GT380 crank bearings

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CFS
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GT380 crank bearings

Post by CFS »

Hi,

My crank has been refurbished but the bearings don't have the locking pin/pegg to lock their position between the 2 motor halves.

Will this be a problem or will they clamp in place once the 2 halves are torqued together?

Thanks
Carlos
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jabcb
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Re: GT380 crank bearings

Post by jabcb »

Sorry, but I have bad news.

The oil pump feeds oil directly to the those crank main bearings. Look at the main bearings & you will see the hole for the supply of oil.

That hole must align with the holes in the top crankcase half that feeds the oil. The pins guarantee that they line up correctly.

Without those pins, the odds are high that one or more of those holes do not line up correctly. And the main bearing won’t last very long.

Do your bearings have the oil flow hole & the hole for the pin?
If so, you may be able to get the shop to install the pins from used bearings.
If not, you have the wrong bearings.
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CFS
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Re: GT380 crank bearings

Post by CFS »

Hi Jbacb,
No, I don't recall seeing any holes.
I remember seeing the locking pins/pegs but don't recall seeing any holes in the bearings top side where the oil supply comes in.
Do you have a photo/picture so as to compare?
I also don't believe that there are any holes on the new bearings.
Is there an alternative to use pre-mix in lieu of the oil pump?

Thanks
Carlos
karl pa
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Re: GT380 crank bearings

Post by karl pa »

No you can't use premix and not oil pump. The crank has oil guide plates that pull oil from main bearings and not allow premix to reach the main bearings, causing them to fail.
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Re: GT380 crank bearings

Post by sportston »

Karl is right. Don’t use premix!
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jabcb
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Re: GT380 crank bearings

Post by jabcb »

Sorry, a bit of confusion on my part.
I recently rebuilt a T500 motor & did a GT550 a while back. Never did a GT380 motor but it is similar to a GT550 motor.

The T500 bearings have oil flow holes.

The GT550 bearings do not have oil flow holes.
Pic of the GT550 crank. Oil flow is between the bearing pairs. And Between bearing & oil seals.
Image

The GT550 crankcase has little notches for the bearing pins.
Image
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markush
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Re: GT380 crank bearings

Post by markush »

Hello...

I have two removed GT380 crankshafts lying around, so I took another look.
The main bearings have no holes other than those for the pins.
The 2-stroke oil is pumped through the gaps between seal rings and bearings. The gaps are ensured by knobs on the sealing rings.

The pins prevent the outer rings of the bearings from rotating.
As an emergency solution, you could try to attach the bearings with bearing glue (Loctite etc.) instead of the pins. (This is really just a theoretical workaround; I haven't tried it and actually wouldn't recommend it. It might work, but later, when you have to open the engine again, you'll have the problem of removing the adhesive residue. Plus, the adhesive, as opposed to the pins, may prevent the bearings from the minimal axial displacement they may experience due to thermal expansion of the crankshaft.)

The bearing on the right must also have a groove for the C-ring in the correct position. Is this groove even there and does it fit the crankcase?

As mentioned from pre writers, driving with premix doesn't work for long.

Edit: OK jabcb was faster :mrgreen:
CFS
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Re: GT380 crank bearings

Post by CFS »

Hi all,

Thanks for the replies and advice.
The question about the premix was as a last resort and only to find out if someone had done it successfully and what it entailed. Like everyone else I prefer the pump option.

Jabcb & Markus - thanks for looking into your cranks/projects and confirming that the bearings have no oil holes.

Unfortunately, my bearings don't have the pins so an alternate solution is required. The right hand side bearing does have the groove for the c-ring in the correct position. The crank was installed, everything sealed up and rotated freely.
When next home I will assemble the two halves and torque the bolts down. I will measure the bearings and also the bearing openings within the two halves and assess if there is adequate tolerance available to hold the bearings in place.I certainly hope so!

Once again thank you all for your valued help.

I'll keep you posted of my findings.

Carlos
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