, consistent and reliable. I applied the krikit gauge as a backup 

[sailorbob]

From what has been posted before, for a new trapezoidal belt the frequency should be between 105 and 115 Hz when checked between the auxiliary and inlet cam pulleys at an ambient temperature of 15 to 25 deg C. Lotus recommend the tension should be checked again after 500 miles.

A used belt is possibly between 85 and 105 Hz based upon Gates information.

[ekwan]

https://www.fac18.eu/fi-en/categorie/automotive/timing-pulleys-belts/pulleys-sprockets-belts/belt-tension-testing/produit/multi-make-electronic-belt-tension-meter

This is what I've been using.

 

1 hour ago, Gis said:

Since a proper borroughs gage is unobtainium here, I apply the gates carbon drive app. I find it useful, consistent and reliable. I applied the krikit gauge as a backup 

I believe the Gates Krikit tools are only for V and Poly V belts only.

Edited December 11, 2019 by ekwan

[Clive59]

This is the Gates app, works very well.

https://play.google.com/store/apps/details?id=com.gates.carbondrivecalculator

 

[DaveyT]

Thanks @Clive59.

downloaded it this morning. Last time I checked, they didn’t do an ios version, so I used a guitar tuner app.

all set now at 115Hz, checked several times, and good results (was down at 104.9 according to Gates app, so would have been lower in higher temps?)

 Maybe a slight flutter on the overrun,  still at 2k ish, but nothing on the way up, so far, far better

[Gis]

2 hours ago, Clive59 said:

This is the Gates app, works very well.

https://play.google.com/store/apps/details?id=com.gates.carbondrivecalculator

 

Yes, it’s the same app I’m using. There is an iOS version Dave. The tension increases on the belt as the engine warms and expands. That’s how the flutter disappears. With a cold engine at startup the flutter is possibly a combination of (too) low tension and harmonics at a certain rpm level. My blue belt still exhibits a very slight flutter at times only in the first few minutes after startup in the 1800-2000 rpm range. I should probably tighten it a tiny bit more, But it’s nothing that really bothers me. I always make it a point to let her idle until the water temp comes up, usually 7-8 minutes before I drive off. Can’t rush the old gal...

[Clive59]

i recently did my cambelt, and when warm was over 150Hz, but duly returned to around 105-110 when cool again.

[Andyww]

On these engines the tension varies a lot with temperature. That was the issue with the very early engines destroying themselves and the spring tensioner having to be hurriedly designed and fitted. The belts became too loose when cold and made worse by developing a "set" when very cold.

 

[JerryS]

Dave I noticed this post on the Lotustalk forum from Tim Engel re crank position for frequency test...

https://www.lotustalk.com/threads/timing-belt-tensioning-with-a-snark.470848/#post-5965838

[ekwan]

On 11/12/2019 at 15:53, sailorbob said:

From what has been posted before, for a new trapezoidal belt the frequency should be between 105 and 115 Hz when checked between the auxiliary and inlet cam pulleys at an ambient temperature of 15 to 25 deg C. Lotus recommend the tension should be checked again after 500 miles.

A used belt is possibly between 85 and 105 Hz based upon Gates information.

Wouldn't the frequency pretty much depend on the "free" length of the belt i.e. the principle of piano strings??

On 11/12/2019 at 23:32, Clive59 said:

i recently did my cambelt, and when warm was over 150Hz, but duly returned to around 105-110 when cool again.

My guess is that the expansion of hot engine components is sufficient to raise centre-centre distances of the rotating components, thereby raising the tension and belt frequency as you'd expect. Lotus recommend an ambient temperature of between 15 - 25 degC and tension taken at 120deg crankshaft, pretty starting off from TDC.

Edited December 13, 2019 by ekwan

[sailorbob]

The frequency of a timing belt depends on the belt's span length, type, weight and tension.

[DaveyT]

Good Night, Eric? 😂😂

 

[gvy]

Just for info's,

We had this topic here. I remember, I went into detail about frequency tension in the past:

 

[Sparky]

If I don't see a cambelt tension topic at least 4 times a year, I get the jitters.

[Andyww]

Its about once a month on Ferrarichat so we get away lightly here. Narrowly beats "what oil is best".

[DaveyT]

26 minutes ago, Sparky said:

If I don't see a cambelt tension topic at least 4 times a year, I get the jitters.

Thats why stickies are so good...or did I miss it?

I do use the search facility before posting, but things always get a little fuzzy after wine o’clock....

[ekwan]

Getting a little stale now. Unfortunately, not looking like it'll go away soon.

[DaveyT]

Highly recommend @gvy’s post above, detailing the calculations and Equivalent Frequencies for belts of different mass. It will enable you to make your own decision on ultimate tension for the belt you are running. (Having made sure the tensioner springs are good)

I hadn’t realised there was so much difference between OEM and the Gates 5146 equivalent currently available

Thanks Geert! 

as an observation....I also noticed that as I increased tension from 104 to 115Hz, the belt started running more centrally on the cam pulleys. At 104, it was pretty much at the front edge, whereas at 115, it sits a good 1mm in.

oh, and what oil should I be using? 😉