Knocking noise after spark plug change

[clay_wallace]

I've got a '95 Evinrude Intruder 175 and the other day it started running badly, seemed like it had fouled out a spark plug, so i called around and found some to replace them with. It had the champion QL78YC 's in it originally but all i could find around here were the NGk BPR7HS 's. I didnt have a gapper so i just put them in as they were. I then went and ran the boat and it ran great but it has a noise coming from the moter, like a knock or rattleing sound im really not sure. Could this be caused by the NGK's or possibly not being gapped right??? I know everyone says to run the champions but i didnt figure that it really mattered, Does it? The motor had no noise at all befor the spark plug changeout. PLease help

 

[hobiecat]

Re: Knocking noise after spark plug change

Did you get the plugs in good?

 

[clay_wallace]

Re: Knocking noise after spark plug change

Well i was reading other posts on here and saw that that might be a cause of some noise so went down earlier and made sure they were all good and tight, I prolly put another 1/8 of a turn or so on each one. Wont have a chance to check and see if that had any effect on it for a day or so, Anymore suggestions?

 

[dozerII]

Re: Knocking noise after spark plug change

According to some of the post on this forum, some people are of the opinion that running NGK's in a Johnyrude can cost you a motor. I would not chance it in mine and will always have a spare set.
Glen

 

[clay_wallace]

Re: Knocking noise after spark plug change

I know ive read those too, but none of them said anything about the NGK's causing a knock or noise of anykind. The only reason i didnt go with champions is because i couldnt find any.

 

[kbait]

Re: Knocking noise after spark plug change

Are the ngk's of longer reach? I bought a cheap 'lil johnny once that had too long of plugs in it and had no spark plug gap! Correct plugs corrected problem. If you charted the ngk plugs to the original champions, they should be fine. The 1/8 tighten won't matter. Gap gauge will.

 

[cajuncook1]

Re: Knocking noise after spark plug change

Are the ngk's of longer reach? I bought a cheap 'lil johnny once that had too long of plugs in it and had no spark plug gap! Correct plugs corrected problem. If you charted the ngk plugs to the original champions, they should be fine. The 1/8 tighten won't matter. Gap gauge will.

So, do you think the Ngk's are longer inside and the pistons might be tapping/hitting the end the spark plug??

cajuncook1

 

[CharlieB]

Re: Knocking noise after spark plug change

GENERALLY, the NGK has been known to cause RFI which the J/E Ignition module may 'sense' and may cause erratic ignition timing at upper RPM.

The Champion plugs use the correct inductance/resistance for the J/E ignition.

The B7 may be too hot of a plug. A B8hs is a closer match in heat range. BUT, it still can cause erratic timing at higher RPM.

Pull the NGK's out and inspect them very carefully, you are looking for any signs of overheating the spark plug tip which could cause it to act like a glow plug, pre-ignition could sound like your 'knocking' at higher RPM. Use a mirror and flash sunlight into the spark plug hole so that you can see the piston clearly. Normal appearance is a black sooted coating that can vary from almost dry, light black to an oily dark black. Hopefully you will not see a pitted moonscape of aluminum. If so immediately test compression and do not operate the motor until the correct Champion plugs are installed.

If you see ANY aluminum 'splatter' on the spark plugs that is a sure sign of pre-ignition/overheating doing damage to the pistons. DO NOT operate the motor if you find this.

Order the correct spark plugs.

 

[DJ]

Re: Knocking noise after spark plug change

Get those NGK's out of there-NOW.

I'm no fan of Champion but OMC engines loved them and I'm a believer when it comes to those OMC engines.

 

[JB]

Re: Knocking noise after spark plug change

What DJ said, and be sure they are correctly gapped. . ..030" to .040". . .with .030" preferred.

 

[Vic.S]

Re: Knocking noise after spark plug change

NGK BPR7HS are resistively suppressed (Denoted by "R")
You should not be using resistively supressed plugs. You should be using inductively suppressed plugs such as the QL78YC The "Q" in the Champion number denotes inductive suppression.

I cannot find an NGK equivalnet of QL78YC

Generally though "Z" in an NGK number denotes inductive suppression.

Its the resistive suppression that causes the RFI, and other, problems that has been mentioned

Explanation at http://members.iinet.net.au/~pauldawson/iame26-spark-plugs.PDF

 

[clay_wallace]

Re: Knocking noise after spark plug change

I realize that the NGK's are a bad idea, and i plan on changing them out for the champions tomorrow, but is there anyway that that could be the cause of my noise?? Its stressing me out bad, I dont want to have to take it somewhere this time of year...

 

[mark1961]

Re: Knocking noise after spark plug change

I realize that the NGK's are a bad idea, and i plan on changing them out for the champions tomorrow, but is there anyway that that could be the cause of my noise?? Its stressing me out bad, I dont want to have to take it somewhere this time of year...

Did you read CharlieB's post re pre ignition?