Topic: Would you run this piston

[brandEn]

My CB750 F3 suffered a tragedy and I was hoping to get some input from the HiPo section. If you want the details you can read my TAO build thread. But the reason I am posting here is because I was wondering if anyone can tell from the pictures if this piston is serviceable? It's a Wiseco 836 piston for an F3

[Jerry Rxman Griffin aka MuthaF'er]

Good question. It's what you may not be able to see that might bite you in the ass. Such as cracks. While the skirt damage looks fairly benign and could be cleaned up/sanded perhaps, what if there is a crack in that body or one of the ring lands?

Me, I might be tempted to clean it up and hope for the best provided I could see no more damage.

However consider Johno's racer. His piston self destructed which may have been caused by an unseen fracture after it fell off the table??

Maybe Wiseco could inspect it or replace it.

[Jim F]

you could send it to me and let me laser weld it
if there is a crack it will show up in the process
and because there is minimal heat, nothing else will be affected
just let  me know if you want to try this
Here is a float tower that I welded with this process

Jim

[brandEn]

I will consider that. Whats the cost?

I was hoping somebody would pop in here and say heck yea run it!

[Jim F]

I would think you could take some scotch bright  and polish it out
as far as there might be some cracking, not sure about that but it would show up
under the laser
45.00 dollars plus shipping
Whats a new piston cost?

Jim

[dragracer]

How does the inside of the bore look? Is the cylinder scarred at all?

[brandEn]

It was scuffed a bit but I hit it with scotchbrite real quick and to me it doesn't look bad but I don't have the experience to know for sure.  Seems like a good hone job and the cylinder will make it.



After hitting with scotchbrite. 2 o'clock position in the picture.

[dragracer]

It was scuffed a bit but I hit it with scotchbrite real quick and to me it doesn't look bad but I don't have the experience to know for sure.  Seems like a good hone job and the cylinder will make it.



After hitting with scotchbrite. 2 o'clock position in the picture.

Agreed, a good quick hone, new rings and you'll be okay for a while in my opinion.

[TurboD]

After a good checking and removing any high spots on the piston skirt, I would have no trouble reusing the piston. I would hone the cylinder with a rigid hone, to again remove any high spots and to be sure it is good and true.

[demon78]

I would be more concerned about the cylinder than the piston and if your really worried about the piston you could get it Zygloed at an engine shop where they did Magna Fluxing and Zyglo, I have no idea what they would charge in this day and age, I would find a bike lover in one of the aero engine overhaul shops and have him throw it in with a job.
Bill the demon.

[bear]

I might be missing somthing here but surely pistons arn't that dear over there.
If the bore does not not come up with a hone an oversized piston is an option.
If the motor is on the bench, why put it together so that it's only "good enough".

If I was at a race meeting would I  clean it up and run it? Yes.
If I had it on the bench? No.


Cheers,
Brian

[MidnightLamp]

That was my thought on it. It's $150 or so for a new piston with rings and pin. You could probably have them measure up a few and get you one on the bigger end of things and get your cylinders honed somewhere that uses a diamond hone or other nice rigid hone and hope that 5-8 tenths clears it up and puts you within a reasonable range of PTW clearance.
 
If it were me personally, I wouldn't run it considering how much wear on the side of the piston there is. Even if not hugely noticable, a drop in compression (slightly) or a change in oil consumption on only one cylinder is not something especially on a pushed engine.

[brandEn]

I will buy a new piston and a full set of rings. I will take it to an engine machine shop and have them hone it and look things over. I really appreciate the input everyone and you got me pointed in the right direction.

[cherbear]

If you can afford it, May as well have them all honed so the motor runs evenly. that one being easier to push will most likely eventually cause a problem. I second a new piston.

cb750 k6

[faux fiddy]

I second a new piston.

cb750 k6

If you're racing it absolutely new piston. If you're planning to dump this bike, tap the high spots down instead of grinding on it. Thow it together and make it start and be a PO.