SOHC.co.uk Forums > CB350/400

Engine rebuild - bore glazing

(1/2) > >>

Mr-Gear:
Hi All,

I have a rebuilt CB400F engine where the bores have been machined oversize to 51.25mm paired with 0.25mm oversize pistons/rings (pattern from DSS).

During assembly, ring gaps and piston OD was measured within spec.

Break-in procedure followed as per the Honda shop manual guidance using mineral engine oil, local riding working through the gears at various RPM ranges.

Since the rebuild and subsequent break in, the engine appears to be performing well and compression values are ~150psi evenly across all cylinders after what is now 2000 miles. There have been a few occasions where the engine has been held at at a constant speed on the motorway as I like to travel on the bike (I'd estimate 6-7K RPM for an hour or so).

Out of curiosity, I popped an inspection camera into the bores and saw that cylinder 1 has polished areas (perpendicular to crankshaft) at the bottom portion of the cylinder wall. (see attached picture). This feature appears across all 4 cylinders in the same places to the same extent.

Being magnified by the inspection camera could just be making it look worse than it is. I have not disassembled the engine to investigate further at this stage, as it is all nicely finished with Cerakote and I wouldn't want to risk damaging the finish unnecessarily.

Question:
Is this normal or expected?
If not what could be some suspected causes?
Is this detrimental to the engine?

Thank you.

Bryanj:
The "honing" looks a bit rough to me and the smooth bit would be the rings making it smoother

McCabe-Thiele (Ted):
Curiosity killed the Cat.

Fitting an oil pressure gauge makes you worry about oil pressure, as long as the oil light goes out when you start the engine that all Mr Honda deemed necessary.

Putting an Inspection Camera down you bores is verging on the paranoid.
Was there a solid reason you even looked, oil consumption or something?

It's probably oil marking from the oil thrown up  by the crankshaft journals.
The pistons are travelling at a fair speed when going down on the firing stroke, then changing direction at BDC on the return for exhaust, repeat for induction & compression. Pistons distort under such loads at high rpm, the fact that it's on all four sounds good to me. As Bryan has said it could be just the bores bedding in, check it again at 10,000 miles, it might be the same  all over.

My mobile is great at making things look bent or out of shape, especially on close ups.

TrickyMicky:
If the shiny portion(s) are towards the front and rear of the cylinders, then this is quite normal.  On the firing/downward stroke, as the crank turns the con-rod is not in a vertical plane, and it gives the piston a 'slanting' tendency thereby exerting more pressure at these points. If ever you get the chance to look at a large  marine diesel, or a steam locomotive engine you will se that the connecting rod from the base of the piston operates a crosshead, which keeps the piston square in the bore. I would put your camera away, and if it's not using oil, stop worrying and enjoy riding.

Mikep328:

I'm on a Norton Commando website regularly where quite a few people have installed oil pressure gauges and now spend a lot of time worrying/commenting about oil pressure.  There is NO history of Commandos failing due to lack of oil pressure.  But with a gauge it can now be observed and, therefore, worried about!

If the engine is running well, not using oil, no smoke, etc, no need to worry about things just because you can!!!  ;)

Navigation

[0] Message Index

[#] Next page