BMD serpentine pulley - bearing failure

Early Bay Forum

Help Support Early Bay Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
J

jonboylaw

Well-known member
Supporting Member
Joined
Jan 5, 2012
Messages
1,857
Reaction score
1
Location
Over the bridge in Scotland
Guys,
Yesterday one of the bearings in my BMD tensioner pulley failed, causing the wheel and surrounding to get very hot and the belt to start shredding. The bearing is actually welded itself solid and stuck on the bolt that attaches it to the carrier.
Luckily I stopped before any major damage was done (could smell something getting hot) but still had a 3 1/2 wait for recovery.

Before I take this up with BMD (less than 2000 miles on the pulley), has anyone else had similar ?

I would recommend you all go and check yours just for peace of mind.

Will replace them with some quality items from a local supplier.


Sent from my GX64 SatCom phone using Tapatalk
 
Heard loads of similar stories, I was going to have one on my Engine but Laurie Pettitt advised me of the BMD horror stories and we fitted the MST version instead. Just to warn you as well I think LP may have also mentioned the BMD is no more :(
 
I just took the idler wheel apart.
The bearings are 6201z's a standard size, but have no manufacture marks and look to be of poor quality. I'll replace with quality items. I have written to BMD.
Yeah, Laurie recommended getting the MST crank bolt and alternator nut which I did.
Shame such crap is released in the market, could have easily snapped the belt and fried my engine




Sent from my GX64 SatCom phone using Tapatalk
 
I suggested this kit for my 2110 but my mate who's building instantly said no! Went for a tried & tested combo: Gene Berg equaliser & a Bugpack spin-tru ;)
 
I think Karlos is right, I know they look cool but that's about it.
Last year on the way to Ninove we stopped to help 3 busses that had all broken down with brand new £10k motors running these serpentine kits.
 
jonboylaw said:
I just took the idler wheel apart.
The bearings are 6201z's a standard size, but have no manufacture marks and look to be of poor quality. I'll replace with quality items. I have written to BMD.
Yeah, Laurie recommended getting the MST crank bolt and alternator nut which I did.
Shame such crap is released in the market, could have easily snapped the belt and fried my engine




Sent from my GX64 SatCom phone using Tapatalk
Click to expand...

I'd be interested where you get the replacement bearings as I'm running a BMD, and was concerned about the bearings, if you could let know when you source some that'll be great.
 
Just type in 6201z bearings in google and find a local supplier. Go for a quality bearing makes from a reputable supplier ( go to a local shop) so you know they are genuine.

The bearings themselves are 12x32x10 mm.


Sent from my GX64 SatCom phone using Tapatalk
 
Buy the best branded bearing you can get.

SKF, FAG or NSK are pretty reliable, also look at the seals on it.

6201 is the bearing size reference. The letters after the numbers tell you something about the sealing properties:

Z is a metal cover/shield
RS is a rubber seal (can be removed to pack extra grease)

So 6201Z has 1 side with a shield, I would have thought that covers on both sides would be better (6201 ZZ) or even rubber seals (6201 2RS) as you can pick out the seal & add extra grease. There are other seal options, but these are the most common type.


Sent from my iPad using Tapatalk HD
 
bmd nolonger trading eh! well at least that should cutdown on bearing failures, but thats not the only problem I have seen with these pulleys - top to bottom pulley allignment is also suspect in some cases so excessive side loadings on bearings and premiture belt wear are only the start of the problems. I would stick with the factory set up unless I were screwing stupid hp thru the motor.
 
junkyard_dog said:
bmd nolonger trading eh! well at least that should cutdown on bearing failures, but thats not the only problem I have seen with these pulleys - top to bottom pulley allignment is also suspect in some cases so excessive side loadings on bearings and premiture belt wear are only the start of the problems. I would stick with the factory set up unless I were screwing stupid hp thru the motor.
Click to expand...

It's not HP that matters, its rpm. The amount of HP used by the fan, which has to be transmitted by the fan belt, rises exponentially or by the square of the rpm. Eg. If the fan uses 5 bhp at 3000 rpm it does not use 10 at 6000 but much more.

On a high revving engine the stock system will start slipping when the load gets too high but with a serpentine there is a good chance it won't. If the fan is over revved there is a chance of damage, hence why the racers use strengthened welded ones. They also use a heavy duty belt with is appropriate pulleys since the stock type belt will be over loaded at high rpm.

Another motor sport solution is to change the gearing by fitting a smaller lower pulley and/or a larger top one but this is no good for normal road use since the fan will provide too little air flow at lower rpm.

I have heard of a few of these serpentine kits suffering bearing failure but I am not sure if its due to under specked bearings or due to incorrect alignment causing excessive side loads.

On a normal road going vehicle I honestly can't see the point of these since your not going to run the kind of rpms that need extra belt traction. The premis of easier belt tension adjustment doesn't hold good either really, since I have only ever needed to adjust the belt tension once after fitting and that was because the belt should really have been replaced, since it was significantly worn and hence narrower than it should be. A reasonable quality belt does not stretch, it wears away and hence sits lower in the V of the pulley.
 
jonboylaw said:
I have now sourced the bearings and axle bolt. If anyone would like to change their's please let me know as I have a spare set of bearings and a shoulder bolt.

It looks like BMD are no longer trading.
Click to expand...

How long did your bearings last Jon??
 
Sorry, I did not see these follow ups. My bearings lasted about 2k miles. I am keeping my eyes on the tensioner each time I take it out now. Did do a 300 mile run a couple of weeks back and all was ok. You don't need to put too much tension on the belt as they are ribbed and do not slip easily.


Sent from my GX64 SatCom phone using Tapatalk
 
Ive got one on my 10K motor, haven't fitted the motor yet but i do plan to horse the shit out of it.

[youtube]9-DERgR4rXQ[/youtube]

Just ordered 2 FAGs on ebay. one for the spares bag, you never know.
 

Similar threads

ZedBed
For sale : improved BMD serpentine pulley kit - SOLD
Replies
0
Views
391
ZedBed
ZedBed
B
How To: Prep and Re-Spray
Replies
3
Views
1K
privatejobs
P
Tezzah
  • Locked
SOLD - 72 Crossover with westy roof
2
Replies
23
Views
3K
Tezzah
Tezzah
poptop2
Rhubarb resto the story so far
2
Replies
27
Views
4K
poptop2
poptop2

Latest posts

Top