Topic: Weird Compression - Oh, Maaaaaan...!

[Tracksnblades1]

TnB: when I was trying to get the cylinder head to seat, I apparently overlooked one of the thin 'sandwich' parts of the oil ring which must have =been proud of the ring land; the weight of the head bent it Over the edge of the ring land.

HM: I'm still in the process of putting it together; I'm having a bit of a time getting the cam chain back onto the sprocket. I have the adjuster turned all the way to the right and locked down with the nut - but how can I get some more slack?

Do you know the difference between a cylinder head and a cylinder block..?

What’s the piston to cylinder wall clearance that will allow an oil ring rail to bend over the ring land..?
😳

[Dr. Frankenstein]

Yup, I sure do; I just call the whole thing 'the head' - apparently it seems to drive people nuts. Maybe I need to spell it out a little bit...

"What’s the piston to cylinder wall clearance that will allow an oil ring rail to bend over the ring land..?"  Well, whenever you set the (ahem) CYLINDER BLOCK down over the pistons in preparation to place the CYLINDER HEAD on top of the CYLINDER BLOCK, sometimes those ultra-thin oil rings that SANDWICH the crenellated middle oil ring don't cooperate and will stick out a little from their ring-lands...and if you don't SEE it and don't push them back IN, the weight of the CYLINDER BLOCK sliding down over the piston can catch the rim of that ultra-thin oil ring and bend it parallel to the piston skirt; so when the CYLINDER BLOCK seems to 'stick' for no reason, you pull the CYLINDER BLOCK back off to see why it won't go any further and find a bent oil ring.

...better...?

[grcamna2]

Yup, I sure do; I just call the whole thing 'the head' - apparently it seems to drive people nuts. Maybe I need to spell it out a little bit...

"What’s the piston to cylinder wall clearance that will allow an oil ring rail to bend over the ring land..?"  Well, whenever you set the (ahem) CYLINDER BLOCK down over the pistons in preparation to place the CYLINDER HEAD on top of the CYLINDER BLOCK, sometimes those ultra-thin oil rings that SANDWICH the crenellated middle oil ring don't cooperate and will stick out a little from their ring-lands...and if you don't SEE it and don't push them back IN, the weight of the CYLINDER BLOCK sliding down over the piston can catch the rim of that ultra-thin oil ring and bend it parallel to the piston skirt; so when the CYLINDER BLOCK seems to 'stick' for no reason, you pull the CYLINDER BLOCK back off to see why it won't go any further and find a bent oil ring.

...better...?

Better

[Dr. Frankenstein]

Awesome! 

[Ozzybud]

There is nothing wrong with a compression reading  of 95-102.
The point is that the be within 5-10% of each other.
What's the volume of your tester? If  there is a long hose with higher volume it will make the reading lower.
Also you have new rings that are not broke In and sealing yet.
I am assuming you have the proper cross hatch on the cylinder walls for the type of rings you are using.

[Tracksnblades1]

Yup, I sure do; I just call the whole thing 'the head' - apparently it seems to drive people nuts. Maybe I need to spell it out a little bit...

"What’s the piston to cylinder wall clearance that will allow an oil ring rail to bend over the ring land..?"  Well, whenever you set the (ahem) CYLINDER BLOCK down over the pistons in preparation to place the CYLINDER HEAD on top of the CYLINDER BLOCK, sometimes those ultra-thin oil rings that SANDWICH the crenellated middle oil ring don't cooperate and will stick out a little from their ring-lands...and if you don't SEE it and don't push them back IN, the weight of the CYLINDER BLOCK sliding down over the piston can catch the rim of that ultra-thin oil ring and bend it parallel to the piston skirt; so when the CYLINDER BLOCK seems to 'stick' for no reason, you pull the CYLINDER BLOCK back off to see why it won't go any further and find a bent oil ring.

...better...?

Yes thats the purpose of the oil ring expander. To expand the two oil rails for oil control.
Many will use a ring compressor to aid in compressing the ring pack during assembly.
Some use hose clamps and other means to accomplish the same task..


Most piston to cylinder wall clearance is a measurement..it’s in the service manual
Do you know what yours was after the 10seconds up and down with the glaze breaker…?
Cylinder taper..?

[Dr. Frankenstein]

TnB: I did use a bore gauge at the time (the little spring-loaded ones) and DID fit the rings and check the ring gap, and that was on spec; I don't have the numbers in front of me, but it was good.

Ozzy, yes, I did put the proper crosshatch on the walls; I'm familiar with the technique, having done this to a few Dreams. I used a triple-block hone. I have a 56 mm flex hone, but didn't use it as I've read they can be a little aggressive.

As it is now, I finally got the cam shaft and chain in and am going to continue with the build and see what I get after I get it all back together again. I am aware that compression numbers within 10 lbs of each other are 'good', but from what I've read they should be in the 150 lb range, yes...? Previously I tried to see if it would start on starting fluid, but it didn't, so I ran those original compression tests, added a little oil to #4 and the rest is history.

This time around I'll check the compression and report back before I try to start it - I did a clear-tube test on the carbs after I rebuilt those, and those were Good too, but doing a 'live-fire- exercise this time around with gasoline I think would give me better results than starting fluid.   

[HondaMan]

Your compression should go up after 50 miles or so. That will let the rings start to seat.

[Dr. Frankenstein]

I was wondering about that - so maybe all these problems I thought I had - the low compression, especially - could maybe have been due to just "new rings"?? And if I can get her started, I can expect to see increased performance as the rings seat in...?   I've just never had a bike that was that "slow" to perform...esp with new rings!

[grcamna2]

I was wondering about that - so maybe all these problems I thought I had - the low compression, especially - could maybe have been due to just "new rings"?? And if I can get her started, I can expect to see increased performance as the rings seat in...?   I've just never had a bike that was that "slow" to perform...esp with new rings!

Yes,get it started and run-it-in to 'seat' all the rings.

[Don R]

 These bikes are notorious for reading low during compression tests. Some think it's the volume in the test apparatus, a cold leak-down test may not show good numbers either. We often spend time chasing non-existent or unimportant problems. Sometimes it's as simple as letting the cylinders dry out.

[Ozzybud]

Are you using a compression gauge with a long or rubber hose?
Like I said earlier 100 is not low
 It's just a number.
Like hondaman said the combustion chamber is 18cc. If the volume in the hose or connecter is long.. say 10ccyou no longer have 9.5:1   compression ratio..
Cheap compression gages with long flexible hoses are crap. Especially Harbor Freight!

[Ozzybud]

I'm +1  with Don R. Likely you do not have a problem.
The original issue was due to having 1/2 oz of oil (15cc) in a 18cc chamber.

[Tracksnblades1]

TnB: I did use a bore gauge at the time (the little spring-loaded ones) and DID fit the rings and check the ring gap, and that was on spec; I don't have the numbers in front of me, but it was good.

Ozzy, yes, I did put the proper crosshatch on the walls; I'm familiar with the technique, having done this to a few Dreams. I used a triple-block hone. I have a 56 mm flex hone, but didn't use it as I've read they can be a little aggressive.

As it is now, I finally got the cam shaft and chain in and am going to continue with the build and see what I get after I get it all back together again. I am aware that compression numbers within 10 lbs of each other are 'good', but from what I've read they should be in the 150 lb range, yes...? Previously I tried to see if it would start on starting fluid, but it didn't, so I ran those original compression tests, added a little oil to #4 and the rest is history.

This time around I'll check the compression and report back before I try to start it - I did a clear-tube test on the carbs after I rebuilt those, and those were Good too, but doing a 'live-fire- exercise this time around with gasoline I think would give me better results than starting fluid.

Good to know everything checked out on spec and good..

What stones did you use in your triple block hone..?

Did you end up using CI or Honda rings…?

[Ozzybud]

You will never get a 150psi reading with thus gauge.

[Dr. Frankenstein]

Ozzy, that looks a LOT like the gauge I got a 250 lb compression on! I had to use an adapter to get it to fit in the bike, but - yeah, that looks a lot like it! (What's the deal with the gauge...?)

And Don, I'm kind of happy to hear that about these bikes; this is my first 500 Four, but I've had a lot of different bikes over the years, and the one thing I notice is every bike is different, and this is no exception.  But you've got me excited to see what happens!

[Ozzybud]

Ozzy, that looks a LOT like the gauge I got a 250 lb compression on! I had to use an adapter to get it to fit in the bike, but - yeah, that looks a lot like it! (What's the deal with the gauge...?)

The Gauge you have is fine. Like I said the number is for reference only and the number is not as important as the cylinders being similar in value.
You would get a higher reading with the steel attachments as shown below as there is less volume on the inside of the steel tube.

[Dr. Frankenstein]

I have those too; I'll try those when the time is right.

TnB, I think they were medium grit - I don't go too aggressive on my cylinders. And I went with CI rings...I had tried using rings from 4into1, but they were absolutely horrible, and the wrong size to boot - they were too big/thick and had the wrong oil rings! Despite my protestations and even PHOTOS of how wrong the rings were for the 1972 CB500 Four and Did Not Fit (even though they were advertised as such), they smugly told me "Well, we haven't had a problem yet, dude..."  So that was enough for me; I was lucky to get my money back. And actually, C-I's quality seems to be better, and the prices are really reasonable, too!

[HondaMan]

Ozzy, that looks a LOT like the gauge I got a 250 lb compression on! I had to use an adapter to get it to fit in the bike, but - yeah, that looks a lot like it! (What's the deal with the gauge...?)

The Gauge you have is fine. Like I said the number is for reference only and the number is not as important as the cylinders being similar in value.
You would get a higher reading with the steel attachments as shown below as there is less volume on the inside of the steel tube.

Ozzy: those look like the ones I had at my shop! Funny how good things never change?

[Tracksnblades1]

I have those too; I'll try those when the time is right.

TnB, I think they were medium grit - I don't go too aggressive on my cylinders. And I went with CI rings...I had tried using rings from 4into1, but they were absolutely horrible, and the wrong size to boot - they were too big/thick and had the wrong oil rings! Despite my protestations and even PHOTOS of how wrong the rings were for the 1972 CB500 Four and Did Not Fit (even though they were advertised as such), they smugly told me "Well, we haven't had a problem yet, dude..."  So that was enough for me; I was lucky to get my money back. And actually, C-I's quality seems to be better, and the prices are really reasonable, too!

That CI ring pack may be a pretty modern and good ring pack.. If indeed it’s top ring is a gas nitride coated forged steel ring and  a steel phosphate 2nd ring and a nitride three-piece oil ring. They’ll seat quick. Especially with the recommended proper two step  plateau honing. Most gas/nitrided recommend starting with a 320-400 grit crosshatch valley. Finishing with a 600grit or a brush for the proper plateau depth/percentage.. To achieve the optimal RA finish as rec by the ring manufacturers.

Did CI include the cylinder wall prep with proper RA finish range with their ring sets..

With this two stage plateau honing requirement of these modern rings, my old stiff hone is rarely used..
Excepting old chrome rings…I like the wiseco ring packs (not the XA). I have a local shop with a sunnen
hone put the proper crosshatch angle, valley depth and plateau percentage on the cylinder walls..

I still break them in like an old chrome rings..no since overheating them right of the start…

[Dr. Frankenstein]

I think I should be good this time around; when I get it all back together I'll take another compression test, without any added oil and see what I get. That bike has a very small squish zone!

[Ozzybud]

I think I should be good this time around; when I get it all back together I'll take another compression test, without any added oil and see what I get. That bike has a very small squish zone!

Just run it instead. You only need to do a compression test if you have a problem

[Dr. Frankenstein]

A problem like what...?

[Ozzybud]

Lack of power, blowing blue smoke out of the tail pipes. You have new rings and freshly honed cylinder walls.start it up and start breaking them in.

[Dr. Frankenstein]

I got it all buttoned up and ran a compression test again (with no oil this time), and this time got 105 on #1, 110 on #2, 110 lbs on #3 and 105 on #4. It does have fresh oil in the crank case, up to the second level on the stick so I know it has oil in it; I figured by this time the pump should have pumped some oil through it, so I took out the air filter and gave it a shot of starting fluid into the airbox - it 'chuffed' a few times but didn't want to catch.

I do have a rather weak spark across all four plugs (with new coils), and from what everyone is telling me here there should be enough compression to get it to start, but so far no luck.  When I put the cam shaft in I made sure it was installed correctly, with the notch on the end parallel to the cylinder head seam and the points set at the T mark on 1&4...I have a fully charged battery, too, but I'm wondering if it would be better to put some gas in it and see if anything changes...I'll re-check my timing and points gap, but any ideas? What am I missing?

I've read that the coil mounts need to be grounded to the frame as well; I'll check again, but would any paint on the frame where the coils mount degrade the spark? I'm thinking that if the whole bike is indeed a 'ground', that might be a factor too....