BDS setup, Belt Tension..?

[George1301]

Hey guys... kinda new to this...
Have a 468BBC with a 8-71 BDS setup...
When I fired it on the trailer for the first time since the renovation... egine started, and ran GREAT...!
One thing I noticed...
As the egine is raised off idle to about 2,500-3,000 bursts....
The belt tends to "walk" towards the end of the pulley ( not off though )...
As the engine comes back to an idle... the belt returns to center position...
Movement is only about 1/4"... Seems the idler pulley flang is maintaining it..?
Have the longest 8mm belt on this...
Pressing with my thumb, ( very scientific) I get about 3/8" deflection.

Thoughts..?

I am putting this ride in the water this weekend for the first time...

GS1301

[tunnelrunner]

The belt tends to "walk" towards the end of the pulley ( not off though )...
As the engine comes back to an idle... the belt returns to center position...
Movement is only about 1/4"... Seems the idler pulley flang is maintaining it..?
Have the longest 8mm belt on this...
Pressing with my thumb, ( very scientific) I get about 3/8" deflection.

Some of the other guys might want to chime in on this one, but here is my 2c worth..:D

Its not unusual to get some "walk" in your blower belt, but it is most definitely worth checking your pulley alignment, especially if you have just done a rebuild. Your belt deflection is within limits, but get someone to blip the throttle for you and carefully watch the belt as it walks onto the idler pulley flange. If it "looks" like its trying to "climb" it, you have a problem.... and trust me, 8/71s aren't real efficient tunnelrams...which is what it will try to be when you throw the belt.;)

Have you had the engine apart or replaced any components in the blower drive?

[wagspe208]

3/8 is to tight unless the engine is totally hot in my opinion.
Is it the Kevlar belt, or rubber?
Walk is very common on the surge.
8mm belts have lenty of tooth contact area. You are not tightening the belt like a v-belt. I probably run mine a little loose. (drag application, kevlar belt)
Honestly, it wouldn't surprise me if mine was 1" or a little more cold. I am sure it is at lleast 1/2 " hot. Probably more like 3/4. The kevlar is not forgiving. The rubber belt may be.
Wags

[Flatmvn]

Pressing with my thumb, ( very scientific) I get about 3/8" deflection.

I would not worry about the walking back an forth it will do it a small amount.
If you are referring to the belt tension as deflection then your belt might be to tight. Tension should be adjusted to 3/4 of an inch cold and 1/4 of an inch hot ( normal operating temp ).

You have to remember that as your engine heat builds the engine and parts expand. This will make the belt tension vary. That is why there is such a large tension spread.

Louis

[gfinishline]

Put a straight edge on the top pulley, down to the others. Are any of them out of alignment? (idler is wider) Do this with all (top, idler, and crank) see if you have an alignment problem, or just a too tight of belt. The belt will move around because of the LOAD, but it should not "skip", or "bounce' at any time. Tiny pieces of belt will fly all over, (like paint overspray) but no pulley should have black marks on it. Iron block with iron heads about 1" (off center) of play at long side. Aluminum heads about 1/4" more, all aluminum 1 1/2" to 2" as to deck height. This is why everyone got away from "1/2" pitch square tooth belts". They would actually "roll over" the teeth at high speeds with this kind of slack. If you park the boat for more than one week, REMOVE the belt and let it rest unshapen, on it's edge, in a cool place. If you have a 1/2" pitch square belt drive, use large diameter pulleys.

[raysoninoz]

I'm just jumping in to add weight to what the other guys have said.The fact that it certainly seems like the belt is TOO tight. Don't worry about the 1/4'' walk. Like wags has said, 8mm belts have plenty of contact area & gfinishline has it all answered for you.
Cheers. Hope you enjoy your boating weekend. It's getting a bit cold down here (in Oz) to be playing in the water.

[George1301]

I have the Mark IV block... Eldo aluminum heads... 8-71 BDS with the 8mm belt setup...
Sounds as though I should be OK... maybe a bit on the tight side... will re-adjust before firing again.
You guys are great..!
Thanks,

GS1301

[RiverRacer]

If you think the belt is loose when it's cold, just make a good hard pass then check it, you'll be surprised at how much stuff expands when it gets hot!...

[Terrible toy]

All the blown race motors I've had experience with had supports on the crank pulley. Anybody know what the hp, rpm, boost, blower speed breakover point is where that becomes necessary?

[hydroguy]

I don't have a blown motor (yet) but I have researched them. I would say somewhere between 700/1000hp and over 18lbs of boost, after that point the strain on the front crank pully starts to get more severe (is that redundant). I know that N/A motors can make more HP than that but they dont have the strain of a blower on the crank. Your milage may differ.

[Terrible toy]

Ralph Gorr, who did the flow work on the Buzzard Catcher injector on my Alky dragster, said that on a 2500 hp motor a 1471 high helix used upwards of 300 hp to turn it. I guess that would put some strain on the poor ol crank snout.

I understand the top fuel guys are around 1500 hp in parasitic loss in their engines.:eek:

[wagspe208]

I figure wth my old Kurtis took 900 to 950 hp to run the 8.0 class. Probably another 250 to 350 to run the 1000' 6.0 class. My boat had a small diameter prop and left "slow". Term it what you like. I had a Kevlar belt. No front suport. I cannot tell you boost level. It is a 10-71. Hardest I ever drove it was +20%. (missed the tuneup by quite a bit LOL) Usually it was the -10% to -2% range. I went throuth the lights at 8000 rpm. I broke several sprags in the beginning, a prop shaft once, I think thats it. I had a 9500 rev limiter in the MSD. Never a belt issue. Same belt since 99, in fact. Literally hundreds of passes. 8mm BTW OH, front brearing never showed any signs of abuse. Top or bottom.
Now, that does not answer your question directly. Just my experience.
Some of the boat guys I did work for built blown pump gas pieces. Pleasure stuff, so really endurance. No crank supports even with thir 1200+ hp stuff.
So..is a crank support necessary? I guess it may add insurance. Do not overtighten your belt. I think the popularity filtered down from the real BA dragster classes and now it is just considered necessary.
They do look cool. They are not cheap. They make it a PITA to change that lower pulley.
Pros vs cons is up to you.
Wags
Back to barn to work on that white bitch.

[Terrible toy]

Well there in lies one of the problems with a lot of race parts, that is when do you really need it. You're right the supports are expensive and they do add to the labor if you change pulleys, especially at a race when you're pressed for time. But, guys that had a lot more experience then me said I needed one so I bought the thing.:rolleyes:

[George1301]

OK guys... I am new to this... What the He.. does this support look like...? :)
Not that I am going to rush out to get... ( Don't like "bellie-Button" setups )...
The most I ran was a Jackson setup on a 409 in a 63'... was fun on the street... :)
Had to take stock out in pushrods though... I know it was not a boat, but the script on the sides for body art was, " Midnight Special... Alias the Boat "... Was a Impala... Tube frame, Dana 60 w/5:13's... Lenco... and of course the mighty 409...Ran hi 9's but was somewhat a handleful to launch... had a straight axle in front... kinda a squirrel.
I have worked on these boats for years over at Bill Morris's Shop in Whittier in the 80's.
I always wanted one... now I have it... :)
Anywho... I will step down...
Plan to hit the H20 Sunday...

GS

[Flatmvn]

It looks like this

http://www.sporttruckdirect.com/Pics/ASP/ASP_Crank_Pulley_TB_front.jpg

[Flatmvn]

Oh sorry wrong style of crank support I this is the one that you are actualy looking for.


http://www.kenlowe.com.au/_borders/KLRC_F101.jpg

[RiverRacer]

I've often wondered about the limits on the crank snout, K boats have been known to run 1400hp plus drive off the snout as well and still not fail!..

[George1301]

Ok... I can make these in a mill...
Anywho... Set the boat in the water for the first time out...
I had water coming in alot at the trim handle... seems when I installed the rod back to the trim plate area... I forgot to plug the tubing as it came all the way down into the boat... Back on the trailer to fix...
Put it back in the water... fired up ... got about 1/4 mile... tensioner pulley locked... burned my new belt... seems the outside bearing came apart & seized...
Back on the trailer... barrowed a freind's... Back in the water...
About 1/8 mark... the shat going to the Casale began to vibrate... scarry... came back onto the trailer again... Done
We all went back to the house had a pool party & suds...
Weekend will pull the shaft out and see what I did wrong..?

GS

[RiverRacer]

Hmmmm, that brings back memories!..:D

[George1301]

After this last weekend... Set it in the water... fired and off to have some fun...no such luck... The idler pulley bearings seized one of the bearings.... locked up and smoked the 8mm belt...
After three different attempts to launch again... gave up and trailered back to the house. We spent the rest of the day with our friends... pool.... beer... and more beer.
One of the main reasons I decided to give up... Seems a lot of vibration on the shafting to the Casale... enough that it knocked the tube loose...Will chk this weekend...
Anywho....

GS

[shooter2]

Hmmmm, that brings back memories!..:D

One year we timed the age of the motor by how many tanks of gas we put through it. So not to worry all of us here have done our fair share of follies. Keep us posted as it is good to know that there are others out there like us.

Brian

[RiverRacer]

Seems a lot of vibration on the shafting to the Casale... enough that it knocked the tube loose...Will chk this weekend...
Anywho....

GS

If you have u-joint driveline you might want to check that out also!..

[George1301]

Have a driveline issue as well I think... Lots of vibration when I drop in gear at given RPM's...?
The Belt... 8mm... now scrap.
I also posted in the classified arena... Looking for the mounting ring that is mounted on the input shaft end of the Casale... Seems the shop that did the first work on the trans lost it... I thought I could just "pinch" it with a few bolts threaded about the bearing housing... NOT...
Anywho... If anyone out there has a "spare" housing..?
The idler pulley arrangement... BDS... 8mm.... Missing the spacer between the bearings...? Looking for that as well... I could machine up I guess...
Frustrated, but will not give up on this... :)

GS1301

[Flatmvn]

I might have the spacer for the belt pully I broke a pully but the bearings and spacer are still good. I will have to see if I can find it.

Louis

[George1301]

Thanks... Will check back later....
I took everything apart tonight...
The bearing, # 5205 seems OK, but now do not trust.
As for the rest of parts...

GS

[RiverRacer]

Lots of vibration when I drop in gear

How's the u-joints??, what about the strut bushings??, you check to see if the prop shaft is bent?, what shape is the prop in??, all can contribute to vibration!...

[George1301]

Strut bushing seems OK... The prop I just replaced... steel unit... Looked good, but have not maged it or anything... Funny... as I was laying under this and pondering how at the time I would ever locate a set of hull fins... I noticed a crack in the prop right at the keyway on the nut mtg. side of the prop... Decided right away to replace.
Take a look at your PM's...

GS

[RiverRacer]

Strut bushing seems OK...
Seems ok???, how much slop is there???..

Take a look at your PM's...

Back at ya!..;)