Topic: Well, the bike didn't make it to the mechanic today. PROBLEM FOUND 5/25

[Phoenix]

Same thing happened to me on 3 and 4.  Had the carbs re-built using 120 jets like before.  Also re-bilt the oil pump.  Got jugs from Bill Bennet and put a set of bored sleeves in with another set of cruzinimage 836 pistons.  Didn't us MLS gasket this time.  Got about 3000 miles on it and working great.  Good Luck.

[Dolomite]

Same thing happened to me on 3 and 4.  Had the carbs re-built using 120 jets like before.  Also re-bilt the oil pump.  Got jugs from Bill Bennet and put a set of bored sleeves in with another set of cruzinimage 836 pistons.  Didn't us MLS gasket this time.  Got about 3000 miles on it and working great.  Good Luck.

If I do rebuild, I plan on doing Wisecos.

[scottly]

Please post pics of the pistons once the motor is torn down.

[754]

Yes, to the plugs. And engine is already bored to 836, so if the cylinders can't just be honed, the question is which is easier/ cost effective: resleeve the 836 or bore over to 890?

850 makes most sense for a tired unscored 836, small amount to take out, cheaper that way.
 890 probably involves sleeves and boring the cylinder with sleeves out, then fitting pistons.
 But first find out the cause, all 4 plugs having bits on it is leaning towards timing issues, but you have to find out.....
 Because I have heaped tons of abuse on cast 836 pistons that lasted a really long time

[scottly]

Inspect the porcelain around the center electrode of the plugs carefully; chipped porcelain indicates detonation or pinging.

[Dolomite]

And here they are, pictures are in. See if you can spot the issue on the piston.

Head should clean up, cylinders need to be redone. CycleX sells the 836 sleeves for 129, but they require boring to 74mm (900) and that alone could cost 400. Does anyone know of a good source for 850 pistons if I went that route? I'm a big fan of CycleX products but their pistons are very pricey compared to Wiseco.

[PeWe]

There are old bad looking but cheap cylinders on eBay with OK sleeves to use.
Or a complete good looking stock cylinder to bore to next size or 836.
If taking sleeves from another cylinder, check correct version. Later has holes drilled at top.

[Dolomite]

Spoke to guru Ken over at CycleX, he said choosing to redo old cylinders vs pick up used ones is a wash. I'm going to pickup the cylinders this week from the mechanic to take over to a machine shop for them to measure and see what needs to be done as they will know best.

Ken did say as far as melting pistons in addition to the lean condition to definitely check the timing as that's the only time he's seen melting pistons.

[Dolomite]

There are old bad looking but cheap cylinders on eBay with OK sleeves to use.
Or a complete good looking stock cylinder to bore to next size or 836.
If taking sleeves from another cylinder, check correct version. Later has holes drilled at top.

I'm looking at a set of 77s for ~40 with shipping, but want to get mine over to a machinist first to see what they think as far as work needed.

[754]

You have not showed your cylinders , is the holed piston one badly scored ?

[ekpent]

Gnarly.  Looks more like a two stoke disaster then a Honda 4.

[Dolomite]

You have not sowed your cylinders , is the holed piston one badly scored ?

Didn't get any pictures of the cylinders, I'll ask the mechanic to snap a few and send them over.

[PeWe]

I melted my first 836 set 1984. Cyl 2-3 pistons, hole in one, a bump in the other. Replaced all 4 pistons with a  new set, honed cylinders, replaced a few bluish guides and all 4 rods that had bluish ends. Maybe a valve or 2 too.
Probably ignition wrong.

Compression rather high (RC pistons shaped for head and vice versa) for fun wheelies but extra sensitive if neglecting timing.

I fixed another old stock cylinder last year, rusty with stock bores I thought were OK for 61.5mm pistons. 2 bores were not good enough, too deep marks after the rust.

Visited a friend that had several sleeves he has taken from ugly damaged cylinders.
Back to the shop that swapped the sleeves (later model with wider oil return holes enter the sleeves that must match the holes in block).
Bored correctly for 61.5 mm CI 392 pistons.
No extra charge for sleeve swapping. He is used to do it quick with a propane torch.

Same guy that fixed my 836 1984, ported and bored it the year before and done more head jobs last years
He will soon retire so I have to  through a head job at him asap.

[Dolomite]

PeWe, I have been scouring Google for a set of stock sleeves sans the jugs but cannot find any. Perhaps you have some stock sleeves lying around that would be good candidates for a 836 bore?

[Dolomite]

Here are the cylinder pictures I just received.

[PeWe]

PeWe, I have been scouring Google for a set of stock sleeves sans the jugs but cannot find any. Perhaps you have some stock sleeves lying around that would be good candidates for a 836 bore?

I live in Sweden so it will be easier for you to find a cylinder on eBay USA.  I have seen many not long ago.
You can use rusty stock cylinders for 836, 65mm.

Here a cheap one for sleeves
https://www.ebay.com/itm/382870612214

Another one, also later with sleeves for wider oil return holes.
https://www.ebay.ca/itm/264295549656

[bryanj]

Cylinders dont look too bad, may well clean.
Used to have a stock of those special low compression pistons, 80% timing, valves and crowns dont look that lean

[Dolomite]

Cylinders dont look too bad, may well clean.
Used to have a stock of those special low compression pistons, 80% timing, valves and crowns dont look that lean

That's what I am hoping. Going to try to pick them up after work today and then take them to a machine shop for inspection later this week/ weekend

[PeWe]

One look a little bit scratched.

[scottly]

Yes, to the plugs. And engine is already bored to 836, so if the cylinders can't just be honed, the question is which is easier/ cost effective: resleeve the 836 or bore over to 890?

Those pistons are standard, stock pistons, not big bore. Notice the STD stamp?

[scottly]

The broken ring land on the #1 piston is usually caused by insufficient ring gap; when the ring expands with heat, the ends butt together which forces the ring tightly against the cylinder wall, creating friction and more heat.

[Dolomite]

Yes, to the plugs. And engine is already bored to 836, so if the cylinders can't just be honed, the question is which is easier/ cost effective: resleeve the 836 or bore over to 890?

Those pistons are standard, stock pistons, not big bore. Notice the STD stamp?

I know what the stamp says, but I have the receipts showing the bore over to 65mm and the 836 piston. There's a reason they came in a white box, and the next set will be Wisecos

[scottly]

When you pick up the cylinder block, grab at least one piston, and see if it says "ART" and/or "392" on the side near the pin.

[Dolomite]

Will do.

[bryanj]

STD 350 pistons? That was the original big bore kit