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View Full Version : Engine Belt Tensioner on LT-1 Corvette Engine


Jonathan
06-28-2010, 01:48 PM
Hi Guys

This is my first Thread to TT. I'm in Ireland and so I need some help from you guys State Side. I purchased my first boat (a 1999 Maristar 200VRS with LT-1 Corvette 350hp engine in it last July) Love the boat as do all the family. Since getting the boat I have followed alot of your Threads and needless to say its a great source of information.

Was out in the boat 2 days ago when I noticed fluff and bits of rubber in the engine compartment. I figured out it was the Engine Belt for the water pump and alternator. The Belt is totally gone but the guy who sold me the boat happened to have a spare one for that boat when he sold it to me. It is the correct belt for the LT-1 engine.

Anyway I got the belt onto the crankshaft drive pulley and the alternator pulley but I was having difficulty getting the belt over the belt tensioner. I downloaded the 1999 Maristar manual from the MC website but it only gives information about the Vortec MX Plus engine (which has the adjustable alternator mounting - the LT-1 does not have the adjustable alternator mounting). The manual goes on to say that on engines with serpentine belt systems, no change in necessary - belt tension is maintained by the automatic belt tensioner. The relvent page from the Manual (1999 Mastercraft Owners Manual Page 49 in the PDF document in the My Mastercraft section of hte MC site) I confirm that end of my engine looks like the diagram. I could not upload the relevant page for you - sorry!

I did loosen the nuts around the belt tensioner wheel and it would only move up the way (this did not help as I need the wheel to move down the way to get the belt over it) I then open up the nut in the center of the belt tensioner wheel and lifted off the wheel. underneath the wheel I found a nut in the center which can be loosened with an allen key (don't know if you call them the same thing its a screw with needs a hexagonal key inserted into it to unscrew it). I unscrewed it and this made the entire unit come slightly out of it's housing but it also dropped down the belt tensioner unit enough for me to pull the belt over the unit with the wheel back on it. It would not let me tighten the hexagonal screw inside the tensioner unit back to it's original position (when I did it just moved the unit back up and made it too tight to get the wheel back on with the belt over it.) I thought maybe the unit (to include the hexagonal screw) would automatically tighten up the unit and tighten it back into the housing and also push the belt tensioner wheel up higher to tighten up the belt itself. I fired up the engine and let it run for 10 minutes but it did not tighten up the unit behind the wheel or the belt itself. I know there must be some sort of a trick to this problem and I hope you can help.

The belt should be tight enough so it will deflect 1/4"-1/2" when pressed with the thumb. Mine deflects about 4"-6" When I start the engine the belt is working and the alternator is turning over but I understand if it is too loose the alternator will not get a proper charge and it will lead to the belt wearing out too quickly. Also the Belt tensioner wheel does not spin around as the belt runs over it (I'm not sure if it is meant to spin or not and maybe you guys will know the answer)

So couple of question for you
1. Does the Belt Tensioner wheel usually spin around when the engine is running with engine belt running over it?
2. Is there some trick to getting the belt onto the LT-1 (as it does not have the adjustable alternator)?
3. Should I have to open up the belt tensioner and going adjusting the hexagonal screw inside it?
4. It I do need to adjust that Hex screw how do I get it to tighten up and let me still get the wheel back on it and the belt over it?

Sorry this is so long but I thought I better give you as much information to help rule things out.

Help please!

91prostar
06-28-2010, 02:43 PM
Hey there can you post a pic? Most gm belt tensioners are moved by inserting a 1/2 inch pull bar or rachet into it to and pulling release the tension. This would be for removing and installing a serp type belt. A pic would confirm this, I hope I understand the problem correctly..

Jorski
06-28-2010, 06:02 PM
I have a 1993 LT-1...your set-up maybe different.

I have always loosened the bolt that holds the alternator in place. Once loosened, it slides towards the center of the engine.

To increase and set the tension: there is a hole in the top of the alternator bracket. I put a lrge flat head scredriver through the hole and I can push against the alt. to pry it as tight as i want the belt to be. While maintaining pressure on the screwdriver, tighten the bolt and you should be good to go.

blackcreek
06-28-2010, 06:56 PM
You put a wrench on the tensioner pulley bolt(the one that holds the wheel on) and turn it clockwise like you are trying to tighten the bolt more. The tensioner wheel arm will then move down so you can slide the belt on then you release the tension by releasing pressure on the wrench. If you took the tensioner itself apart you may have released the preset spring load, don't know how you are going to fix that.

Jonathan
06-29-2010, 05:51 AM
thanks for coming back so quick guys. I think Blackcreek might be on the right track. The good news is I have not taken the tensioner apart. I only loosen the screw in the middle of it and stop from going all the way as I figured there was a spring inside it. I will tighten up the tensioner unit and try to tigthen the bolt on the wheel as suggested and see what happens.

If all goes well and I do get the belt on over the tensioner wheel - is the belt tensioner wheel meant to spin around when the engine is running and belt is going around the alternator & crankshaft drive pulley?

Thanks again

vogelm1
06-29-2010, 08:44 AM
thanks for coming back so quick guys. I think Blackcreek might be on the right track. The good news is I have not taken the tensioner apart. I only loosen the screw in the middle of it and stop from going all the way as I figured there was a spring inside it. I will tighten up the tensioner unit and try to tigthen the bolt on the wheel as suggested and see what happens.

If all goes well and I do get the belt on over the tensioner wheel - is the belt tensioner wheel meant to spin around when the engine is running and belt is going around the alternator & crankshaft drive pulley?

Thanks again

The tensioner wheel should spin free...that may be why you blew the belt. If the bearing in the tensioner is frozen up all the friction from the belt sliding across the stationary wheel will fry the belt. You may need a new tensioner wheel then too. There's a chance you can press the old bearing out of the wheel, but it may be easier to take just the wheel off (not the whole tensioner) and get a new one at the auto parts store.

Jonathan
06-29-2010, 10:32 AM
Ten out of ten for Blackcreek. I went home at lunch time and did as he suggested and sure enough the belt tensioner moved down enough for the belt to slip over it. Job done in 5 minutes and the belt feels nice and tight. Blackcreek thanks a million and to all the rest of you for you help. Thanks for you advice too Vogelm1 when I get it back on the water I will know if the wheel is spinning - I think it is ok but I know what to do if it's not. Cheers again