rebuild 6 month review + a mystery - Honda Motorcycles - FireBlades.org
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post #1 of 18 Old 12-29-2019, 1:55 PM Thread Starter
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rebuild 6 month review + a mystery

Hi all,

first, a bit early but a haapy new year to everyone, hopefully lots of dry warm days this year.

So... rebuilt my 929 in april, rebore and honed to +1mm, making it a 954 now. Had some issues with oil consumption at first, and it seemed to improve somewhat but still consumed more than it had before.
Fitted JE pistons, 12.5:1 instead of the standard 11.3:1.
Stripped the engine down a few days ago, I've probably done 5000 miles since the rebuild.
First thing that struck me was the oily deposit on the pistons and combustion chambers. See pic, left hand piston. right is standard from pre-rebuild. this is a soft deposit that you can remove with your fingernail. Looks like 2-stroke gunk.
First thing I checked was that all the piston rings are fitted right way up. They are, and all gaps are good. The mapping is set up is set for about 16:1 air/fuel on light load, dropping to 12.5:1 on full throttle. (Got a lambda sensor fitted). Exhaust valve stems are white, just as previously. Spark plugs are clean, very light milk coffee colour.
there is some scuffing on the front and rear faces of the cylinders, no more than usual, no deep scratches.
Hone marks are still very evident, despite me giving it a fairly hard run-in during the first 30 miles, and did not over-baby it during the following few hundred miles.
Compression pressures are good, all up in the 200-210 psi range.

So the question is...anyone else have high oil consumption with JE pistons? I note that the 6 oil drain holes from the oil control ring grooves through to the inside of the piston are completely differently arranged - they are distributed round the full circumference of the JE pistons, whereas the standard Honda piston has 3 front and 3 back, in the centre section of the piston. Want to get a few more facts before I start drilling more drain holes....
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post #2 of 18 Old 12-29-2019, 2:10 PM
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Re: rebuild 6 month review + a mystery

I have never seen such a difference in piston crowns unless there is a valve stem seal problem which you say you've ruled out. Saying that, the 'pre-build' piston looks as if it's been running rich.

So, are you saying the whole four piston crowns are equally oily?

Have you taken into account how the engine was running immediately before disassembly? I'm sure with your experience you'd know that if the bike had been left idling for some time, there would be unspent/unburnt fuel in the chambers that would not burn off any oil deposits. However, even in saying that, I still believe there is blow-by through the valve stem seals.
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post #3 of 18 Old 12-29-2019, 5:14 PM Thread Starter
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Re: rebuild 6 month review + a mystery

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Originally Posted by nigelrb View Post
I have never seen such a difference in piston crowns unless there is a valve stem seal problem which you say you've ruled out. Saying that, the 'pre-build' piston looks as if it's been running rich.

So, are you saying the whole four piston crowns are equally oily?

Have you taken into account how the engine was running immediately before disassembly? I'm sure with your experience you'd know that if the bike had been left idling for some time, there would be unspent/unburnt fuel in the chambers that would not burn off any oil deposits. However, even in saying that, I still believe there is blow-by through the valve stem seals.
Nigel, the valve seals were all replaced at the rebuild. All 4 piston crowns were equally oily. You're right, the pre-rebuild piston shows that I tend towards a rich mixture, or maybe just don't stretch its legs enough. But it's dry, totally different to the black slime that coats everything now.
I was thinking about it since posting, and I guess the oil film pressure between the piston and the cylinder is higher in the front/back of the cylinder than the sides, where the piston is applying more thrust. so it stands to reason that drain holes placed in that zone would pass more oil than those placed elsewhere. which is probably why Honda decided to place the drainage holes in that zone. I doubt that JE would agree with me on this, that would be admission of incompetence. But I'm seeing in various forums that JE pistons or in fact any aftermarket forged pistons (e.g. Wiseco) often provoke oil consumption problems.
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post #4 of 18 Old 12-29-2019, 7:43 PM Thread Starter
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Re: rebuild 6 month review + a mystery

reading around the subject confirms what thought. This is typical: https://z22se.co.uk/threads/the-reas...olution.29284/

So the trick is to allow enough oil to drain away, but not too much. It may be that JE saw that the standard pistons drained too much oil from the area where scuffing normally takes place between the piston flank and the cylinder wall, see my pictures above. And they maybe tried to remedy the situation by moving the drain holes away from that zone. But not only have they overdone it, they haven't fixed the problem, although I have to say that the scuffing I see on the rebuilt engine is dramatically less than I've seen on standard 929's, which are ALWAYS scuffed, but seem not to suffer much ill-effects as a result.
So they haven't completely fixed the scuffing, and instead have caused another problem, insufficient oil drainaway. I just don't like the buildup of this gunk, so I'm going to drill holes in the JE pistons to match the geometry of the Honda pistons. I doubt whether talking to JE will yield any sense, they can't say anything in case they get sued.
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post #5 of 18 Old 12-30-2019, 5:07 AM
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Re: rebuild 6 month review + a mystery

Most fascinating, OB.

Firstly that you would choose to insect your motor after a rebuild, and secondly that there now appears a resolution as acknowledged in the link you provided.

I'm guessing you have some good workshop/garage equipment as I can't see a piston wedged between knees with an electric drill hovering above being a very precise operation!

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post #6 of 18 Old 12-30-2019, 12:08 PM Thread Starter
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Kinda precise....fiddly anyway. JE holes were 1.1mm, bored them to 1.3 and of course added the one in the middle. We shall see.
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post #7 of 18 Old 12-30-2019, 2:03 PM
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Re: rebuild 6 month review + a mystery

Looks magic. All the boys'll be sending you their pistons now!!

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post #8 of 18 Old 12-30-2019, 2:28 PM
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Re: rebuild 6 month review + a mystery

Quote:
Originally Posted by oldbastard View Post
Kinda precise....fiddly anyway. JE holes were 1.1mm, bored them to 1.3 and of course added the one in the middle. We shall see.
Wow, I remember back in the day that the 929 and 954 had extremely short piston skirts. But that JE is even smaller. Also, no coating on the skirts?

I truly admire you #1 doing the rebuild and #2 tearing it down again to see whatís happening in there.

Do you think you need weigh the pistons after the mod? Iím a rookie engine builder and once suggested to a member to weigh and balance a new piston being installed among 3 t hat werenít. I was shocked when Bladeracer said it wasnít necessary.

I do love how you made your own decision to add the holes. F it, good for you. But youíll have to take it apart again to see if it made any change

Canít wait until next winter to see what (if any) the result is.
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post #9 of 18 Old 12-30-2019, 2:59 PM Thread Starter
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Re: rebuild 6 month review + a mystery

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Do you think you need weigh the pistons after the mod? Iím a rookie engine builder and once suggested to a member to weigh and balance a new piston being installed among 3 t hat werenít. I was shocked when Bladeracer said it wasnít necessary.

I do love how you made your own decision to add the holes. F it, good for you. But youíll have to take it apart again to see if it made any change

Canít wait until next winter to see what (if any) the result is.
Ian, the same mod was done to all 4 pistons, and they were all within half a gram of each other.
As for results, hopefully that will become clear as soon as I get it back together and see what the oil consumption is. I could always stick an endoscope down the spark plug holes, that black gunk is easily recogniseable......
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post #10 of 18 Old 12-31-2019, 11:57 AM
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Re: rebuild 6 month review + a mystery

Quote:
Originally Posted by oldbastard View Post
Ian, the same mod was done to all 4 pistons, and they were all within half a gram of each other.
As for results, hopefully that will become clear as soon as I get it back together and see what the oil consumption is. I could always stick an endoscope down the spark plug holes, that black gunk is easily recogniseable......
Right on then, I hope you get the result you're after. I know you will update us on the status.

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post #11 of 18 Old 01-01-2020, 11:42 AM
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Re: rebuild 6 month review + a mystery

Oldbastard, WOW...Take motor out, rebuild, Put back in,
something still not right, take back out and take back apart
to see whats wrong, drill holes, put back together.
That is some serious wrenching time.

.
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post #12 of 18 Old 01-02-2020, 1:07 PM
 
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Re: rebuild 6 month review + a mystery

Good work, it seems you will be soon referred, piston consultant.
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post #13 of 18 Old 01-02-2020, 2:19 PM Thread Starter
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Re: rebuild 6 month review + a mystery

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Good work, it seems you will be soon referred, piston consultant.
Better than piston broke, I guess. (Sorry, old british humour)
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post #14 of 18 Old 01-02-2020, 3:50 PM
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Re: rebuild 6 month review + a mystery

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Better than piston broke, I guess. (Sorry, old british humour)
Gotta help you out here, OB.

We both know that British humour is at the top of the tree, whereas our American friends struggle to understand any humour that is not related to politics, race, and the daily events of Caitlin Jenner.

So, here it is: piston broke is to be read as 'pissed and broke'.
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post #15 of 18 Old 01-08-2020, 5:17 PM Thread Starter
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Re: rebuild 6 month review + a mystery

got the engine all back together, the cylinder head was from an engine I bought as scrap, and everything went together really nice. the last thing was to put the spark plugs in before getting the engine off the bench. that's when I discovered one of the plug holes has stripped threads. I've been through the search engine to find plug thread specs, but no success, no-one seems to quote them. Can anyone enlighten me? I can feel that old familiar Helicoil anxiousness welling up...I could just fit the old head and save the (ridiculous) cost of a head gasket ...but...

some folks report doing the job with the head still mounted, and I can see that it could work, given enough grease on the cutting tools, but part of me wants to get the head off and do it "properly". Anyone else done the in-situ repair without problems? Any tips?
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