Compression test to diagnose rod knock or rattle?

Hi all,

I have a 2000 Yammy F15ESHY that I have finally gotten back up and running. It's been performing well with no hesitation, sputters, etc. However, in WOT, I've noticed a "pinging" noise that actually causes the engine to move, like if you were standing next to it and gave it a little "bump" to the side in one direction. It's not consistent, just more of an erratic ping that only occurs at WOT. If I back just slightly off, it goes away. Also, there seems to be a faint rattle, but I can't tell if it's related or if it's truly a rattle. So my question is; would a compression test be a good indicator of a knock or rattle if the compression is off or is there another way to go about this? Also, I used Champion plugs instead of the NGK's because they were the only ones available for purchase at the time that I needed them. Could they be the culprit?? Like I said, fine in every other throttle position except WOT. Thanks in advance!

Re: Compression test to diagnose rod knock or rattle?

Compression test won't help you.

-Check you maximum timing.....could be set too early.

-You might want to inspect what goes on under the flywheel. Look for loose magnets or rub marks.

-You also might be concerned with Double firing. If you have access to a timing lite with built in tach, see if the RPM varies dramatically.

-Plugs could do it as well if the heat range is miles off. Too hot of a plug could cause detonation.

-do a thorough decarb. It also can cause detonation from hot spots.

IMO

Re: Compression test to diagnose rod knock or rattle?

Hi Schematic,

The heat range on the plugs is the same (6) and I had definitely suspected loose magnets, I just more concerned about tackling the detonation issues first. What exactly is maximum timing and how do I check it? Also, I've heard arguments from two different schools of thought on decarbing; Sea Foam or Ringfree? Is there a difference? Thanks!

Re: Compression test to diagnose rod knock or rattle?

JonnyPartTime said:

Hi all,

I have a 2000 Yammy F15ESHY that I have finally gotten back up and running.

Click to expand...

What exactly did you do to this thing?

Re: Compression test to diagnose rod knock or rattle?

JonnyPartTime said:

Hi Schematic,

The heat range on the plugs is the same (6) and I had definitely suspected loose magnets, I just more concerned about tackling the detonation issues first. What exactly is maximum timing and how do I check it? Also, I've heard arguments from two different schools of thought on decarbing; Sea Foam or Ringfree? Is there a difference? Thanks!

Click to expand...

If you have loose parts hitting things ,you need to take care of that first before running it any more.

Timing can be checked with a timing light, just like any automotive motor.
service manual will give all specs and procedures, pick one up for your motor.

Sea foam has worked well for me

Re: Compression test to diagnose rod knock or rattle?

Thanks Yam, I've heard a lot of people say that Sea Foam is the way to go. It's not a loud rattle, is what I meant to say. To be honest, I might just be imagining it. I tried to record it to post but the sound doesn't register on the recording. I've got a service manual but it doesn't mention anything about maximum timing. Is it maybe called something else? The timing is fine, otherwise.

Schematic: I blew the head gasket at the beinning of the summer and wound up messing up the timing when I put it all back together, it was such a stupid mistake. I blame it on the Charleston summer heat Anyway, I wound up bending the valves and it took me all summer to hunt down new ones (backordered for over a month). But it was one thing after another; fuel pumps, bad primer bulbs, name it. Now it runs great, it just has that annoying spontaneous ping at WOT. I'm gonna check the magnets in the morning and decarb it, then go from there.

Thanks again for everyone's help!!

Re: Compression test to diagnose rod knock or rattle?

wouldn't hurt to pull the plugs out and inspect the tops of the pistons for impact marks. Do it in the dark with a small flashlite. Kinda like CSI !!LOL

Re: Compression test to diagnose rod knock or rattle?

Manual should give idle and WOT timing in the spec table.

There is the timing of the cam that you messed up on at 1st and then there is the timing of when the plugs are fired

If you have had this thing open then you should know if there was a lot of carbon in it that would affect preignition.

hard steel valves hitting aluminum pistons can damage/crack them, hope they are OK

Re: Compression test to diagnose rod knock or rattle?

Schematic: Hahaha! Ok man, the neighbors have definitely seen me out doing werider things in the middle of the night

Yam: Oooh, yeah, there are specs for WOT timing. Sorry, not sure how I failed to make that connection. The pistons looked pretty good when I had the cylinder head off. There was definitely some carbon in there but I had nothing in memory to compare it to (first time opening an engine up that far). I honestly didn't know that carbon could cause preignition until a few days ago. Do you recommend using the spray SeaFoam through the carb or the 16 oz in 3/4 gal of gasoline method?

Re: Compression test to diagnose rod knock or rattle?

I did both and even pulled plugs and shot some in that way too.
Let it sit over night and then ran it off and on on the water with the can in 3/4 gal fuel
had black stuff run out of prop even when I parked in drive way, should have put a pan under it

I picked up the boat and motor 3rd hand and someone had drilled out the jets in carbs ( took some time to find that),so there was a lot of left over junk and carbon in cylinders and exhaust

If there is enough carbon it can get glowing red hot and fire off the fuel, but a little will not hurt unless motor is running super hot

Pistons hitting and bending valves can hurt pistons, bend rods, and cause bearing damage
So the best of luck on your motor

Re: Compression test to diagnose rod knock or rattle?

Thanks for the info Yam. Anything I can do to test for damage beside visual inspection?

Re: Compression test to diagnose rod knock or rattle?

not that I can think of right of the bat

Re: Compression test to diagnose rod knock or rattle?

I figured. Thanks again, though.