zero compression on cyl 3 on chrysler 115

i have posted before about the revs not pulling past 2000 rpm, but yet the boat pulls okay and will run at 25 mph at 1500 rpm and will do a touch over 30 at just under 2000 rpm....so I can live with that. But I did a compression check, the 3rd plug has no oil or soot at all...clean like new and the cylinder static comprssion is ZERO...not a wiggle in the gauge. the other three range from 125 to 132....what gaping hole creates a zero??? a big hole in the piston? and wouldnt it still get some burn and dirty up that plug? or is there a relation tween no compression and a clean plug? Thanks...

Re: zero compression on cyl 3 on chrysler 115

No fire on a plug is a clean plug.3rd plug down is the fuel pump plug.No comp is a no fuel on that cylinder,meaning no rev's/no fuel.
Motor 77-84 might be worth fixing.
Pull the head and see what damage is there before you ruin the block completly.Do a spark test too.
Could be a hole or the side of the piston gone.Maybe the head gasket.

Re: zero compression on cyl 3 on chrysler 115

There is no way you can run 25 mph at 1500 rpm ... the prop pitch and the revs just wont allow that to happen so your rev counter is way way out..

suspect you have a hole in the piston..do you have CDI igniton and using wire plugs CAN be a big mistake

Re: zero compression on cyl 3 on chrysler 115

i have the magnapower ign.
Been working on that theory about the tach, wiring is good, where does it draw its pulse from..could be the missing spark from cyl 3 is throwing the rpm pulse off?? and yes...to hit zero psi it aint no head gasket leak is it. How does this sound...maybe there is a fuel delivery problem to that cylinder , so no oil then also...
I have some season left and dont want to to miss it...if I keep running it, do I lube that cylinder to prevent it seizing?

Re: zero compression on cyl 3 on chrysler 115

You can throw some oil in there but it's gonna have gas injected on every revolution.
That motor might last a day or a month.It can also ruin the other cylinders if parts start flyin.
Profile?? You might be close to someone who can help.J

Re: zero compression on cyl 3 on chrysler 115

Supergas, I think we have all been there, you know the last few weeks of summer, old man winter creeping in, squeezing every last drop of that warm summer goodness out, and us boaters trying to outrun the inevitable. But seriously, unless you have buckets of money to throw at a new OB you need to address the problem. Also, with a dead cylinder you will lose alot of performance anyway, so spend one of the last days of summer pulling the head to assess the damage. Then you will know whether you need to break out the kiddie pool in the front yard, or put a new head gasket on and get back out there.

Re: zero compression on cyl 3 on chrysler 115

The tacho signal comes from the alternator winding so nothing to do with igniton ...you still did not answer if you were using wire plugs on a CD igniton ...To be FRANK I know someone who will go mad but if its got a hole in a piston tig weld it up in situ and use the right plugs and mixture settings in future ....been there done that

Re: zero compression on cyl 3 on chrysler 115

The tacho signal comes from the alternator winding so nothing to do with igniton ...you still did not answer if you were using wire plugs on a CD igniton ...To be FRANK I know someone who will go mad but if its got a hole in a piston tig weld it up in situ and use the right plugs and mixture settings in future ....been there done that

Re: zero compression on cyl 3 on chrysler 115

okay the plugs...they are odd looking buhw I think, anyhow they are flat on the center electrode, and have no side electrode. i trust that is the right kind for the magnapower ign.
next , the kiddie pool eh...ha....grrrr. seriously though ...it aint no stinking head gasket ...that would be nice...but..a leaky head gasket in all likelyhood would not report a zero compression but rather a lower compression..and its a ZERO...texas size leak!
next the fuel discharge into the bad cylinder...thats what I need to know...what could cause zero compression and no eveidence of fuel...this plug was clean and dry?
and Fucawi and Frank, I got it like this...i am just digging into its issues...I have had it out 5-6 times. so only blame me from here forward....
I could pull the head to just end the guessing...ordered a second fm since the chrysler one is CRAP. where can I web order in a kit for head removal that comes with all the needed o rings and/or gaskets?

i see the lead out labelled tach on the wiring block, but that isnt the pulse I need? Will and automotive inductive tach sensor work off plug lead 1 just for testing?
and lastly the spark test...i have performed these many times on Harleys, but I saw no spark on all 4 of these weird plugs...so is the spark test done the same way...turn it over while the plug is grounded and watch for the arc?

Re: zero compression on cyl 3 on chrysler 115

Your making it harder than it really is. Ten minutes and the head is off.

There will be no hole in the piston, only damaged cylinder walls and unusable piston. If your lucky, a head gasket that is completely torched.

Putting the head back on and trying to run it wtih a damaged cyl. is only inviting disaster.

Asess the damage and come up with a plan. Welding on a piston is not part of the plan!

Re: zero compression on cyl 3 on chrysler 115

Your plugs are right. Are you asking about head gasket and o-rings? or a complete block seal kit? Either way you should be able to find them on this site. However, you only need the headgasket if you are just removing the head? Sometimes you will get lucky and not tear it up, if this is the case I often reuse them if they look ok (I'm cheap). The tach signal wire is white (or should be). Spark test is as you stated, important part is grounding plugs. Yes you should be able to see the spark from the plug as you crank.

Re: zero compression on cyl 3 on chrysler 115

These are suface discharge plugs ..you have the right ones ...take the head off and send a photo........

Re: zero compression on cyl 3 on chrysler 115

10 minute head job...no way...cool was making it tough then due to harley experiences with what comes off to get the heads off., I will track down a head gasket , is that all i need or are there spacers and orings in there.
Plug test...I doubted my grounding...will do again when the work starts....leaving the boat parked ....not taking it to the lake...on the last long weekend of the summer when the weather forecast is hot and sunny....you feeling my pain?
found a wiseco price sheet for a new piston...will check here and ebay too.

Re: zero compression on cyl 3 on chrysler 115

there is no head gasket listed for the 115? can another be subbed?

Re: zero compression on cyl 3 on chrysler 115

Likely one from a 120 in your year, but don't quote me on that.