P500 Top Dead Center

[MarineTanker]

Is there an appreciable difference in piston stroke when determining TDC ??
I just did my 100 mile valve clearance check on my Pioneer 520 and determined TDC simply by rotating the crank until the piston was at TDC. However, I've been "told" TDC should be the TDC on the COMPRESSION STROKE, not the exhaust stroke.

 

[Admin]

 

[KyGal83]

I can't help you with this... Someone who can will be along shortly. @906UP or @Neohio ,

But every time I hear someone refer to TDC. I think of this... IYKYK..

 

[906UP]

Is there an appreciable difference in piston stroke when determining TDC ??
I just did my 100 mile valve clearance check on my Pioneer 520 and determined TDC simply by rotating the crank until the piston was at TDC. However, I've been "told" TDC should be the TDC on the COMPRESSION STROKE, not the exhaust stroke.

Technically, yes there is a difference. You should check valves at TDC of comp stroke. Then you are guaranteed that both valves are completely closed. If you check it between the exhaust/intake stroke (180° out on the cam) you may get bad readings as some cams have some overlap or you could be on the ramp down/up of the profile. That said, the P5/P5.2 is a very simple powerplant, I doubt you'll have any issues if you checked it like that.

 

[MarineTanker]

Technically, yes there is a difference. You should check valves at TDC of comp stroke. Then you are guaranteed that both valves are completely closed. If you check it between the exhaust/intake stroke (180° out on the cam) you may get bad readings as some cams have some overlap or you could be on the ramp down/up of the profile. That said, the P5/P5.2 is a very simple powerplant, I doubt you'll have any issues if you checked it like that.

Yeah, my brother (master mechanic for 45 years) told me about this AFTER I did my valve check and adjustment. He basically told me the same as you that he doubted I would have any issues. BTW, after the job, I started the engine and I swear it caught earlier than before the adjustment. Took it out for a ride around, and it's purring. So I think I'm ok.
I really appreciate your response!
Thanks!

 

[Hello_Darkness]

Yeah, my brother (master mechanic for 45 years) told me about this AFTER I did my valve check and adjustment. He basically told me the same as you that he doubted I would have any issues. BTW, after the job, I started the engine and I swear it caught earlier than before the adjustment. Took it out for a ride around, and it's purring. So I think I'm ok.
I really appreciate your response!
Thanks!

If you had adjusted the valves on the exhaust stroke (or overlap) then they would've been very tight when inserting a feeler gauge.

If loosened at that point, they would be very loose on compression and would be noisy as heck while running.

The easiest way to tell if your on the right stroke is to grab the rocker and try to move it. If it's solid, your 180 degrees out and not on compression.

 

[DRZRon1]

Yeah, my brother (master mechanic for 45 years) told me about this AFTER I did my valve check and adjustment. He basically told me the same as you that he doubted I would have any issues. BTW, after the job, I started the engine and I swear it caught earlier than before the adjustment. Took it out for a ride around, and it's purring. So I think I'm ok.
I really appreciate your response!
Thanks!

Did you adjust anything?


Good brother - if only he woulda been there

 

[MarineTanker]

If you had adjusted the valves on the exhaust stroke (or overlap) then they would've been very tight when inserting a feeler gauge.

If loosened at that point, they would be very loose on compression and would be noisy as heck while running.

The easiest way to tell if your on the right stroke is to grab the rocker and try to move it. If it's solid, your 180 degrees out and not on compression.

I'm a bit confused by "grab the rocker and try to move it". How so? Are you talking about turning the crankshaft? I've had a few responders say they don't think there's an appreciable difference between TDC on either stroke on these particular engines. I would hate to take the damn thing apart again just to check. I've run it around after my job and it's purring without any tapping. Actually starts first crank now as opposed to before my adjustment when it took 3 to 5 cranks to fire up, which might just be coincidental.

 

[DRZRon1]

I'm a bit confused by "grab the rocker and try to move it". How so? Are you talking about turning the crankshaft? I've had a few responders say they don't think there's an appreciable difference between TDC on either stroke on these particular engines. I would hate to take the damn thing apart again just to check. I've run it around after my job and it's purring without any tapping. Actually starts first crank now as opposed to before my adjustment when it took 3 to 5 cranks to fire up, which might just be coincidental.

What they mean is grab the actual rocker where the pushrod pushes against - at TDC with the proper clearance - it will move a little since there is clearance -

if u checked it when it was 180 out - the rocker shoulda been solid with no wiggle


did u adjust anything ?


In general - without data - 99% dont check the valves - no saying thats right - rule of thumb is check when noisy - its a Honda - skinny pedal down and send it

 

[MarineTanker]

What they mean is grab the actual rocker where the pushrod pushes against - at TDC with the proper clearance - it will move a little since there is clearance -

if u checked it when it was 180 out - the rocker shoulda been solid with no wiggle


did u adjust anything ?


In general - without data - 99% dont check the valves - no saying thats right - rule of thumb is check when noisy - its a Honda - skinny pedal down and send it

Yeah, I adjusted both valves. Such a PITA to just expose the engine to work on it! Dealer told me it would be a $420.00 job! No way I'm doing that. I'm probably going to leave it alone now until and unless I hear anything tapping.

 

[906UP]

Yeah, I adjusted both valves. Such a PITA to just expose the engine to work on it! Dealer told me it would be a $420.00 job! No way I'm doing that. I'm probably going to leave it alone now until and unless I hear anything tapping.

Good deal, leave it alone, it's fine. I didn't adjust the valves on my '16 until I ripped it apart for a BBK in '19, they haven't been touched since.

 

[hondabob]

On the compression stroke both valves will have play. Be sure to turn the crank clockwise. I'm at 4,000 miles on my 520 and will check the valves again. They needed adjustment after my break in. Both just need a slight adjustment.

 

[Hello_Darkness]

I'm a bit confused by "grab the rocker and try to move it". How so? Are you talking about turning the crankshaft? I've had a few responders say they don't think there's an appreciable difference between TDC on either stroke on these particular engines. I would hate to take the damn thing apart again just to check. I've run it around after my job and it's purring without any tapping. Actually starts first crank now as opposed to before my adjustment when it took 3 to 5 cranks to fire up, which might just be coincidental.

Anyone who says that TDC compression/overlap has no difference on any 4 stroke engine is an idiot and shouldn't be working on any engine.

On overlap, both valves are slightly open, hence the term "overlap".If you grap the rocker with your fingers and try to wiggle it, they shouldn't move. Also there will be no clearance between the rocker and valve tip.

On TDC compression, both valves are closed and your on the base circle of the cam meaning off the lobe and the clearance can be set/checked.

 

[MarineTanker]

Anyone who says that TDC compression/overlap has no difference on any 4 stroke engine is an idiot and shouldn't be working on any engine.

On overlap, both valves are slightly open, hence the term "overlap".If you grap the rocker with your fingers and try to wiggle it, they shouldn't move. Also there will be no clearance between the rocker and valve tip.

On TDC compression, both valves are closed and your on the base circle of the cam meaning off the lobe and the clearance can be set/checked.

As you seem to know a great deal about these engines, and I'm more of a carpenter/plumber type who just tries to do all I can by myself, I need to ask another question (and show my ignorance).

Q. If I now check settings with my feeler gauges and find the first setting I check to be @ .009 & .006, and I turn the crank to the next TDC and find they are wider than .009 & .006, (or conversely) can I "assume" that I set them improperly? Then, if so, when I turn the crank to the compresson stroke TDC and properly set the gaps, what do I do about the "improper" settings I made on the exhaust stroke? I have no idea what t hey should be.

 

[Hello_Darkness]

As you seem to know a great deal about these engines, and I'm more of a carpenter/plumber type who just tries to do all I can by myself, I need to ask another question (and show my ignorance).

Q. If I now check settings with my feeler gauges and find the first setting I check to be @ .009 & .006, and I turn the crank to the next TDC and find they are wider than .009 & .006, (or conversely) can I "assume" that I set them improperly? Then, if so, when I turn the crank to the compresson stroke TDC and properly set the gaps, what do I do about the "improper" settings I made on the exhaust stroke? I have no idea what t hey should be.

If you set the clearance on compression, the overlap will return to normal.

By adjusting on the overlap, you would've made the clearance too large on compression.

When you checked them the first time were they tighter then the specification? If you loosened them then it most likely was on overlap..

 

[MarineTanker]

If you set the clearance on compression, the overlap will return to normal.

By adjusting on the overlap, you would've made the clearance too large on compression.

When you checked them the first time were they tighter then the specification? If you loosened them then it most likely was on overlap..

Yeah, they were tighter than specs. So, I'm assuming I did the adjustment on exhaust not compression.
So again, now that I opened them too far on exhaust and set them there, I plan to get back in and check gaps on both strokes. Wouldn't my screwup mean that the gaps on compression are now way too open? If so, back to my original question, if I then get a set of too large gaps on one of my trial TDC strokes, can't I assume that is TDC at compression? If so, and I set those to spec, do I need to do anything to the gaps on exhaust or will my adjustment on compression bring the exhaust stroke gaps back to spec?

 

[Hello_Darkness]

Yeah, they were tighter than specs. So, I'm assuming I did the adjustment on exhaust not compression.
So again, now that I opened them too far on exhaust and set them there, I plan to get back in and check gaps on both strokes. Wouldn't my screwup mean that the gaps on compression are now way too open? If so, back to my original question, if I then get a set of too large gaps on one of my trial TDC strokes, can't I assume that is TDC at compression? If so, and I set those to spec, do I need to do anything to the gaps on exhaust or will my adjustment on compression bring the exhaust stroke gaps back to spec?

You need to find at which TDC your valves are the loosest, then adjust at that position.

The exhaust/overlap will fix itself, since your taking the slack up on the base circle or on the compression stroke of TDC.

And just an FYI, I only seem like I know this stuff because it's literally my job and has been for 16 years.

 

[MarineTanker]

You need to find at which TDC your valves are the loosest, then adjust at that position.

The exhaust/overlap will fix itself, since your taking the slack up on the base circle or on the compression stroke of TDC.

And just an FYI, I only seem like I know this stuff because it's literally my job and has been for 16 years.

Gotcha! That's kinda what I was trying to say in my own thousand word essay! Seemed logical to me, but nice to have an expert confirm my thought . Thanks again!!

 

[john790]

SSSSSSSSSSSSSSSSSSSSSoo what valves did you move and how much.I always ck before and after.And remember a sheet of paper is close to .003

 

[MarineTanker]

Yeah, I know now that I set them at TDC of the wrong stroke. I need to do it all over again and set them at TDC on the compression stroke. Pain in the ass to have to do the job again. At least this time, it won't take me 3 hrs! I have a set of "L" feeler gauges, so I'm all set there...lol