No Start/ No Compression

[rkrcpa]

Put the bike (stock '07 FLHT) in the shop trying to diagnose an intermittent no start issue. It's been in the shop before for this issue but the problem never occurs when it's in the shop, until today. Basically, it appears that there is no compression on the rear cylinder hence it doesn't fire. The question now is what do I want them to do to diagnose why there is no compression.

For that I turn to the HTT brain trust. I am at a loss as to what would cause an intermittent loss of compression in the rear cylinder. When it runs it runs strong and quiet so it doesn't seem like something is broken. This happens at random times, sometimes the first start of the day sometimes the last gas stop on a 1000 mile day. Literally no rhyme or reason to it.

I'd rather not have them start pulling "Potty mouth" apart just in the hope that they find something.

Thoughts?

[smoserx1]

Sticking valve?  Easy start cam malfunctioning intermittently?  Can't imagine pistons/rings behaving this way.

[Hossamania]

Any modifications to the bike, motor?

[rkrcpa]

Any modifications to the bike, motor?

Factory original (I know, shame on me)

[Ohio HD]

Agree, probbaly a sticky valve.

[Hossamania]

Any modifications to the bike, motor?

Factory original (I know, shame on me)

The rarest of all Harleys.

Good luck in getting to the bottom of the problem.

[838]

I'd rather not have them start pulling "Potty mouth"
apart just in the hope that they find something.

Thoughts?

Could some sea foam help if it's a sticky valve?  some in the tank, some through the manifold???

[rigidthumper]

Bad cams- had it happen on more than one 2007- the lobes are a light press fit, and they have come loose- cam lobe will indeed spin on the shaft...

[rkrcpa]

What gets me is the fact that it runs great when it finally starts.

Hard to understand how there could be a catastrophic failure that goes away once the engine starts.

[Coyote]

Well it's not too hard to pull the CAM plate and you probably need too look at the tensioners anyway on an 07. Course it's hard to say since you gave so few details. Like mods, mileage etc.

[fleetmechanic]

That was the first year with ACRs. Could one be staying open?

[Ohio HD]

In 2007 only CVO bikes had compression releases.

[rkrcpa]

The bike has 45,000 miles on it with no mods at all. It still has the stock intake and exhaust. No compression releases, no cam upgrades, nothing.

Looks like the plan is to work our way down the cylinder until something is found. Once the cam plate is removed it's going to mean cam upgrade. I've got a set of SE 255's sitting on the shelf waiting.

[rigidthumper]

I'd start with the cam plate (since you have replacements awaiting).

[HogMike]

Put the bike (stock '07 FLHT) in the shop trying to diagnose an intermittent no start issue. It's been in the shop before for this issue but the problem never occurs when it's in the shop, until today. Basically, it appears that there is no compression on the rear cylinder hence it doesn't fire. The question now is what do I want them to do to diagnose why there is no compression.

For that I turn to the HTT brain trust. I am at a loss as to what would cause an intermittent loss of compression in the rear cylinder. When it runs it runs strong and quiet so it doesn't seem like something is broken. This happens at random times, sometimes the first start of the day sometimes the last gas stop on a 1000 mile day. Literally no rhyme or reason to it.

I'd rather not have them start pulling "Potty mouth"
apart just in the hope that they find something.

Thoughts?

I had an '09 with a similar issue years ago. We found the rear exhaust guide had stuck intermittently on the stem until it finally pulled loose from the head. Replaced the guide, valve and serviced the others to make sure everything was good.
Suspect was either poor clearance from the factory and/or excessive heat.

Just a thought.

[Sycho01]

Just do a leak down test and find the problem. Why guess? Ion sensing ignition, no compression, no ignition.

[PoorUB]

Pretty hard to do a leak down with zero compression. Although the air coming out of the intake, exhaust or oil pan would give a good idea what is wrong, but it really doesn't matter. Stuck intake, exhaust, or blown piston and the head still has to come off so why bother?

[smoserx1]

Hard to understand how there could be a catastrophic failure that goes away once the engine starts.

My thoughts exactly.  Did the shop actually do a test for compression or a leak down test?  I sure hope they didn't just assume since there was no fire there was no compression.  Something like a spun cam lobe or a hole in a piston seems like it would be permanent, not intermittent.  Is the problem just when starting or does the cylinder actually drop out while riding (or both).  It looks to me like if the valve was stuck open very much the piston might hit it.  Regardless, try and rule out an intermittent electrical issue before tearing the engine apart.

[Chief0299]

Hang on a sec... why are you saying no compression? Have you done a compression check, or is that what the DTC code comes up saying?

[rkrcpa]

Hang on a sec... why are you saying no compression? Have you done a compression check, or is that what the DTC code comes up saying?

Hold your thumb on the spark plug hole and there is no compression. Zero, zilch, nada. Yet when it does eventually fire it runs just fine.

That is why I am at a loss for an explanation. It is a very unusual intermittent symptom. It could very well start with no problem on the next try.

[HogMike]

Hang on a sec... why are you saying no compression? Have you done a compression check, or is that what the DTC code comes up saying?

Hold your thumb on the spark plug hole and there is no compression. Zero, zilch, nada. Yet when it does eventually fire it runs just fine.

That is why I am at a loss for an explanation. It is a very unusual intermittent symptom. It could very well start with no problem on the next try.

No ACR?

valve sticking in guide?
Seen it more than once.

When it DOES run, how does it sound?
Stock bike with stock muffler and intake?

[Appowner]

Bad cams- had it happen on more than one 2007- the lobes are a light press fit, and they have come loose- cam lobe will indeed spin on the shaft...

But if it does that wouldn't there be a noticeable change in engine performance as the lobe that moved would effectively have changed the timing for that cylinder?

I see what you mean with the lobe slipping but I would think there would be some more obvious symptoms.

[rkrcpa]

Hang on a sec... why are you saying no compression? Have you done a compression check, or is that what the DTC code comes up saying?

Hold your thumb on the spark plug hole and there is no compression. Zero, zilch, nada. Yet when it does eventually fire it runs just fine.

That is why I am at a loss for an explanation. It is a very unusual intermittent symptom. It could very well start with no problem on the next try.

No ACR?

valve sticking in guide?
Seen it more than once.

When it DOES run, how does it sound?
Stock bike with stock muffler and intake?

Once it starts it runs and sounds normal, as if nothing had happened. The only thing I can think is a valve sticking, but the intermittent nature is what is baffling.

[rigidthumper]

Bad cams- had it happen on more than one 2007- the lobes are a light press fit, and they have come loose- cam lobe will indeed spin on the shaft...

But if it does that wouldn't there be a noticeable change in engine performance as the lobe that moved would effectively have changed the timing for that cylinder?

I see what you mean with the lobe slipping but I would think there would be some more obvious symptoms.

These went from running to not running, with no compression on one cylinder. No start/no run until repaired, so different from your scenario.

[PoorUB]

Could have dropped a valve seat too. Not sure on a Harley if there is piston clearance, but on other engines I have had similar running problems and one of the valve seats was more than loose. Sometimes it would fall in place and run, other times get cocked over a bit and hold the valve open.