GP engine rebuild - parts required

1940 - 1941 BRC, MA, GP, Preproduction Prototypes. Knowledge Base NO EBAY or COMMERCIAL SALES.

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CM1
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GP engine rebuild - parts required

Post by CM1 » Wed Dec 06, 2017 1:02 pm

Hi all,

I have recently acquired Ford GP 9251 and am undertaking what will be a very lengthy restoration, judging by the amount of parts missing!

I am currently working on the engine and hope someone can help me with the below.

The original pistons are in good condition, so I would like to reuse them, but need to buy new piston rings (3 per piston). Does anyone have any NOS piston rings for sale? If not, will the ones out of Ford Tractor 9N engine overhaul kit be compatible, or do you know of any other ones which will work?

I also need a full valve train kit - does anyone have a set in good condition for sale or should I buy a 9N set?

I am also looking for a set of original GP wheels (4" rim width) - if anyone has a set in good condition, please PM me.

Any help would be much appreciated!

Thanks

Clive Manners
Somerset
UK


Michael C
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Re: GP engine rebuild - parts required

Post by Michael C » Sat Dec 09, 2017 7:41 am

There are a number of choices. I used:
9N mains and rod bearings;
9N valves with single-piece valve guides and adjustable lifters (you need the special tool to hold them in order to adjust the clearance);
3-3/16inch V8, 4 ring pistons and rings. The block was sleeved back to standard, but you could use oversize V8 pistons. On another thread, someone (cannot remember who - person with more knowledge than me!) confirmed the V8 pistons were an authorised replacement part.

Replaced the oil pump gears and timing gear with new 9N items from tractor parts supplier like Davis or Steiner. Gasket set also from a 9N tractor parts dealer.

Mike

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Re: GP engine rebuild - parts required

Post by Wolfman » Mon Dec 11, 2017 6:43 am

Hi Clive.
Not sure who to direct you to in the UK.
I use All State Tractor Parts. Tractorpartsasap.com. They have multiple stores around the mid west, USA.
They should have everything you need for the engine. Except the manifold. 9N tractor used an up draft carb. set up.
I just bought a complete valve train kit for an 8N from them. Complete. Valves. guides. springs . retainers and keepers. The adjustable lifters are separate, sold by the piece. Not a set, but well worth the cost. You know what I mean if you have ever tried to adjust the valve clearance with non adjustable lifters. And be sure to buy the adjusting tools ( 2 of them. left & right) Mike referred to. You will need them.
The tractor used dry sleeves in the cylinders. I am thinking a GP engine would be the same. But won't swear to it. Just pull the old sleeves and install new ones. Made that sound easy, didn't I !
The original tractor engine had 4 ring pistons. The newer and replacement pistons are 3 ring. Makes me think your engine may have been rebuilt before. Just the rings are available.
Oil pump. This could be a big one. The oil pump and front main bearing cap are one piece. When the oil pump body is worn beyond limits, the front main bearing cap/oil pump body has to be replaced. This is usually the case on an original, 60 year old oil pump. The pump does not come complete. The gears are sold separate. I did not have any trouble finding the oil pump rebuild kit but the Cap/Oil pump body was a big one. NLA ( No Longer Available ) kept coming up. All State Tractor finally found one for me but it was not cheap. None the less, I was really glad to get it.
Good luck with your project, and welcome to the "G".
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB

Michael C
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Re: GP engine rebuild - parts required

Post by Michael C » Mon Dec 11, 2017 3:28 pm

As Wolfman said, the oil pump body is part of the front main bearing cap. I only chose to replace the gears as the body was fine - only to find later that someone before me had replaced the front main bearing cap/oil pump, and it was a whisker out of alignment for my motor (ie a non-matching cap from another engine). Fine when the bearings were worn, but when I had the crank ground and put in new bearings, it was tooooo tight. Had to have the main bearing caps line-bored, so be careful of that potential problem.

A GP engine is not ordinarily sleeved, but to bring it back to standard from oversize, you can have it bored and insert tractor sleeves, which is what has been done to my engine. Hence, I was then able to use new manufacture 3-3/16inch standard, 4-ring V8 pistons and rings, which are readily available (I have half a set, ie 4, with rings, spare from my re-build, as the pistons/rings were only available in a set of eight).

Good luck.

Mike

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Re: GP engine rebuild - parts required

Post by CM1 » Tue Dec 12, 2017 9:16 am

Hi Mike and Mike,

Thank you very much for the information and advice you have given me. I will definitely talk to the engine company who are remachining the engine parts, to ensure they have looked at the oil pump assembly fully.

Unfortunately, the previous owner(s?) had rebuilt the engine with the original block which had been tig welded to try and fix the cracks due to lack of anti freeze at somepoint.

As you can see below, it looked like a "snail trail", so I decided to start again and have the block fusion welded by a specialist who works only in cast iron. However, the fusion welding can distort the bores and other seats for valves, cams etc, so it is now with the machining company to remachine where necessary.

I am hoping the 9N piston rings are the same thickness as the ones on my current pistons, to save me having to buy new pistons.

Thanks again for your help and advice and I will keep you posted!

Cheers

Clive
GP block after fusion weldingJPG.jpg
GP Block prior to work.jpg
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Wolfman
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Re: GP engine rebuild - parts required

Post by Wolfman » Wed Dec 13, 2017 7:51 am

Very impressive repair !!
Mike Wolford
CJ-2A
VEP GPW
Comm./Inst. SEL
AOPA ( 50 yrs)
EAA ( 49 yrs)
4th Inf. Div. - 5th Inf. Div. - 2nd Armor Div. - CIB


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