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[Stu Jackson]

Ken, that worked for me for years on our old OEM alternator.  That's because we then used a 7390 belt.  When I installed our new alternator a few years ago, we moved up to a slightly longer 7400 belt.  That made the adjustment bolt on the engine almost bottom out to the slot in the bracket.  I couldn't do the "through the door" trick anymore and we bought the belt tensioner tool.  The length of the belt may have an impact on whether or not the old trick will still work.

[Ron Hill]

For those that have the M35B/M25XPB with the adjusting bracket on the top, you may not need this tool. 
Seems that pressing on the alternator + its own weight allows you to easily tighten. 
Unsaid - is that you have to loosen the top and bottom nut so the alternator will move.

[Tom Clay]

True Ron,

Seems that pressing on the alternator + its own weight allows you to easily tighten.  

If you have the M35B loosen top bracket and just push on the alternator till belt is tight. 

[sail4dale]

To much tension caused a failure of my salt water pump on the M25 engine in my old Cat30.
        I thought I was being a great mechanic when I really leaned on the alternator and tightened down the holding bolts.  Yeah ... real good   it side-loaded the shaft on the water pump which froze up.  Shortly, the belt which wanted to keep turning proceeded to fry and smoke big time. 

Limped back to the dock and replaced the water pump.

Hey, a loose belt is not that bad IF it doesn't slip.

[Stu Jackson]

One of the reasons we keep asking you to advise us on what hull # and engine type you have is exactly this.  

Each engine has different characteristics and details, like alternator mounts and tightening.  Push UP on one, and DOWN on another.  

Please help us to help you by providing as much information as you can.  

You can use your signature to do so, as we have including our engine model #.

[Hawk]

Good news on the M35B. One less tool. Looking at it I thought in a pinch I could just lean on the alternator to tighten. Nice to hear its official.

Hawk

[Steve Sayian]

M35's:  Make sure you loosen the bolt on the bottom of the alternator bracket before you try moving the alternator.  It's underneathe the alternator and hidden by wiring harnesses.  Kind of difficult to get access to.
I just replaced my alternator last weekend and had quite a time getting in there.

Steve

[Stu Jackson]

For photos of an M35, go to Reply #12 ++++ at: http://c34.org/bbs/index.php/topic,4588.0.html

[Braxton]

Ron did you buy the tool that you sent the link out to?   Is it indeed the right item?

[Stu Jackson]

Dale, re: your "loose belt" note:  too tight = NOT good (fresh water pump), too loose = ALSO not good (alternator)!  That's why one needs to do it correctly:  1/2 inch deflection, 90 degree twist on the long length from the pump to the bottom of the alternator.

In this thread: http://c34.org/bbs/index.php/topic,4454.msg27184.html#msg27184

John Nixon included this very important piece of advice in Reply #21, which bears continued repeating (just in case I haven't done it a few times before already! :

Most alternators that die from over-heating will do so from a slipping belt. At higher rotational speeds and high loads, the slipping belt will heat the pulley and rotor shaft to many hundreds of degrees. These elevated temperatures will cause the front bearings to fail first, which then causes the whole front case and rotor of the alternator to get even hotter. I have seen an alternator rotor that got so hot in this situation that the solder melted out of the slip ring terminations of the field winding. Needless to say, this sequence quickly becomes a catastrophic failure of the alternator.

While increasing air flow to the alternator is never a bad thing, the real killer is improper belt tension. If you are running a single 3/8 inch belt and a high output alternator, you need to watch your belt tension like a hawk. The nifty belt tensioner tool in a previous article will become your alternator's best friend, and make tensioning your belt easy enough that you will be without excuse.

[Ron Volk]

Braxton,

I did not buy one yet, info on it says it extends to 15" and it looks like the picture posted earlier.  Maybe a call or email to their customer service dept. would confirm it.  Since I have not actually seen one other than the picture, maybe somebody on this site that has one could confirm that this item would work.

Ron
GOOSE III #1235
Dana Point CA

[Craig Illman]

Braxton - The one shown on the MSC site looks like the one I bought from JC Whitney.

Craig

[Braxton]

Ok, we'll now have at least two of them in fleet 5.    If anyone else in the south Sound needs the tool just bug me and I'll get it to you.

[Stu Jackson]

I found one at www1.mscdirect.com part #35438209 (Belt tension jack). this looks like the same type.

Anybody tried this in addition to Ron?  Anything new in terms of sources?

[Ron Hill]

Guys : If anyone with a M25 engine (with the adjusting bracket underneath) that needs a belt tensioning tool there are a number of sources for about $10 :
NAPA
Harbor Freight
J.C.Whitney

As I previously mentioned, if your adjusting bracket is on the top of the alternator like the M25XPB & M35BC, you don't need this tool to properly tension the drive belt.  A thought