chassis dynomometer bearing noise

[ivanheow]

hello all ,

im using a sun/maha/snap on , ram 12 .

it was stored under cover for 7 years and i mean a lot of covers ,and kept dry .

after having a little circuit board fun with it , i have it rolling and recording data ,the problem now is ,at around 95 mph , the machine starts making a very loud machine gun rattling noise ,and power on the graphs drops 25 bhp . if you keep it accelerating it stops around 115mph and goes on fine to 125 mph ,then does it again on the way down . i tried it with two different cars ,same dip in the power .

i replaced the woodruff key on the rubber flange joint to the absorber ,because that had loosened and fidgetted outwards ,this made no difference , i located a couple of rumbley bearings on the idler rollers , so this is my next approach , can a bearing cause this though ?

has anyone out there had any similar sort of problems ? the bearings are typical plummer/pillow block 40mm id 75mm od bearing mounts ,with a 135mm foot spacing .


thanks
regards
robert

http://www.youtube.com/user/legrandphromage

 

[ivanheow]

well, after a bit of experimentation ,heres a bit of data in case anyone else has a similar problem ,

the test i did ,was to warm the rollers with a bit of up and down speed, with no load or high speed ,then let them cool for 10min.

taking bearing no1 as outside of the absorber ,then the numbering goes along the driven shaft to the end ,then over to the idler side and back along to the end nearest the retarder .

no.--- cooled ----------timing run to 120mph--------steady 95mph 30secs

1--------18c----------------------28c-------------------------26c
2--------18c----------------------30c-------------------------29c
3--------16c----------------------37c-------------------------30c
4--------15.5c--------------------24c-------------------------28c
5--------15c----------------------18c-------------------------18c
6--------19c----------------------42c-------------------------40c
7--------18c----------------------39c-------------------------40c
8--------18c----------------------36c-------------------------32c
9--------16c----------------------27c-------------------------35c
10-------16c----------------------20c-------------------------21c


temperatures were taken with a infra red gun .

looks a bit radically different bearing to bearing .next experiment when i get back from vancouver ,is to pump in some ep90 ,and see what that does ,it is starting to look like i need a few new bearings though ,maybe moisture condensed in the bearings during its time in storage ,and rusted something ?

regards
robert.

http://www.youtube.com/user/legrandphromage

 

[caoimhin1]

If there was a problem with the bearings, such as corrosion, you would expect the rumbling noise to be present over all speeds. Maybe some resonant frequencies with some other componenents.

 

[BrianE22]

my guess - you're running through a resonance and at resonance there's excessive motion because there's too much bearing clearance.

 

[ivanheow]

thank you ,

do you think that the data from the temp gun , is indicative of specific bearing problems ? or are the temps and timescale insufficient to create a big enough temp to show a failure ?

http://www.youtube.com/user/legrandphromage

 

[Tmoose]

bearing temp is a good indicator of lubrication issues, or preload getting too high, especially if measured real time on a race. "Low speed" lighlty loaded bearings can chew themselves to junk without generating much heat at all. Or, run a really long time with major surface distressescalating slowly.

lacking a vibration analyzer, can you listen to the bearings with a probe or stethoscope?

 

[BrianE22]

I'd put an accelerometer on each pillow block and monitor with a scope.

 

[ivanheow]

thanks tmoose and briane22, both good ideas

when i return to england from vancouver i'll have a go with the stethoscope , the biggest problem is reaching in between the revolving wheels to try to get at the idler roller bearings , its a bit fraught !i really didnt enjoy using the infra red gun very much lol.

i really like the accerometer idea , are those sort of things readily available and cheap these days brian ?


something else i remember noticing ,is , i jumped out of the car whist doing about 100 mph ,and put my finger on the end of the strain guage,and noticed it moving in and out in a horizontal plane,

now ,this should only move in a vertical plane,so it seems to me ,maybe the whole retarder has had a knock during its life ,and gone off centre ,this would definately create an imbalance ,and maybe the noises ?

apparently they can be trued up by loosening the flange bolts a touch ,and centring it with a hammer and a dial guage .

regards
robert.

http://www.youtube.com/user/legrandphromage

 

[ivanheow]

well it turned out that the retarder was 4 thou off true ,so now its .5 thou ,after a bit of flange work .. and the bearings i have taken off so far after making a heavy duty puller ,are all pretty poor .so thats good , in a way .;-)

http://www.youtube.com/user/legrandphromage