fly wheel drill holes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mtdave2 · 11-20-2009, 01:34 PM

my trany guy says he has never seen this and thinks it may have something to do with my vibration issue. i just thought it was how they balanced the fly wheel, didn’t think much of it. i have seen lots of things balanced like this.

have you guys seen this before?

71tahoe · 11-20-2009, 02:21 PM

That doesn't look so odd to me. I do notice that the TC mount hole at the bottom doesn't look like the rest. Also, isn't the odd hole in the flywheel supposed to line up with the hole in the crank?

A new flywheel isn't that expensive and would at least eliminate that as a problem.

mtdave2 · 11-20-2009, 02:29 PM

huh? what hole on the crank?

hchad18 · 11-20-2009, 02:35 PM

Quote:

Originally Posted by mtdave2

huh? what hole on the crank?

Should be a dowel on the crank shaft bolt flange so the flywheel/flex plate lines up the same every time the same.

mtdave2 · 11-20-2009, 02:58 PM

so how can 71 see that? not sure what you are talking about. are you saying the flywheel is on wrong?

71tahoe · 11-20-2009, 03:05 PM

I think it might be turned clockwise. I can see the external crank throw through the big hole by the drill holes. The alignment hole should be in the center of that. Also there's no dark shadow behind that odd hole in the flywheel.

LONGHAIR · 11-20-2009, 03:14 PM

Quote:

Originally Posted by hchad18

Should be a dowel on the crank shaft bolt flange so the flywheel/flex plate lines up the same every time the same.

The only early Chevy cranks that have this are 400 and 454, because they are externally balanced. The harmonic balancer/dampener and the flywheel/flexplate are counter-weighted to compensate for the lack of internal weight. The others are internally balanced so the position of the flywheel/flexplate does not matter.

"In theory" a flywheel/flexplate for an internally balanced engine should have a "zero" balance, meaning that it would spin perfectly on it's own. If it is off for some reason, it could be corrected, but only to itself. It should never be part of the balance of the rest of the rotating assembly. This would make it un-useable for any other crank...but the worst part is replacing it if it should ever be damaged. The entire assembly would need to be re-balanced.

If you have a way to have that one checked w/o spending too much money, it might be worth a try.

mtdave2 · 11-20-2009, 03:15 PM

i guess it doesnt matter, they are putting a new one on.

68lwb292 · 11-20-2009, 06:46 PM

I think he was talking about the 4 holes at the 1 o'clock position that look like someone truies to balane the flywheel with a 1/2" drill bit.

hchad18 · 11-20-2009, 09:20 PM

Quote:

Originally Posted by LONGHAIR

The only early Chevy cranks that have this are 400 and 454, because they are externally balanced. The harmonic balancer/dampener and the flywheel/flexplate are counter-weighted to compensate for the lack of internal weight. The others are internally balanced so the position of the flywheel/flexplate does not matter.

"In theory" a flywheel/flexplate for an internally balanced engine should have a "zero" balance, meaning that it would spin perfectly on it's own. If it is off for some reason, it could be corrected, but only to itself. It should never be part of the balance of the rest of the rotating assembly. This would make it un-useable for any other crank...but the worst part is replacing it if it should ever be damaged. The entire assembly would need to be re-balanced.

If you have a way to have that one checked w/o spending too much money, it might be worth a try.

Good info, thanks

**WIDESIDE72** · 11-20-2009, 09:32 PM

Was the engine a 350? I cannot understand why anu drilling would be required if it is... I found out the hard way that a new flywheel ( SFI if high RPM's are expected) is cheap insurance when doing any engine or tranny work.

mtdave2 · 11-20-2009, 11:16 PM

well i looked at the fly wheel they he took out. someone did drill it, i for sure doesnt look factory. this really shocks me, for being a low mile truck, that should not have ever had the trany out.

the condition of the trany, reason i rebuilt it, and the drilling on the flywheel, make me think at sometime, someone had the trany out. hum. seems to run much smoother now, but i have not had it on the highway.

haysonj · 11-21-2009, 12:40 AM

On my 383 they balanced the crank with the flex plate and front pulley then marked everything with two lines to match up how to assemble it.

chevy_mike · 11-21-2009, 01:33 AM

Quote:

Originally Posted by mtdave2

well i looked at the fly wheel they he took out. someone did drill it, i for sure doesnt look factory. this really shocks me, for being a low mile truck, that should not have ever had the trany out.

the condition of the trany, reason i rebuilt it, and the drilling on the flywheel, make me think at sometime, someone had the trany out. hum. seems to run much smoother now, but i have not had it on the highway.

How do you know it's a low mileage truck? Do you have documentation to prove this? Without docs to prove this or knowing the truck from day one, I would never believe what the meter shows or someone told me.

**mr48chev** · 11-21-2009, 03:07 AM

Quote:

Originally Posted by hchad18

Should be a dowel on the crank shaft bolt flange so the flywheel/flex plate lines up the same every time the same.

I have about 5 small blocks around here and two big blocks plus one 250 six and one 292 six and none of them have a dowel pin.

Mtdave2 I have a half dozen Chev flex plates around here and some are drilled and some aren't.

Is there by chance a counter weight welded to the other side of the flexplate?
That would mean it was a 400 flexplate and would cause a vibration on a 350.
A good quality 350 flexplate is usually under 40 bucks at most parts houses so it might ease your mind to just go and buy a new one. Extra heavy duty ones seem to run a bit under 100 bucks ea.

t

Longhorn Man · 11-21-2009, 11:07 AM

Mike, dave's truck was a genuine 20-something thousand mile (IIRC)truck when he got it. It spent it's life in a barn. He had sent me photos and the whole story probably 8 or 9 years ago. Assembly line stickers on the drums and everything.

chevy_mike · 11-21-2009, 12:22 PM

Quote:

Originally Posted by Longhorn Man

Mike, dave's truck was a genuine 20-something thousand mile (IIRC)truck when he got it. It spent it's life in a barn. He had sent me photos and the whole story probably 8 or 9 years ago. Assembly line stickers on the drums and everything.

That's cool. Sounds like it was documented.

I just hate to hear when people buy a truck or car that the PO "claims" is xxx mileage when in fact they are leaving off the 1, 2 or 3 that should be the first number. Even worst when dealer do this crap. For me, I always assume when I see a 5 digit odo that there should be a 1 in front of it, unless I can see docs to prove otherwise.

mtdave2 · 11-21-2009, 03:24 PM

there is something odd with the trany.. perhaps the guy i bought it from did the ol trany switch-a-ro when he was going to sell it... not sure..

just one of those odd things you run into..

11-20-2009, 01:34 PM	#1
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	fly wheel drill holes my trany guy says he has never seen this and thinks it may have something to do with my vibration issue. i just thought it was how they balanced the fly wheel, didn’t think much of it. i have seen lots of things balanced like this. have you guys seen this before? __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-20-2009, 02:21 PM	#2
71tahoe Registered User Join Date: May 2006 Location: Jonesboro, AR Posts: 916	Re: fly wheel drill holes That doesn't look so odd to me. I do notice that the TC mount hole at the bottom doesn't look like the rest. Also, isn't the odd hole in the flywheel supposed to line up with the hole in the crank? A new flywheel isn't that expensive and would at least eliminate that as a problem.

11-20-2009, 02:29 PM	#3
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: fly wheel drill holes huh? what hole on the crank? __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-20-2009, 02:58 PM	#5
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: fly wheel drill holes so how can 71 see that? not sure what you are talking about. are you saying the flywheel is on wrong? __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-20-2009, 03:05 PM	#6
71tahoe Registered User Join Date: May 2006 Location: Jonesboro, AR Posts: 916	Re: fly wheel drill holes I think it might be turned clockwise. I can see the external crank throw through the big hole by the drill holes. The alignment hole should be in the center of that. Also there's no dark shadow behind that odd hole in the flywheel.

11-20-2009, 03:15 PM	#8
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: fly wheel drill holes i guess it doesnt matter, they are putting a new one on. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-20-2009, 06:46 PM	#9
68lwb292 Ex-Minitrucker Join Date: Apr 2009 Location: Bushnell, FL Posts: 301	Re: fly wheel drill holes I think he was talking about the 4 holes at the 1 o'clock position that look like someone truies to balane the flywheel with a 1/2" drill bit.

11-20-2009, 09:32 PM	#11
WIDESIDE72 Senior Member Join Date: Aug 2008 Location: Cedar Park, Texas Posts: 7,500	Re: fly wheel drill holes Was the engine a 350? I cannot understand why anu drilling would be required if it is... I found out the hard way that a new flywheel ( SFI if high RPM's are expected) is cheap insurance when doing any engine or tranny work.

11-20-2009, 11:16 PM	#12
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: fly wheel drill holes well i looked at the fly wheel they he took out. someone did drill it, i for sure doesnt look factory. this really shocks me, for being a low mile truck, that should not have ever had the trany out. the condition of the trany, reason i rebuilt it, and the drilling on the flywheel, make me think at sometime, someone had the trany out. hum. seems to run much smoother now, but i have not had it on the highway. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-21-2009, 12:40 AM	#13
haysonj Registered User Join Date: Dec 2007 Location: Santa Maria, Ca. Posts: 1,423	Re: fly wheel drill holes On my 383 they balanced the crank with the flex plate and front pulley then marked everything with two lines to match up how to assemble it. __________________ 69 Chevy 4x4 383 Power

11-21-2009, 11:07 AM	#16
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: fly wheel drill holes Mike, dave's truck was a genuine 20-something thousand mile (IIRC)truck when he got it. It spent it's life in a barn. He had sent me photos and the whole story probably 8 or 9 years ago. Assembly line stickers on the drums and everything.

11-21-2009, 03:24 PM	#18
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,521	Re: fly wheel drill holes there is something odd with the trany.. perhaps the guy i bought it from did the ol trany switch-a-ro when he was going to sell it... not sure.. just one of those odd things you run into.. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban



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