Topic: TAO --- The South Seattle Cafe Project

[timbo750]

I am not expert on this and maybe someone said this before but it looks like there has been a foreign material in there to cause that sort of gouge. Where any of ghd rings broken? Might want to check the sump for metal parts.

[Blackfin5]

brandEn - ditto...no expert but "guess" you caught the edge of an oil ring which broke off.  Are the rings on that piston in tact?

[Jerry Rxman Griffin aka MuthaF'er]

Does that match anything on the upper case? Happen during install?

[Blackfin5]

brandEn, curious - do you have similar gouge marks inside the bore at the same vlock position?

[chewbacca5000]

Those cylinders don't look that bad to me at all.  The piston is a question mark, but should be able to run, but might smoke a little?

[MidnightLamp]

I've seen damage like that come from open intakes and bits of rod bearings. They're definitely from bits of something grinding against the side and are not sticking/nipping wear.

I would not re-run those pistons. Sadly a lot of little things can cause a rod bearing to go. Can be just a lot of pinging, or anything that even temporarily reduces bearing oil flow. That's why you normally set your clearances as even as possible to start with (so when the pressure dips you have all the cylinders eat it a bit before it drops too low).

If it were me, I'd take a hone to the F cylinders and see if they clean up with a few strokes of the hone. If they do, I'd get 'em sized up and try to re-run them with the cruznimage 836 kit (assuming knocking the glaze and damage off gives you decent PTW clearance with the new pistons) and some mods to the cylinder bottom (that way you save the money of getting another set of jugs bored to 836).

[calj737]

Can you post some pics of the underside and intake/exhaust ports of your head? Curious to see the related combustion area if you're willing.

[Retro Rocket]

Brandon, is there a  cruising image kit made specifically for the F3.?  If not you'll end up with very low compression, less than stock due to the K's flat top design compared to the F3's high dome pistons. I would be looking for the cause of your detonation {timing ?} and replace the one damaged weisco piston, its definitely not the fault of the piston, they can be bought singularly...

[MidnightLamp]

Now I'm curious, is that cam tunnel difference an F3 specific thing? I have had a K top end on F2 cases and had no issues =\ I did however run a slipper tensioner, and had to machine out a little bit of the cam tunnel.

[MidnightLamp]

Piston can be had from wiseco directly:
http://www.wiseco.com/ProductDetail.aspx?ItemID=4016M06500&ModelID=116&ModelYear=1978&AppID=6417

Cruzinimage does not seem to make an F piston kit.

[calj737]

Almost looks like #3 was a fair bit more lean than the others from this limited picture. Less build-up on the intake valve, and the carbon on the exhaust looks lighter too.

Wonder if you had a fuel issue on this carb where it was just a bit more restricted?

Retro is probably onto it though, as was your research with ignition/detonation. What do the exhaust ports look like? Consistent with the chambers?

[Retro Rocket]

Just doing a bit of reading on your detonation problem Brandon and it seems the excess heat caused by detonation will cause the problem you have..

The heat caused by detonation made the piston so hot, the rings stuck and the piston seized in the cylinder. You can see the seizure marks on the side of the piston. This damage usually ruins both the cylinder and piston.

Replacing detonation- or preignition-damaged pistons in a customer’s engine may temporarily return the engine to service. But the new pistons will likely suffer the same fate as the old ones unless the conditions that were causing the problems are diagnosed and corrected.
Scuffing is another condition that can damage pistons. Scuffing is often the result of overheating, but loss of lubrication, detonation and preignition can also be contributing factors. When an engine runs hot, the pistons swell. This reduces the clearance between the piston and cylinder walls. The cylinder bore can also distort adding to the problem. If the piston scuffs, it will wipe metal off the side of the piston.
Where the scuffing occurs will give you a clue as to what might have caused it. When overheating is involved, the scuffing will be primarily on the upper ring lands and on the sides near the wrist pins. There may also be oil carbon and lacquer burned onto the underside of the piston indicating it got too hot.

[Retro Rocket]

yup, that's the section of that article I thought was relevant. Definitely sounds like exactly what happened to me. My ring lands are good from what I can tell but my engine was only run for a very short time after this happened so I am sure I prevented a lot more damage from occurring.

Are you near DoctorD at all.?  Might be worth a chat with him if thats at all possible...

[SOHC4 Cafe Racer Fan]

That's a good idea.  Doctor D and Jeff and Twinline seem to have a bit of experience tuning the F.

[brandEn]

Got some more cleaning done on the engine today. Got all the gasket material off and that is the worst part of rebuilds I think. I also sanded the fins on the top end. I have been wanting to do this for a long time but never had the courage. I had a lot of paint chips from all the maintenance I have had to do on this engine so I figured what the hell. I love the way it looks and it only took about an hour. I have been marinating the pistons in Berryman B-12 Chemtool and this stuff is awesome on carbon buildup. The results speak for itself. I have to say though it's tempting to use this #1 piston after cleaning it up but I will listen to the more experienced and replace it as tempting as it is.

[FunJimmy]

Those Pistons cleaned up perfectly.
I'd consider re-using them too.
Nice touch on the fins. I like them polished.

[brandEn]

Hi Jim!

[Retro Rocket]

I was wondering how that piston would come up after a clean, I would probably use it too but i think i would go with a low friction coating on  the skirts just to make them a little more slippery....   How were the rings on that piston Brandon..?

[Retro Rocket]

Rings were perfect as far as I could tell. I sanded the skirt a bit but not sure if that will effect the weight/balance/strength at all...

If you were racing maybe, on the street, i doubt it.... Once again i would run all this by Dave {doctorD} or Mike Reick...

[FunJimmy]

Rings were perfect as far as I could tell. I sanded the skirt a bit but not sure if that will effect the weight/balance/strength at all...

Hi Branden. 
You'd need to sand the crap out of them to adversely effect the weight/balance/strength of a forged slug like those and that would screw up the clearances too. Doubt you did any harm there. Like the Rocket said.......if racing, but not on a street scoot.

[Davez134]

Got some more cleaning done on the engine today. Got all the gasket material off and that is the worst part of rebuilds I think. I also sanded the fins on the top end. I have been wanting to do this for a long time but never had the courage. I had a lot of paint chips from all the maintenance I have had to do on this engine so I figured what the hell. I love the way it looks and it only took about an hour. I have been marinating the pistons in Berryman B-12 Chemtool and this stuff is awesome on carbon buildup. The results speak for itself. I have to say though it's tempting to use this #1 piston after cleaning it up but I will listen to the more experienced and replace it as tempting as it is.



Those fins look great! what did you use to sand them with?

[brandEn]

Hi Dave just used my die grinder and some sanding discs. Finished off with some scotchbrite pad. Went pretty quick for such cool results. Now I dont need to repaint!

[SOHC4 Cafe Racer Fan]

Great look with the sanded fins.

[brandEn]

Thanks Don. I just hope I can get her to be a reliable lump now!

[calj737]

Do you happen to have a digital scale to weigh the pistons? Can't imagine you've taken enough mass off to significantly alter its weight. +1 on treating the slugs with DFL and Cermet. The Cermet especially will help defend against the pre-detonation damage and heat transfer to the rest of the slug.