Topic: Cylinders

[lash]

Need opinions on if this is salvageable. I picked up these cylinders and really didn’t notice how much has been machined off the top. At least I think that is what has happened. When I put an engine together it made some noise I wasn’t happy with and took it apart to find that the pistons may be contacting the gasket or head.
Brand new piston and you can see the contact on the top front.
Any way to work around this?

[madmtnmotors]

Yep, good reason to check piston to deck height before installing the head. A couple of spacers on top of the cylinders and tighten down (hand tight is fine for this exercise) at a couple of the cylinder studs so the cylinders stay put to rotate the crank to check piston to top of cylinder deck before installing the head. The top of your cylinders have been machined far enough that the recesses for the oil feed o-rings is gone at the two rear studs next to the cam chain tunnel. You can use a thicker base gasket and have new recesses cut for the oil feed o-rings. Others should be able to tell us the stock deck height (i.e. "cylinder height" from bottom gasket surface to top gasket surface) so you can measure yours to determine how much was cut. Hondaman ought to know that dimension off the top of his head.

[calj737]

It would have been very advantageous to measure the piston to deck before disassembly. Once you get that measurement, gasket thickness or piston relief machining can be ascertained. It could also be the cam causing the valve travel, so that should also be checked.

[BenelliSEI]

Are the pistons oversize? Bore of the head gasket too small?

[PeWe]

Stock cylinder height 85.0mm on my cylinders.

Is there any lower round areas for the 2 o-rings for oil to head?
Depth around 0.9mm.

If pistons outer part sit flush with head surface at  TDC without base gasket is good

My 970cc cylinder had to be milled 1.0mm (84.0mm)  to match the pistons outer edge for squish despite thin base and head gaskets.
This before sleeves went in. Shop had to mill for the sleeves flanges and redo the 2 o-ring seats that disappeared.

(Piston crowns milled too, forged with lots of meat at top)

[Honda Hansel]

Hi
Looking at the pictures
Check the pistons for damage to the Ring groove
Get a new cylinder and start over fresh

Yes it cost and that sucks
spending extra Dollars on some thing that is not right to me doe's not make sense

Honda Hansel   

[lash]

I’m with you HH. Too many negatives to save this, just going to start over with different cylinders.

[HondaMan]

I've got several 836cc-bored cylinders, decked and ready to go, if you're going that route. The owners bailed on the 836 approach AFTER I had them bored.
The normal decking for these cylinders is 0.010", and it can be done twice (like my own engine) but no more, UNLESS the cylinders happen to come from a late (last 2 months or so) K4 or K5 engines made before about 3/75. Those unique cylinders were 1mm taller (in US bikes, not so sure about others) to lower the compression slightly while the USA was having severe gasoline shortages: Honda jumped in with a quick change to improve MPG (to an advertised - but optimistic - 50 MPG figure), but those bikes would also not reach over 100 MPH. It didn't slow sales much, though, as US speed limits being at 55 MPH then didn't strain the bikes.

I have also variously had the shoulders of the pistons turned down. This cost me about $100 at the time, when getting pistons for these bikes was tough for a while. I used some from the 1979-80 CB750 DOHC4 engine, turning the piston shoulders back about 2mm (these are +1mm oversize, too, for the SOHC4 engine, making it 760cc). I still have some of those pistons around here, too. The final compression numbers were like 155-165 PSI, too, and it really crackled into its 4-1 header. That bike is still just south of me here, in a townhouse garage. It is a K7.

[PeWe]

Forgot to mention, my 970cc cylinder got the dowel pin holes adapted too.
I always measure the depths on both sides so right dovel lenghtcan be used.

Case- cylinder and cylinder-head.
The dowels have different lengths during the years too. Check CMSNL.com

Not fun to realize that bottom dowels case-cylinder  or cylinder-head are too long when engine is completed.
They need to be a little shorter than mating sides total. Or seat it in case, measure the remaining lenght (stick out).

That lenght should be same as cylinder hole. Test with a dowel pin and measure on cylinder.
Base gasket can be the clearance adding 0.5mm more.

Later cylinders using special knock pins and thick o-rings for oul returns. Make sure they are not too tall. Easy to file off some.

The sleeve flanges must be very thin when milled that much.
The cylinder height is interesting. Must be lower than 84 mm.

Cruzinimage pistons do not cost much.
My K2 got their K7/8/F1.... (392) +0.50mm pistons with a little more dome. Total clearance piston-bore  dia must be tight. I think mine got ca 0.02mm. Piston skirt dia measured 12 mm from bottom.

My cheap compression tester showed 170-180 PSI.
Earlier another cylinder  with CI stock pistons, 150-160 PSI.
Same cam, K7/K8 cam.

That engine takes almost no oil at all. Last oil change after 5500km. Maybe around 5mm lower on dipstick. Probably the minor case weep.

I visited a bike collector 90km away from me last year. Mostly CB750. The house
He used the CI 836 pistons in most his CB750 restores. Extra torque is a good thing

[lash]

Mark, I will think about that and maybe take you up on it. Shoot me an email on cost.