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Mercury 800 SC's has no boost,Why?

Old 06-25-2013, 01:25 PM
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Rob
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Question Mercury 800 SC's has no boost,Why?

I have a buddy that has 1999 merc 800's sc that have about 180 hours since a sterling rebuild, One motor do not have any boost and does have good steady vacuum,it did it once before and this time it stayed, He said it seems like once its run and get warm it happened,its also down 500 rpm, What could cause this set up to not have any boost? The weind/b&M supercharger were rebuilt about 10-15 hours ago.and about 2 years ago.Said it had a little slack in the snout gears,He said its not popping ,seems to be running fine except for the rpm and boost.The boat has been sitting,He hasent looked at it since it did this last weekend,Trying to get some ideas before we jump into it.

I thought about a valve sticking?

Guessing if Intake rocker broke would make more boost.stuck open back firing up the intake.

Exhaust sticking or not opening?

Intake leaking when in boost?

Blower coupler broke in front.



He was thinking the belt is slipping when it trying to go into boost.,ribbed belt.

If the belt is worn and the pulleys worn and shinny would it still put black belt dust?

Thanks


Rob
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Old 06-25-2013, 04:41 PM
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Originally Posted by Strip Poker 388
I have a buddy that has 1999 merc 800's sc that have about 180 hours since a sterling rebuild, One motor do not have any boost and does have good steady vacuum,it did it once before and this time it stayed, He said it seems like once its run and get warm it happened,its also down 500 rpm, What could cause this set up to not have any boost? The weind/b&M supercharger were rebuilt about 10-15 hours ago.and about 2 years ago.Said it had a little slack in the snout gears,He said its not popping ,seems to be running fine except for the rpm and boost.The boat has been sitting,He hasent looked at it since it did this last weekend,Trying to get some ideas before we jump into it.

I thought about a valve sticking?

Guessing if Intake rocker broke would make more boost.stuck open back firing up the intake.

Exhaust sticking or not opening?

Intake leaking when in boost?

Blower coupler broke in front.



He was thinking the belt is slipping when it trying to go into boost.,ribbed belt.

If the belt is worn and the pulleys worn and shinny would it still put black belt dust?

Thanks


Rob
sounds like the teflon strips are wore out..?? maybe,,tell him to take the blower belt off and to see if he feels any restriction when the blades come in contact..if it just free wheels when he spins it then the strips are wore out..
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Old 06-25-2013, 06:51 PM
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Strip does he have the stock 10 rib setup still? Those setups were overdriven a bit, and don't take much for it to slip the belt. I'd look into replacing the belt and tensioner. DONT buy the tensioner thru merc. Its a GM part that's 50 bucks. Merc wants several hundo. Just need to transfer the pulley onto it. I'll get you the part number for a new tensioner from GM if you need it.
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Old 06-25-2013, 10:46 PM
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Originally Posted by MILD THUNDER
Strip does he have the stock 10 rib setup still? Those setups were overdriven a bit, and don't take much for it to slip the belt. I'd look into replacing the belt and tensioner. DONT buy the tensioner thru merc. Its a GM part that's 50 bucks. Merc wants several hundo. Just need to transfer the pulley onto it. I'll get you the part number for a new tensioner from GM if you need it.

Every thing is stock,it only had 10-15 hours since The Blower Shop rebuilt it,Strips? We've been talking and hopeing its just a belt,Its old,,If ya get a chance on the part # I would appreciate it just incase. I will be going down there for the fouth of July help him figure it out,Im hopeing we can figure it out before so we can have what ever parts we need to fix it.

Also this problem started out as a intermitet and the last time he ran it after running for a while it started and didnt stop the no boost.kinda thinking/hopeing its the belt being it

Hey you guys let me know what you all think, Give us some ideas.Yawlls help would be appreciated

Rob
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Old 06-25-2013, 11:10 PM
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I'd replace the belts with either the Gates Fleetrunner heavy duty or Goodyear Gatorbacks. Need the old part numbers off the belt for cross reference. They are usually 25-50 bucks a belt.

Back in the day it was very common for guys with the 800SC's to upgrade to the 16 Rib PFM marine setup. Stock they are pulley'd 18% overdriven, which is a lot for a big old roots blower with a 10 rib serpentine. But, I think with fresh tensioners and belts you should be good. Even if the Teflon was worn, it'd be making a little boost. Not 0. If the engines running fine around the docks and low speed, and nothing erratic goin on the vacuum gauge, i'd keep it simple . The coupler is splined, so its either turning the blower or it isn't, no chance the coupler is slipping so to speak.
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Old 06-26-2013, 12:57 AM
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On my 525SC, after about 50-75 hrs, the boost would drop 3-4 lbs all of a sudden.
A new belt would solve the problem. I always kept a spare on board. They were 10 rib belts also.
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Old 06-26-2013, 01:29 PM
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]I'm hoping the belt is it,He already has new ones that came with the boat,Ill get him to do this first,ill be down there next thru if that doesn't fix it,any other suggestions?

I guess at 18% that's spinning the shet out of it, pretty good load on the belt,

I know on my Whipples the 10 rib belt in the beginning would slip and create black dust on the front plate,after recoging the tensioner it never does it any more,But when it took a dump it rolled the belt off 2 teeth,Ive been running the Napa belt since 2005,I guess its time for me to replace mine also.

I really appreciate the help!!

Rob.

Thanks guys for all the help!!!

Rob

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Old 06-27-2013, 11:09 AM
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Well I talked to him last night, he said the pulley free wheels,so the coupler broke,he ordered a new one 350.00 from the The Blower shop. previously they didn't have a replacement when they rebuilt the the first time, at-least they have a fix.

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Old 06-27-2013, 11:14 AM
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Originally Posted by Strip Poker 388
Well I talked to him last night, he said the pulley free wheels,so the coupler broke,he ordered a new one 350.00 from the The Blower shop. previously they didn't have a replacement when they rebuilt the the first time, at-least they have a fix.

Thanks
Rob
Yup, that'll do it! Pretty cool that the blower shop has stuff for those blowers. Couplers, snouts, billet front covers, etc. When I rebuild mine i'd like to upgrade to the blower shop pieces.

Anyhow, glad you found the issue.
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Old 06-27-2013, 12:52 PM
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Originally Posted by MILD THUNDER
Yup, that'll do it! Pretty cool that the blower shop has stuff for those blowers. Couplers, snouts, billet front covers, etc. When I rebuild mine i'd like to upgrade to the blower shop pieces.

Anyhow, glad you found the issue.

Yea they seem to have alot of stuff,I have the old littlefield off my Scarab and Im trying to put it on my Chevelle,but it has a full rear set back,have to change up a bunch of stuff ,Ive been weighing selling it and buying the Blower shop 8/71 made for a small block,im figuring about 2-$2500 I could get the blowershop one.

Would be nice if one of my old Whipples was a top feed,I would be putting it on the chevelle


im going to take some picture of it when we get the blower tore down,should be cool
Rob
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