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Discussion Starter · #1 ·
Hi All,

Symptoms
General rough running especially at idle
Intermittent white/grey smoke blowing from the right-hand pipe.
Oil smells like fuel

I completed a cold compression test with the following results.
I tested each side 3 times then added some oil to the combustion chamber and retested 3 times
Spec Minimum Target = 170psi
Test:
Right Hand Side = 125psi
Left Hand Side = 145psi
Oil Added
Right Hand Side = 220psi
Left Hand Side = 210psi

These results indicate a problem with the pistons, piston rings &or chamber wear.....? I'm planning on going to remove the head to assess both.

The questions:
Should I remove the engine to complete these repairs? or is it more practical/possible to keep the engine mounted?
Do you have any experience with aftermarket pistons & rings vs OEM?

any head rebuild advice is appreciated:I am mrgreen::mrgreen:


Thanks, Heaps !
 

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FIRST THING TO DO IS CHANGE THE OIL. Oil contaminated with fuel can trash the the engine in short order. Be sure to close the petcock every time you shut the bike off.

Cold compression readings are pretty much irrelevant. Repeat the compression test with the engine at operating temperature and the throttle and choke wide open.

Low compression contributes to loss of power but your symptoms are more likely the result of ignition or carburetor issues. Start with a basic tuneup. If that doesn't fix it you might proceed to a carb re-build.
 

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Too much oil added results in too high of compression reading. No more than 5 cc's should be added. But even with the readings you minimally have rings to do, possibly valves as well but until they're inspected you won't know. Valves on these engine cannot be ground, replacement only.
+1 on getting the fuel diluted oil out of there ASAP.
The top end can be done with engine in frame, lots of kneeling and bending involved since it's so low to the ground. Myself, I'd drop the engine and get it up on a bench. I'd suggest OEM rings vs. eBay stuff.
 

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Get the manual from here and look at cmsnl for the exploded views, which can only help.

I hope the centre head bolts are not problematic for you and you have the flywheel and clutch tool.
 

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Discussion Starter · #5 ·
@JT , Thanks, I have been careful with the petcock valve as this is the second time I have replaced the oil recently due to the fuel smell.
I have removed carbs cleaned, checked and serviced. I do have fouled spark plugs at a leaned out state on carbs.
I have not check ignition timing at this stage.
I will complete a warm compression test and compare results
Question: shouldn't the float valve stop the flow of fuel and the float bowl overflow would drip if flooding is occurring?

@LDR, Thanks, I did wonder at the compression values being so high on the second test.
OEM rings, hopefully, rings are all I need.

@drydreamer, thanks, I'm confused why do I need the flywheel and clutch tool?

At this stage, I feel all roads lead to head removal.
 

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In a perfect world the float valve and the standpipes would protect the engine from overflowing fuel. Not necessarily so in our world.

Please expand on your comment about fouled plugs and lean condition. A lean condition may indicate vacuum leaks or there may still be carb issues. You may want to review this just to make sure you got the rebuild done right. Not many do on the first try.

http://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html

There is no adjustment for the ignition timing though it is possible for the key that holds the flywheel to shear. Not real common.

No need to remove the flywheel or sidecovers to rebuild the top end. You likely will want to remove the left side cover so you can use the flywheel bolt to hold the crankshaft in position for assembly.
 

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Discussion Starter · #7 ·
I'm picking up what you're putting down JT.
My Lean condition: from the spec 2 turns out. I screwed the mixture screws in as far as I felt comfortable hoping to reduce the black oil/fuel deposited on the spark plugs.
I had some success on the left plug but the right side continued to get "fouled" black. I introduced other issues by winding in those screws like backfiring.

I'm not saying I did a top job cleaning the carbs however I did a fair bit a research, purchased Larrys Guide to rebuilding Keihin Carbs. I didn't go the full Ultrasonic
cleaner but I stripped those things down to bare bones and gave it a good clean, replaced a few o rings, blew out and cleaned all the nooks and crannies.
made sure it was all stock as far as jets go. The only thing I was reluctant to do was to pull the low jet emulsifying tube as it looks like a good way the damage carbs.

I've given those carbs a good chance to fix this issue. I'm going to open it up, take a look at pistons/rings/valves and go from there.
Thanks
 

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@drydreamer, thanks, I'm confused why do I need the flywheel and clutch tool?

Give it time dear friend, give it time.

Also get a 10mm x 1.25 tap to make sure the head bolt holes in the upper crank case, the 4 centre ones mainly, are in good shape and clean all the way down to the bottom.

Any signs of an oil leak/sealer around the 4 centre head bolt holes ?
 

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The mixture screws adjust the mixture at idle. They have little effect at throttle settings much above idle. The "specified setting" is only a starting point from which each carb is adjusted to achieve the highest idle speed. The carbs also need to be synchronized.

Any results from your repeat compression test?
 

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Discussion Starter · #11 ·
@ Daydreamer , I get it, a bottom end rebuild is inevitable, is it? I'll try to get by without it for now. I didn't notice any sealer around the centre bolts. I will have a closer inspection

@JT, Roger on the mixture screws. I didn't know what else to do to reduce the plug "fouling." besides rejetting to a smaller size (below stock)
I bench synced carbs. I will take the bike to a shop with gauges for an accurate sync.

Repeated Test Warm
Compression Test CB400T.jpg

@LDR yeah he was having a little inside joke but he may have a point.
 

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@ Daydreamer , I get it, a bottom end rebuild is inevitable, is it? I'll try to get by without it for now. I didn't notice any sealer around the centre bolts. I will have a closer inspection.

Its drydreamer, but you are forgiven as you green and upside down.

You have an experience coming which I hope will be a good one. Take your time and enjoy.

If you are taking the head off, get the tap mentioned, and whilst the head is off, rinse out the sump and kick start oil trough. The clutch basket "fingers" also trap crap a bit like a centrifugal oil filter, but can be cleaned without taking the clutch off the engine. How is the clutch slotted nut ? mangled, or ok and tight ?

Don't be tempted to use the oil filter bolt to extract the flywheel. Make some measurements and see why. Take the oil filter bolt ( or measure thread and pitch ) to your fastener supplier or MERC workshop to get a bolt for flywheel extraction.

If you cannot get a bolt or ready made ( don't use a 3 leg thing ) extractor, and have access to a lathe, then the oil filter bolt can be safely adapted for flywheel removal, by having a larger hex drive, and steel "button" . Be very carefully with those delicate and easily murdered stator windings.

If adapting the oil filter bolt, get a new replacement.
 

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Discussion Starter · #13 ·
Ah Yes, Drydreamer it is. I blame spell-check.

Head is off.

I checked valves for leaks by pouring fluid into the IN/EX ports. No leaks were evident so I will leave the valves alone for now.
Plan:
Purchase step up OS pistons & rings.
Take the head to the machine shop with new pistons for a rebore and hone.
Get the valves vacuum tested for leaks.
Put it all back together and go for a ride ... hopefully.
I'll take your advice on the tap, however, I won't be needing the fancy oil filter bolt/flywheel remover at this stage unless I start having issues with the bottom end.

Is it advisable to rinse out the sump with a more lucid liquid to clean it ? or possibly warm the oil before running it through?

Thanks for the advice
 

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The design of the lower case makes it difficult to get really clean w/o splitting. I'd think about using a solvent and shaking the engine around as much as possible to flush out what you can
201_4197.JPG
 

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If the engine is still in the frame, then its relatively easy to flush out the sump and labarinth, as well as the kick start oil trough, if the clutch cover is off. If the clutch cover is off then its insides and clutch basket can be cleaned/flushed.

Don't use a high pressure cleaning lance as this tends to "splatter" the debris everywhere. Use a safe solvent in a clean and empty washing up liquid squeezy bottle, or hand pump/low pressure affair, similar to a hand operated ( or 12v, sparks so a fire risk maybe ) model aircraft fueling pump and tubing etc.. Asses via the gap/gaps between the crank ladder casting and crankcase, gaps in transmission/g/box area, and a bent pipe to access/empty/flush the kick start oil trough.

Since the head is off and possibly the cylinder barrels also, then there are large "holes" for access.

The left picture above shows the somewhat still dirty sump along with the kick start oil trough.

Once the majority of the debris has been flushed out, then a higher pressure cleaning lance will go a good job of removing most of the other dirt without so much "splatter".

A good solvent will remove most if not all of the "dirt", just give it time to work.

It will not take long to clean out the sump etc., so is well worth doing.

Make sure no debris is stuck to the hooded oil pick up pipe filter screen, which will be visible via the sump plug hole. It is possible to "reverse flush" the oil pick up pipe filter screen, to some extent.
 

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Discussion Starter · #16 ·
OK Great, Appreciate the advice.

I'm holding off on splitting the crankcase as I feel I have gone as far as I feel comfortable going at the moment
file-2.jpg
I will take the clutch cover off and give the basket a clean.
On inspection, through the "holes" it looks pretty clean down there.. at least what I can see.
I did, however, notice a few things.

1. Cam chain tensioner guide looks brittle and there are cracks showing. also, a small piece is missing CamChainGuide.jpg

2. Wear from the cam chain is present on the cylinder barrel walls WallDamage.jpg WallDamage-2 (003).jpg

I'm guessing a replacement guide is needed?
Is the chain getting loose and causing the damage in the barrels? can't be good.

I'm waiting for my next paycheck to order parts. I have been eyeing up these
https://www.ebay.com.au/itm/322580070423
 

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Discussion Starter · #18 ·
Does the chain wear indicate a definite stretched chain? or could this be a result of the chain tensioner not being applied in the past?
in other words...
Is there another method of verifying that the cam chain needs to be replaced?

Thanks for the link.
 

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Most likely lack of maintenance. The check is after it's been adjusted to try to lift the chain at the top of the cam gear, if you can see the top of a tooth then the chain is stretched.
 
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