Flex Plate

Sir, Have you tried rotating the flexplate? IIRC it will only fit in one position as 1 hole is a little off. I do have a used one if you can't find
one closer than Tennessee.

> GMC'Ers
> so I have ordered tWO flexplates so far ATP Z116 AND PIONEER FRA 102, I also tried a buick just because and nothing is matching up to the bolt
> patterns on the crank. Does anyone have an idea where to get one? Is there a used one out there? its quite difficult to break in an engine if you
> cant start it?
>
> thanks
> Grant

--
C. Boyd
76 Crestmont
East Tennessee
 
Sir, just a note.. the welded on weight on the flywheel goes toward the torque converter. If one hole is off, rotate to next hole and so on till all
6 line up. It will only go 1 way as the engine is externally balanced. I am surprised the engine builder did not include the flexplate as it is
needed to balance the engine, unless he did not balance lt?

> Mr. Boyd,
> Thanks. I have one more heading to me in the mail. I will let you know, thansk

--
C. Boyd
76 Crestmont
East Tennessee
 
> Yes that was the frustrating part, I rotated to where all lined up except 1. 5 out of 6 is not a bad thing but i really dont want to alter the
> holes on the plate. maybe I have bad holes on the plate?

Grant,

Did you try turning the plate over? Maybe you are trying it the wrong way.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Sir, I can't tell anything from your pics. Back up a little so the whole flexplate can be seen. Mark 1 hole with paint spot and take 6 pictures of
the flexplate in the 6 possible combinations with the weight showing.
Where did the engine come from? Was it a running engine or assembled from floor parts?
Do you have the flexplate that came with engine?
Have you checked with the engine builder? If he is clueless you better check to see if it has the correct oil galley plugs with holes to spray oil on
timing chain and distributor gear.
What heads are on engine? Are rocker attachment bolts 5/16 or 3/8?
Here are some specs.. https://oldsjunction.classicoldsmobile.com/oldsfaq/ofblk.htm%201965%20-%201976%20Identifying%20a%20Big%20Block%20Block
Table of contents at bottom of page.

Early 68 is when Olds changed flexplate mounting holes but I have never heard of a true 455 with early bolt pattern. Was the engine originally red?
Did it have a 2 bbl or 4 bbl carb?
All flexplate pre 68 have 1 mounting hole offset 5* ccw and 68 and later 1 hole is offset 5* cw.

You may have to remove oil pan and work off the crank numbers.
https://oldsjunction.classicoldsmobile.com/oldsfaq/ofcrk.htm

> Mr. Boyd,
> Yes the weight goes out towards the torque converter. on a post recently i added some pictures so everyone can see. it is awfully frustrating as I
> cant dyno my engine and get it installed with out a flex plate.
> any ideas?
>
> Thanks
> Grant

--
C. Boyd
76 Crestmont
East Tennessee
 
Sir, the 68 cast in the rear of the block is the Julian date (1-365) of the year the block was cast. Since yours is Fa it is 72-76 nothing strange
there. It looks like if you were to rotate the flywheel about 5* ccw on the crank then 5 bolts would line up and one would be off center 5* cw which
it should be and you should have the correct flywheel according to the #'s.. I still think you just need to rotate the flywheel on the crank till all
6 bolt holes line up. Just keep turning it to a new hole and somewhere all 6 will line up. Make sure the welded weight is facing outside toward /
against the torque converter.
On the date built it is on some cars stamped with VIN number on oil fill spout then painted over. I have not found any on motorhome build engines as
the oil fill tube end is motorhome only. Has a fill hose instead of spin on fill cap. If you do find a number the first # is the year, should be
2-6.

> Not sure on any of these as my engine builder is supposed to be a BOAT guy. I picked up the engine from a local GMC'er and quickly took it to get
> built. So relaying on my builder probably is not a good idea. there was not and origianal flex plate so this is where I am at. I suppose it is time
> to remove the engine pan again and do some research.
>
> 396021 fa is the casting number next to the oil filler tube, according to the "oldsmobile FAQ site The block is "common" but the back casting is a
> 1968 not a 72 on, obviously there is something wrong.
>
> ID/ Casting
> Code Year(s) CID Number Notes
> A '65 425 381917?? 1st year, big cars.
> 386525
> B '65 400 389298 442 only, one year only.
> D '66 - '67 425 389244 Big-car engine. Toro is different internally.
> E '66 - '67 400 390925 442 engine [VERY rare].
> F '68 - '70 455 396021 Common big block. Stick type F (sans serif).
> F '70 - '72 455 396021 Common big block. Serif type F. Two vertical
> and a base serif.
> Fa '72 - '76 455 396021 Very common big block. Marine also (L VIN derivative).
> G '68 - '69 400 396026 442/Vista/etc. engine.
> L '76 455 231788 Motorhome, marine and irrigation. GM made motorhomes
> from '73-8, maybe in all? Casting number appears
> as "231 [tiny 'L'] 788" on the block.
>
>
> so much for a solid rebuild. seems I need to find a new crank. and who knows what else. I will do some research and be in touch. thanks
>
> I could have put a diesel in my coach by now.\
>
>
> New photos:
>
> http://www.gmcmhphotos.com/photos/engine/p67122-engine-castings.html
>
> http://www.gmcmhphotos.com/photos/engine/p67123-engine-castings.html
>
> http://www.gmcmhphotos.com/photos/engine/p67121-engine-castings.html
>
>
> block casting under heads: 33M730673
>
> 3= oldsmobile
> 3= 1973
> M = Lansing
> 730673= vin of car block comes from
>
> Crank?

--
C. Boyd
76 Crestmont
East Tennessee
 
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