Author Topic: Is this piston/chamber ok? (Read 4217 times)

Ira · « **on:** November 10, 2013, 05:00:21 pm »

I'm in the midst of a top end job, and one of the items I'm sorting out is this strangely marred piston surface. It looks like something hard was bouncing around in the combustion chamber for a long time.

Are the piston and head ruined, or is this only cosmetic? Should I only replace one or the other? These are aftermarket 65mm pistons of unknown origin. If I had to replace one, can anyone tell me what they are?

The others look like this:

Thanks guys!

mrtanner101 · « **Reply #1 on:** November 10, 2013, 05:20:15 pm »

I personally would not reuse that. with knowing that something serious happened to it i.e. the massive damage to its entire surface I wouldn't be surprised if it broke apart at sometime. and even if it didn't is risking the rest of the engine worth the money your saving by not replacing it now?

thirsty 1 · « **Reply #2 on:** November 10, 2013, 05:20:51 pm »

It looks like the valve seats are ok. Previous falure? Did it run ok before you took it apart? If the seats are ok I'd clean up the head lightly with some sand paper (temporarily reinstall the valves) and run it. Don't hit the seats with the sand paper it'll ruin them. I'd inspect that piston with a magnifying glass looking for cracks. If it's ok I'd do the same sandpaper routine. If your not comfortable running any of the parts then don't do it. Piece of mind is worth a lot.

I'd say a chunk of valve or spark plug was beating around in there.

My 2 cents

Ira · « **Reply #3 on:** November 10, 2013, 05:26:12 pm »

It ran fine before I took it apart. I'm remedying some oil leaks. I have no problem cleaning up the head with sand paper and replacing the piston, but that brings me to the second issue: what pistons do I have?

madmtnmotors · « **Reply #4 on:** November 10, 2013, 05:29:10 pm »

It might be a shadow (or carbon?), but the deepest part of the valve recess (left side) in the piston above looks like a crack in the piston.

thirsty 1 · « **Reply #5 on:** November 10, 2013, 05:29:55 pm »

Quote from: Ira on November 10, 2013, 05:26:12 pm

It ran fine before I took it apart. I'm remedying some oil leaks. I have no problem cleaning up the head with sand paper and replacing the piston, but that brings me to the second issue: what pistons do I have?

Cant help you with the brand?

Ira · « **Reply #6 on:** November 10, 2013, 05:40:48 pm »

Quote from: madmtnmotors on November 10, 2013, 05:29:10 pm

It might be a shadow (or carbon?), but the deepest part of the valve recess (left side) in the piston above looks like a crack in the piston.

that's carbon. it was really hard to get it all off of that one, with the weird texture.

These were installed by a previous owner. The outside says "AP" and the inside casting says "+1".

ekpent · « **Reply #7 on:** November 10, 2013, 06:22:56 pm »

http://www.ebay.com/itm/New-Set-Honda-CB350-CL350-SL350-Piston-Ring-Kit-1-00-/350906177162?pt=Motorcycles_Parts_Accessories&hash=item51b3a3568a&vxp=mtr Just guessing here but it may be a 1 over cb350 piston, an older way of doing a cheap big bore.

Powderman · « **Reply #8 on:** November 10, 2013, 06:30:01 pm »

You will lose considerable compression in that cylinder if you sand both the piston and chamber to smooth them out. For sure I would not reuse that piston, don't know if the head is worth saving.

Trad · « **Reply #9 on:** November 10, 2013, 06:44:22 pm »

Personally I wouldn't run either. With all the cylinder head pitting you risk a larger chance of carbon build up and pre ignition. At very least sand the high stop off both with 400 and 600 wet. Don't go too hard or like others said, you will loose compression. Try and salvage some better condition healthy parts.

thirsty 1 · « **Reply #10 on:** November 10, 2013, 06:48:45 pm »

Quote from: Powderman on November 10, 2013, 06:30:01 pm

You will lose considerable compression in that cylinder if you sand both the piston and chamber to smooth them out. For sure I would not reuse that piston, don't know if the head is worth saving.

Indeed you would lose comp. if you sanded it smooth, but I also wouldn't sand it all down till it was smooth. I'd just take the high spots off. That hole has been repaired and according to Ira the bike runs fine. Same goes for the piston. Just a nice light sanding. It sounds like he's fixing leaks.

Ira · « **Reply #11 on:** November 11, 2013, 10:41:33 am »

Daytime crew, any idea what kind of piston I have?

lrutt · « **Reply #12 on:** November 11, 2013, 11:43:25 am »

depends on what the intended purpose is. If you just want to get it together for a runner, not a good resto or anything. Just a weekend bomber. I'd just clean them up and use them. If you are putting some bucks into a good resto though or plan on doing some serious riding with it you might change out the piston. If the valve seats are good I'd clean the head up and use it myself. Those pits don't look too bad. Hell I've raced worse than that on my old Yamaha flat tracker after it ate a ring. And that thing lasted several more seasons before I sold it off. Just put a new piston in and cleaned the combustion chamber up.

lucky · « **Reply #13 on:** November 12, 2013, 09:49:03 am »

You better get some help.

That cylinder head IS reuseable as long as the seats are not damaged.
Sometimes you can get new seats.

You cannot just use any piston. It must be the correct piston for that engine.
The year of the CB750 and the piston needs to match.
The piston Must fit the bore.
The bore must be measure at the top and bottom. No ridge.

That damaged cylinder head can be smoothed out a little with a dremel and the CORRECT sanding disc. DO NOT TOUCH THE SEAT!

Ira · « **Reply #14 on:** November 12, 2013, 12:19:23 pm »

lucky - thanks for the advice. the engine is from a '75 K. the block was bored to 836 by a PO. i've had it professionally measured, and it is in correct spec, both round and taper. the pistons are 65mm, which fit the bore.

i'm not sure if you read this entire thread, but i'm asking if anyone can identify this piston, because i've been advised to replace it. do you have any insight into the manufacturer and model?

martin99 · « **Reply #15 on:** November 12, 2013, 12:23:51 pm »

ART Pistons is my bet. I've had a look around the net and can't find any images the same to confirm it though. Might be worth contacting them and ask?

wrenchmuch · « **Reply #16 on:** November 12, 2013, 12:27:47 pm »

That could be an Arias piston. No longer available if it is. Is it 65mm?

Ira · « **Reply #17 on:** November 12, 2013, 01:15:25 pm »

Quote from: wrenchmuch on November 12, 2013, 12:27:47 pm

That could be an Arias piston. No longer available if it is. Is it 65mm?

Yes, it is 65mm.

lucky · « **Reply #18 on:** November 12, 2013, 04:38:30 pm »

Quote from: Ira on November 12, 2013, 12:19:23 pm

lucky - thanks for the advice. the engine is from a '75 K. the block was bored to 836 by a PO. i've had it professionally measured, and it is in correct spec, both round and taper. the pistons are 65mm, which fit the bore.

i'm not sure if you read this entire thread, but i'm asking if anyone can identify this piston, because i've been advised to replace it. do you have any insight into the manufacturer and model?

Who know where it came from. Can you contact the PO?
Some pistons have offset wrist pins. That is a consideration.
Is there a arrow on the top of the piston so you know which way to get the offset installed correctly?

ekpent · « **Reply #19 on:** November 12, 2013, 05:04:45 pm »

The reasons I thought they may be cb350 pistons is because they were used for big bore kits at one time and also you mentioned that the piston was also marked on the bottom "+1". Here is a +1mm cb350 piston that measures 65mm. Again just a hunch as 65mm was and still is a pretty popular size for kits. The folks over in the Hypo section of the forum would be the ones to really ask that question. http://bore-tech.com/product/pr650

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Author Topic: Is this piston/chamber ok? (Read 4217 times)