Topic: How can I restore compression...

[iya0yas]

...assuming the valves are adjusted properly.  I am taking a break from my '76 400F to work on a '72 CL175 K6 that has not run in 25+ years and has 5,300 orig. miles.  I recently had the top end apart to remove a broken spark plug (right cyl.).  I noticed the piston rings were 'gummed-up" and 'bonded' in their grooves with old oil.  I cleaned the pistons and wire brushed the rings to the extent that I was happy with the result.  I did replace the base, head and cam cover gaskets and used Yama Bond #5.  Carburetors were also carefully cleaned with OEM jets & seals installed and floats set to 21mm per spec.

Fast forwarding with the bike completely reassembled...I attempted to start the engine.  The engine would start with the throttle slightly open but only fired on the left cylinder and no more than 500RPM (Even at full choke the engine would not start).  The right cylinder felt slightly warm but probably due to heat transfer from the left cyl.  Spark from both coils was very good. 

Due to the hard/no starting I thought of those rings and decided check compression (something I should have done before installing the engine) whereby I removed both plugs, held wot & several kicks with the kick start lever.

The results were poor:
Dry: 
Left Cyl.: 110psi
Right Cyl.: 50psi

Wet w/10W-40 oil:
Left Cyl.: 150psi
Right Cyl.: 90psi

Notes:
- Left & Right orientation as perceived by the rider when sitting on the bike
- Compression spec. for this bike ranges between 134 & 238psi.  (with no more than a delta of 25% between each cylinder)

I am encouraged to see that the wet compression values improved slightly.  I have ordered a set of new rings and c-clips for each piston and am prepared to "do the right thing" this time and install these components like I should have done when the engine was apart the 1st time   

However in the mean time I am periodically spraying PB blaster in the spark plug holes as well as gently cycling the pistons with the kick start lever.  I hope this will eventually restore enough compression in the right cyl. so that I can start the bike and let the engine warm up enough to 'free' the rings.  (Yes, I plan to change the oil in short order after I resolve the compression issue)

So...besides soaking with PB Blaster, are there any other thoughts/comments from the forum on how to restore compression without going through the effort and time of pulling the engine and ancillary components?

Thanks-

[cgswss]

First- I'm sure you know this... make sure you do a low speed hone so you can get a nice cross hatch on the inside of the cylinders.  I would use nothing but a 3 stone hone-and I would never use a flex hone.

THe compression numbers you show should allow the engine to run under no load right up the RPM range.  I have a feeling you have some other problem.  I would review your cam timing procedure.  Are you sure you were on the compression stroke?

In the end, I wouldn't worry about it too much until you get the new rings and do a nice hone job.

[iya0yas]

Thanks for the tip on the 3-stone hone.  Any recommendation for where I can buy such a hone? 

You also mentioned cam timing on the compression stroke.  Are you referring to setting valve clearance (0.002" ex. & in.)?  If so then yes, I made sure clearance was set on the compression stroke whereby the "T" mark on the alternator rotor was aligned with the index pointer.  I rotated the rotor 180deg. and repeated this alignment process to set valve clearance for the 'other' cylinder. 

If you are referring to something other than valve clearance then please elaborate...I'm still learning and do appreciate the information.

[killersoundz]

If you think the rings are frozen onto the pistons (which happens if the engine sits for a long time) then don't run it! You might scar up the cylinder walls. One cylinder in my barn fresh cb750 has frozen piston rings that rusted to the piston, they were partially the reason the engine was locked up.

In order for the new piston rings to seat well and give you good compression you must hone the cylinder walls. Get a nice 30 degree criss cross hatch pattern on there with the hone tool on a drill at very LOW SPEED, up and down.

I have this hone, works fine.

http://www.amazon.com/Tools-KDS2833-Engine-Cylinder-Hone/dp/B0002SREPE/ref=tag_dpp_lp_edpp_img_in

My advice is to get the bike back together after you install the new rings and hone, then fire it up, let it warm up a little and take it for a nice cruise immediately. Get on it, but not so much to cause overheating. This allows the new rings to bite or 'seat' into the cylinder walls before it smooths them out, which is how you get better compression.

[phil71]

you reused rings that were stuck in ringlands? You don't deserve compression

[phil71]

seriously though, don't do that.

[dave500]

Compression spec. for this bike ranges between 134 & 238psi.  (with no more than a delta of 25% between each cylinder)

is it a diesel?

[lucky]

Compression spec. for this bike ranges between 134 & 238psi.  (with no more than a delta of 25% between each cylinder)

is it a diesel?

Even a VW diesel rabbit has 600 lbs. of compression.

[dave500]

we dont like rabbits here we shoot them.

[iya0yas]

Thanks for the info. & hyperlink killersoundz...

Yup, those are the compression numbers indicated in my Clymer manual #M321 (Honda 125-200cc Twins '65-'78).  Perhaps the Clymer manual differs from the Honda manual...? 

[wrenchmuch]

What condition are your valves in ? The wet numbers came up the same amount on both cylinders. Although the numbers indicate poor ring sealing in both cylinders , the fact that the low cylinder didn't come up more in relation to the high cylinder points more towards poor valve sealing. A valve could be stuck open or just not seating properly anymore. 


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[Music City Metalcraft]

Assuming the valves are OK is never OK. Measure.
Using a hone in the cylinders will only make everything worse. Apart from slightly enlarging the diameter, you also force the worn rings to bed in again, wearing them more.
What was the ring gap in the bore? Obviously too big, by the numbers.
Anyway, it looks like the jugs have to come off again... no magic potion here.

[Bodi]

Actual compression psi specs are not a useful target. The engine displacement is so small (102cc/cyl) that the compression tester design makes a huge difference in the reading: yours and mine will give different but equally valid psi readings. We don't know what tester Haynes or Honda used, our measurements can only be compared to theirs if we used the identical model.
You are looking for reasonable compression and a good balance between cylinders. You do not have this balance.
It could be valve or ring/cylinder trouble.
Listening at the intake and exhaust ports while slowly turning the engine over, you will hear the hiss under compression if a valve is leaking.
If the valves sound good, and you can look in the spark hole and see a clean bore, I would recommend opening the top end and checking whether a ring is stuck or broken. Inspect and measure the bores, if they're circular and sized within specs a rebore is not necessary. New rings are pretty much required but you can re-use good used low-mileage rings if the end gaps are OK. Not a good plan but possible. A light crosshatch hone to aid reseating the rings is required as with new rings.
How many miles? The valve guides are suspect on high mileage 350/400 engines, new guides gets into quite a few dollars. For low mileage engines just lapping the valves and checking the sealing ring is enough. You should not recut the seats unless you really have to, this reduces compression as the valve sits deeper (remember the tiny displacement) and replacing the seats is not cheap. Regrinding valves is not recommended because of the thin Stellite coating, new valves are a bit pricey too.

[cgswss]

Before we have you rebuilding everything on the bike...  You have to pull the bike down when you do the rings.  Simply set the head upside down  as level as possible and fill the compression chamber with gas.  If the gas leaks out quickly, you know you have a valve problem.

Do you have a "sand" blaster?  If you do, blast the plugs (then blow them out with compressed air)  With all the crap you are spraying in the bores, I'd bet you have fouled plugs, and there is no sense in putting in new one until you burn the crap off.

[iya0yas]

Excellent advice from all...  The most obvious thing that comes to mind is that I did not pay attention to the ring orientation when I assembled the cylinder.  It's very likely they are not set 120deg. apart.  I also did not remove the rings, place one in its respective cylinder and measure ring gap nor did I measure the bore dia. for each cyl.  The odometer indicates 5,300 miles which I believe to be original.  I'm the 2nd owner and per my discussion with the PO I assume for now this engine has retained its std. bore.

My plan is as follows:

- Remove the engine from the chassis
- Measure/document valve clearance for reference
- Disassemble the top end again
- Visually inspect each cylinder bore for obvious wear, scoring, etc.
- Measure/document each cylinder bore dia. top, middle & bottom (Anyone know the spec. +/- tol.?)
- Remove the old piston rings and for ref. install one ring in its respective cyl. and measure/document the ring gap (Anyone know the spec. +/- tol.?)
- Visually inspect each piston for obvious wear, scoring, etc.
- Measure/document each piston dia. (3-plcs.)  (Anyone know the spec. +/- tol.?)
- Assuming the pistons and cyl. bores are within spec. I will lightly hone the cylinders as instructed with a 3-stone hone
- Install one new ring in each cyl. and measure/document ring gap
- Install new rings on pistons (noting the oil sealing rings and their sequence of assy.)
- Carefully orient the rings so they're 120deg. apart from one another (is there a datum/recommended point for alignment of the top or bottom rings?)
- Measure/document the radial free play of the con rod (Anyone know the spec. +/- tol.?)
- Install pistons and measure/document the radial free play of the wrist pin bearing/piston assy. (Anyone know the spec. +/- tol.?)
- With the head assy. removed I'll invert it and perform a leak down test with acetone.  If necessary I'll lap the valves and repeat the test
- Reassemble the engine using more Yama Bond #5 on all gasket mating surfaces
- Measure/document & if necessary adjust valve clearances
- Verify carb slides are synchronized wrt throttle position
- Install engine into chassis and perform another compression test (semi-wet I suppose with WD-40 lube on rings during cylinder reassembly)
- If compression is "good" I'll drink a beer and finish the rest of the vehicle assy.
- Install new spark plugs and fire her up...
- If compression is "bad" I'll drink 6 beers and start over...the next day
- Other...Did I miss anything along the way...?

Again, many thanks everyone for taking time to reply to my post...


Dear cgswss, you stated "I would review your cam timing procedure.  Are you sure you were on the compression stroke?" Is this the same as checking/setting the valve clearance?

 

[Music City Metalcraft]

Sounds like a plan. especially the beer 

[cgswss]

Yes- two separate things-  Making sure you have the cam aligned correctly before installing the timing chain.  (I don't know the procedure on your bike but on many of the ohc engines you have to rotate the cam 180* to install one of the nuts and when you bring it back you have to make sure the mark on the cam lines up with its index and the crank is lined up on its index.  There is slack in your cam chain so you must rotate the crank CLOCKWISE to keep the slack out.

Valve setting must be done at TDC on the compression stroke.

Don't forget to invert your head and fill the chambers with gas to check for leak down.

Also- I'm sure you know, the two top rings are NOT the same.  The top ring should be square.  The second ring should have a taper to the outside.  Tha is the bottom of the ring is a little bigger around then the top.  It is most important to make sure you have those rings in the right slots and the 2nd ring tapered side up.

When you measure you ring gap it is very important that the ring be square in the bore,  I put in it the use the top of the piston to push it down a little before measuring.  I use an end gap on the compression rings at .004"  I know some that take it out as much as .012"  The oil ring I set at .012.  I consider a compression ring as "worn out" if the end gap exceeds .025,  Oil rings can go 040"

I would not worry a lot about taper in the bore or piston.  Your going to hone the bore and I'm sure its not worth the time or money to replace the pistons.

I would get a piece of glass and lay it on the top of the cylinders to check for flat- then do the same thing by laying the glass on top of the cylinder head.  If you can get a .010 filler gauge in there- you need to have the head milled.

hope I haven't further confused you

Craig

[Bailgang]

I can't help but wonder if you have something else going on as well because my 71 cb175 initially had 1 cyl that only had 90 psi and it actually ran fine. I did re-ring it which got both cyls up to 135 and course made it run even better but that 1 cyl that initially only had 90 psi didn't keep that cyl from firing.

[iya0yas]

Okay, been waiting on parts so I removed the engine and disassembled the top end.  In the process of doing one last compression test (wet) I discovered the main reason for such low compression in the right cylinder.  During an attempt to remove what remained of the spark plug threads from the head I used a center punch applied to the broken edge of the plug threads in an attempt to 'unscrew' them from the head.  During this process I inadvertently made a depression in the head adjacent to the OD of the spark plug threads (see pic.).  The depth of this deformation is deeper then the first two threads of the helicoil so I am getting blow-by during the compression stroke (see short video).  I ended up using a product called Seal-Lock Fluid Weld (http://www.amazon.com/Seal-Lock-Fluid-Weld-2-oz-Bottle/dp/B002YJG8GU) good up to temperatures of 3000F.  I heated the head and applied this sealant to both exposed faces of the helicoil.  Let's hope this does the trick...

Here's some pic's for your viewing pleasure...there's more to come.

CL-175 K6 As received


After a little tlc


Fuel tank and gas cap before vinegar & water (50/50)...not good



Fuel tank and gas cap after degrease followed by vinegar & water



Center punch deformation...looks innocent enough huh?



Short Video of leak:
1972 Honda CL-175 K6.MOV

Cylinder bore (typ.), awaiting the flex hone



Cylinder bore after hone


Left Cyl. Piston w/o rings




New Piston rings


The larger 2nd ring from the top is larger in surface area than the stock ring


Top ring


Middle ring


Bottom ring set: (3pc.) 



Cam Shaft & Rocker assy. - Note the "D" stamping to indicate TDC



Cyl. Head - Clean gasket surface








   

[dave500]

looking good,make a ring groove scraper from an old ring,get those ring grooves clean without gouging them,use what ever drill bit fits through those oil holes on the piston and make sure they are well clean,use fine steel wool and clean the ring lands of any build up and try and polish those slight scores from the skirt with it aswell,youll be using new wrist pin clips off course.