Help with tuning.

brian4.2 said:

I dont remember, its been a couple years. I can measure once its apart. What am i looking for?

What else could it be?

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If you had measured the ring end gaps, a gross bore dimension error would have jumped out at you.

You can find end gap values in the workshop manual, I am mobile at the moment.
I can look it up later.

brian4.2 said:

I dont remember, its been a couple years. I can measure once its apart. What am i looking for?

What else could it be?

Click to expand...

I do not want to insult/anger/annoy, it COULD be a broken ring, overlapped oil ring expander, on & on....
TEST, don't guess.
You have feeler gages, correct?

Thanks I appreciate any input, I have been sitting on this for almost 3 years. I suspected a broken ring, or improperly installed. I would think one side but if I had it wrong its possible both sides. I will know in a few days. I was a little harsh in my guess what caused the low compression, I amended my post.

I have all the tools.

I would not be in a hurry to go 60 over. Compression test can be difficult on kick starters.
Did you hold the throttle open?
Leak down is better.

If it fails leak down, you can hear where the air is escaping.
If it's in the head, you'll hear it. Go from there.
Was there head work done?

Once your satisfied with the head, pull the barrels and check ring gap as previously mentioned.
With barrels pulled, a sneak peak at the cam is good idea.
New rings and maybe hone go a long way.
Again, I would not be in hurry to rebore. Absolute last resort....

What do you mean by rough running?

Jim Comstock rebuilt the head. I have a CNW E-start, began each reading with a fully charged battery. I will do the leak down in the morning after the couple of tablespoon of oil work their way out.

Again there is only 50 miles on a 100% rebuild.

Rough running , misfire on the right side, spitting oil visibly out the exhaust nut and the header to silencer union.

To Elephant rider Pistons are JCC CS-0135 +.020 (my mistake not 40 over) Rings are Hastings CS-0116A +.020

I'm reading that the compression test should run around 125psi, is this correct?


Thank you all, Brian

brian4.2 said:

Jim Comstock rebuilt the head. I have a CNW E-start, began each reading with a fully charged battery. I will do the leak down in the morning after the couple of tablespoon of oil work their way out.

Again there is only 50 miles on a 100% rebuild.

Rough running , misfire on the right side, spitting oil visibly out the exhaust nut and the header to silencer union.

To Elephant rider Pistons are JCC CS-0135 +.020 (my mistake not 40 over) Rings are Hastings CS-0116A +.020

I'm reading that the compression test should run around 125psi, is this correct?


Thank you all, Brian

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My 850 tested around 155 psi both sides after rebore to 40 thou....that was with a warm engine, wide open throttles, and a good many kick overs. Did make a bit of smoke for first 200-400 miles...Running great for past 5k miles this season.

I'd be fast to pull the head , inspect everything , particularly the valve seals , the guides in the head for any motion . The head gasket for leakages too . Failing that check I would pull the barrels and inspect .

In one of the videos, you are seriously pumping oil ( wetsumping - pumping oil sitting in the sump). They all do that when the sump is full. Once all the oil is out of the sump, you may try testing for vaccum leaks while it is running.

Spray carb cleaner around intake manifolds when running and note any changes in idle.

Swap in new plugs, get a new mixture reading.

BTW, what are your plugs gapped at?? Gaps look too wide to me.

Rule out all the easy stuff first, before going after the rings.

Any luck?

Ok progress finally. So you dont have to read the whole thread I'll describe the bike and problems. I bought the bike as a beater in 2016, only needed everything, perfect for a project, I did see a running video. I think I paid $3,000
I did a 100% restoration.
I handled every part on the bike, either refinished or replaced. Polished every chrome and aluminum part.

1972 Combat Commando. Less than 50 miles since completion.

Cases. superblend bearings,
JS-1 Camshaft.
Did the revision on the drive side case to improve the oil flow.
Blocked all the holes from the timing side into the crankcase and drilled a 1/4" hole under the oil pump.
Sent the timing cover to AMR for the Nortec revision and had them rebuild the oil pump.
Comstock reed valve off the back of the case.
Jim Comstock rebuilt the head.
+20 on the JCC pistons with Hastings rings
New Amal premiers 932s middle grove , 220

Last time I ran it the right side was spitting oil out the cam seal @ the Electronic Ignition. Spitting oil out the exhaust port and leaking at the exhaust nut and the header to muffler joint was weeping a lot of oil. I drained the sump and out comes 20oz of oil.

How does a wet sumping condition put oil in the exhaust ports?

So I have pulled the head and taken a lot of pictures.

brian4.2 said:

Ok progress finally. So you dont have to read the whole thread I'll describe the bike and problems. I bought the bike as a beater in 2016, only needed everything, perfect for a project, I did see a running video. I think I paid $3,000
I did a 100% restoration.
I handled every part on the bike, either refinished or replaced. Polishednevery chrome and aluminum part.

1972 Combat Commando. Less than 50 miles since completion.

Cases. superblend bearings,
JS-1 Camshaft.
Did the revision on the drive side case to improve the oil flow.
Blocked all the holes from the timing side into the crankcase and drilled a 1/4" hole under the oil pump.
Sent the timing cover to AMR for the Nortec revision and had them rebuild the oil pump.
Comstock reed valve off the back of the case.
Jim Comstock rebuilt the head.
+20 on the JCC pistons with Hastings rings
New Amal premiers 932s middle grove , 220

Last time I ran it the right side was spitting oil out the cam seal @ the Electronic Ignition. Spitting oil out the exhaust port and leaking at the exhaust nut and the header to muffler joint was weeping a lot of oil. I drained the sump and out comes 20oz of oil.

How does a wert dumping condition put oil in the exhaust ports?

So I have pulled the head and taken a lot of pictures.

View attachment 105087

Click to expand...

Cam seal in backwards? Breather blocked? (Cap off the oil tank, finger loosely over the breather return, kick - should feel air. 20oz not enough to fill the exhaust area - drains blocked? Rocker covers off, pour in oil - does it drain away?

Some motorcyclists might do better if they bought a modern bike and paid for it to be serviced. If something changes on my bike, I just pull it apart to find out what is wrong. I have never done a compression test in my life, or used a dyno for tuning. I know I can get my bike right without doing any of that. If I get stuck, I sometimes re-engineer the whole kit and caboodle.
When you own old motorcycles, the mindset involved needs to be different. I would never give any part of my bike to somebody else to rebuild.
Years ago a young kid offered to rebuild my Triumph motor for me. I felt like strangling him. Some of the guys who work with old bikes as a business are OK - but not many.

Your head is off now. There is a drain back hole on the right rear of barrel. Check to see if it is clear.

Pics #1

Pics #2

Pics #3 sorry about too many pictures, someone might see something

MichaelB said:

Your head is off now. There is a drain back hole on the right rear of barrel. Check to see if it is clear.

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Thank you Michael. The hole is clear, I didn't use any sealer on the head gasket. I will be pulling the barrel to measure the ring gaps. The bores look perfect, I would expect some scoring if I broke a ring installing, I did it by hand without a compressor.

acotrel said:

Some motorcyclists might do better if they bought a modern bike and paid for it to be serviced. If something changes on my bike, I just pull it apart to find out what is wrong. I have never done a compression test in my life, or used a dyno for tuning. I know I can get my bike right without doing any of that. If I get stuck, I sometimes re-engineer the whole kit and caboodle.
When you own old motorcycles, the mindset involved needs to be different. I would never give any part of my bike to somebody else to rebuild.
Years ago a young kid offered to rebuild my Triumph motor for me. I felt like strangling him. Some of the guys who work with old bikes as a business are OK - but not many.

Click to expand...

Whats the fun in having a new bike? Im not afraid to have someone work on the parts I have no knowledge of. Im not afraid to use this great resource and ask questions and take advice.

There are some curmudgeons on here that think they invented the motorcycle, don't let'm get you down. You are learning all the time and it is no shame to send parts out to experts.

brian4.2 said:

Pics #3 sorry about too many pictures, someone might see something

Click to expand...

Appear to be burning a lot of oil on the drive side. Intake valve seal - rocker spindles facing inward - rings upside down - Idling on the side stand for a long time - intake drane down through cylinders to timing chest blocked. Doesn't appear to be a head gasket leak (push rod tunnel into cylinder). Which side was leaking out of the exhaust.

The pictures are good but a few more specifics are needed.

marshg246 said:

Appear to be burning a lot of oil on the drive side. Intake valve seal - rocker spindles facing inward - rings upside down - Idling on the side stand for a long time - intake drane down through cylinders to timing chest blocked. Doesn't appear to be a head gasket leak (push rod tunnel into cylinder). Which side was leaking out of the exhaust.

The pictures are good but a few more specifics are needed.

Click to expand...

Thanks Greg

It's never on the side stand. I'll check the ring orientation when the barrel comes off, and the drain. And the ring gaps. The right side is spitting oil, more like puking. But like i said, there was 20oz of oil in the sump right after this condition. I assumed the AMR revisions helped with that but have definitely been long intervals between me firing the bike up.