Crank with incorrect conrods

[CFS]

Hi,

Last year whilst working in the UK I had my GT380 crank refurbished by a reputable company.
Over the Xmas break I stripped my motor, replaced the crank and then noticed that the small ends of the conrods are the incorrect size. The centre to centre dimension seems to be correct at 110mm.
Presently the small ends are 21mm diameter and should be 18mm diameter.
I know that replacing the conrods is the best option, but due to working outside the UK for the foreseeable future I
am finding it impossible to send the unit back for repairs due to customs documentation required by all couriers which I cannot provide.
My question is if there is an alternative solution to replacing the conrods?
Can a bush be machined and pressed into each small end?
I hope this is a possible solution. Await input from the forum members.

Thanks
Carlos

[Alan H]

It appears that the company was less reputable than they make out to be.
Trouble with fitting bushes in the little ends of the crank is that the con rod weights will change and will affect the balance of the crank. It needs doing properly. Have you contacted the company about the problems?
Just a thought, are 'thicker' needle roller sets available? All my triples are 550s, so I've little knowledge regarding 250/380s other than they are 54x54mm bore & stroke!
Dollydog is the one for those.

[markush]

They probably installed connecting rods from T250/GT250KL, which have 16mm piston pins and 21mm connecting rod eyes.
Suzuki switched to a 14mm piston pin starting with the GT250M model and from then on the same connecting rods were used in the GT380 and GT250MABC.

So you could switch to such pistons with 16mm piston pins.
for example these ones with standard 54mm diameter:
https://www.cruzinimage.net/2017/08/10/ ... size-16mm/
Other sizes and the right small end bearings you'll find there too.

The lucky chance for hefty tuning.

I wouldn't recommend bushings.

[CFS]

Hi Alan, Markus,

Thank you for your valued input.
The crank was refurbished by a reputable company. They have done endless cranks and have a good reputation even on this forum. Unfortunately even for good companies things still go wrong at times.
I have contacted them and they have offered to replace the incorrect parts, but the problem is getting the unit across to the UK. This is proving to be impossible due to the required customs documentation.

You both mention the possibility of using larger gudgeon pins (16mm) but, unfortunately that is not an economically viable proposition for me, as I've recently rebored to 1.5mm oversize and only done around 500km since the rebore.

I was really looking for a quick and simple fix but as we all know that is non-existent.
Are there any other possible options?

Thanks
Carlos

[markush]

... using larger gudgeon pins (16mm) but, unfortunately that is not an economically viable proposition for me, as I've recently rebored to 1.5mm oversize and only done around 500km since the rebore.

I assume, by this you mean that you would need new cylinders in addition to the other pistons in order to cope with the available original oversizes.
That would actually be expensive.
But I'm afraid it won't work without using 16mm piston pins.

However, there are also aftermarket pistons with 16mm piston pins for GT250KL in 1.5mm oversize, which would fit.
I use these in my GT250 racer.
The piston manufacturer is GPM, Italy. (Piston #5422A)

Another option would be to have the piston pin eyes of the existing pistons fine reamed to 16mm by a suitable company. Of course, the grooves for the piston pin clips then also have to be reworked.

[CFS]

Hi Markus,
Thanks for the information.
Can you please provide me with your suppliers website so I can ask for availability and prices? I assume that they sell their piston kits individually as I would need 3, and are based in the EU.
Would the clearance for these pistons be the same as what I already have or would the bores need re-honing in your opinion?

Thanks
Carlos

[markush]

I got the GPM #5422A pistons here:
https://www.duempert-kolben.de/

It is a German company that specializes in pistons.
They could also help you if you need a customized piston.
Or they are looking for a piston from their stock based on your measurements or samples.

good luck

Since I use these pistons in my racer, a longer break-in period is not possible. That's why I machined the cylinders to 0.06...0.07 mm piston clearance.
For use with running-in according to Suzuki regulations you can use the normal installation clearance of 0.045...0.055mm.
The general rule of thumb for piston installation clearance is:
Installation clearance in mm = piston diameter in mm / 1000


edit:
just found IMD pistons: https://www.ebay.de/itm/166524039513

[CFS]

Hi Markus,
Thank you.

I will contact the suppliers and hopefully have a solution soon.

Carlos

[Alan H]

Any news on this?

[CFS]

Hi Alan,

Yes, I think so. IMD Pistons were able to source GT380 compatible pistons with a 16mm gudgeon pin.
These have been ordered so hopefully this can be put to bed.

As for the crank bearings not having the locating pegs is another issue I'm still trying to resolve.

Cheers
Carlos

[markush]

It is not impossible to subsequently drill the holes for the pins in the bearings. All you need to do is find someone who has the appropriate tools and is willing to do the work on the mounted bearings.

[CFS]

Thanks Markus.
I am reluctant to drill out the bearings on an assembled crank. The swarf will end up in the big ends, seals and main bearings. Washing the crank won’t guarantee that all the swarf has been removed. I’m more inclined to use some bearing glue or similar to hold the bearings in place.

[markush]

Hi...

Any news here?
Do you got the engine running again in the meantime?

[CFS]

Hi Matkus,

Yes, I installed the new crank & pistons but it didn't go well.
I couldn't get the leak down test to hold pressure very well and had issues securing the bearings, so I am currently changing back to the old crank and pistons.

This link shows what the pistons looked like when I opened the motor as well as other issues I had.
viewtopic.php?f=5&t=15203

Any idea as to what may have caused this?

Cheers
Carlos

[markush]

Any idea as to what may have caused this?

not really...

but if the leak test shows a leak, I would look further in that direction, because you have already checked and ruled out the ignition system and carburetor.
Either the crankshaft seals, although new, are leaking or they may have been jammed during installation.
Another possibility is that the crankcase itself is leaking because the housing halves are not sitting together properly, perhaps due to the use of bearing adhesive.
But from a distance, this is all speculation.