Topic: Been awhile / My #1 Cylinder keeps tapping spark plug

[JamesHeller]

I got new coils because 2/4 weren't firing and now 1 keeps hitting the plug after it runs awhile is there a suggestion on how to fix that cause i dont wanna get a new one and have it continue to do so pls and thank you in advance

[Old Scrambler]

Stock motor?..........are crush-washers on plugs?.............No spark likely due to bad caps rather than coils.

[desertrefugee]

Wonder if that cylinder might’ve stripped out somewhere along the line and the helicoil or timecert is allowing the plug to thread further into the hole…?

Just a random thought…

[Don R]

 What number are the spark plugs? Sounds to me like a parts guy gave you the wrong ones.

[JamesHeller]

Stock motor?..........are crush-washers on plugs?.............No spark likely due to bad caps rather than coils.

Yes stock motor and yes crush washer on plugs and it does give spark also

[JamesHeller]

What number are the spark plugs? Sounds to me like a parts guy gave you the wrong ones.

spark plugs part number is D8EA NGK

[JamesHeller]

Wonder if that cylinder might’ve stripped out somewhere along the line and the helicoil or timecert is allowing the plug to thread further into the hole…?

Just a random thought…

   Thats food for further thought havent had time to get down and dirty but those are high possibilities but not riding and its almost winter so gonna have to open it up thank you

[JamesHeller]

This is the plug i pulled was still giving a spark

[newday777]

This is the plug i pulled was still giving a spark

Something is amiss in your motor if it is "stock" as you say it is to hit just 1 plug to bend it that way and not hit the other plugs too.
Looking through your posts you have not given full information when you post a question nor have you given the bike's history.
Do you have the history of the bike?
Do you have the service manual for it?

[Phoenix]

Stupid suggestion.  Use two crush washers.

[BenelliSEI]

Most speed shops sell spark plug shim washers. They are used to orient the spark plug with the gap facing into the chamber. Buy a package and use the thinnest one under that plug.

[scottly]

What is the number on the spark plug?

[JamesHeller]

This is the plug i pulled was still giving a spark

Something is amiss in your motor if it is "stock" as you say it is to hit just 1 plug to bend it that way and not hit the other plugs too.
Looking through your posts you have not given full information when you post a question nor have you given the bike's history.
Do you have the history of the bike?
Do you have the service manual for it?

bikes history grandfather bought it in 02 and rode it 2-3yrs and then it sat in his garage because one carb was leaking i brought it a 1yr ago rebuilt carbs still no start  got em  balanced and tuned got it runnning needed new coils for sure might need even smaller adjustments but it runs and rides that is all the history i got bike sat for a good 15+ yrs. And i dont have a service manual

[JamesHeller]

Spark plugs are NGK D8EA

[2wheels]

Is the motor very noisy (clanking) when running?
If it is.  Sounds like a connecting rod bearing is bad.

Did you do an oil change?  maybe lots of metal in the oil?

[BenelliSEI]

Pull the oil filter. If you lost a rod bearing, there will be “bearing dust” in the folds of the paper….

[Don R]

 The service manuals are posted in the stickys at the top of sohc/4 Bikes. I have been known to print the section I'm working on and take it to the shop. The page numbers don't always match so check that.

[Don R]

 I have an 812 big bore motor that had the pistons in backwards.  They were notched for the spark plugs, is it possible the old plug had a washer on it that came out unnoticed? 

[JamesHeller]

Possibly but when i get some time gonna check because it doesn't knock at all and runs but eventually that plug gets tapped 

[bryanj]

Just to confirm it doesnt happen immediately and engine has to run for a while for it to happen?

[Don R]

 My old 383 chevy race engine had piston to plug issues and I had to index the plugs every time. Your problem might be knowing which way to turn it to miss whatever it's hitting.
 For a test you could use an extra plug gasket to get it out of the hole. The spacer washers come in silver, copper and brass colors to tell the thickness.
  A racer I knew had a problem engine, he straightened his ground strap, bent it over and cut it off making the gap between the side of the center electrode and the end of the ground strap. O [[[[ it that makes sense. it took some practice to get the gap right.  Look up side gap electrode, airplane engines also use surface gap plugs that spark between the edge of the plug body and the center electrode. I used those in jr Dragsters for a while.

[Don R]

 Look up surface gap plugs, NGK Quicksilver and side gap plugs. There, that's everything I know about spark plugs.

[HondaMan]

In the normal CB750 engine, it is almost 3mm between the piston crown and the sparkplug's ground electrode. In a 10.25:1 compression big-bore forged-piston engine it is 1.5mm distance with most of the pistons I have seen. With the (ancient and rare) Henry Abe 12:1 compression pistons it is less than 1mm distance, so over time the carbon buildup on those Henry pistons could conceivably touch the ground electrode.

All this presupposes, though, that the sparkplug's hole is stock. Like others said above, if someone drilled out the hole and tapped in a Keensert or similar thread repair device, it's possible the hole is set too deep. If it is that case, you'll have to find a shorter-reach sparkplug that matches those threads, in a heatrange (NGK) 8 or (ND) range 24 type.

Or, pull the head and fix it correctly...

[PeWe]

Pull head to investigate the status of head and pistons a good idea.
It might be higher CR pistons that hit the plugs that ned double washers. Take washers from old plugs.
If head has issues replace it.

There are heads on eBay. The old might need new guides and valves anyway.

[xhevi]

Or start with a boroscope through the spark plug hole to get a view inside the cylinder and compare to others.

Get one that also has a side camera since you want to look at all sides.

Hopefully that will give you an idea.

Here's what I found inside a cylinder. Fresh top end but the valve of the compression tool was loose and had fallen into the bore. Lucky I decided to take one last look inside before I started that engine.

[JamesHeller]

Just to confirm it doesnt happen immediately and engine has to run for a while for it to happen?

Yes doesnt happen even when idle only during ride at about 50mph but two crushwashers did the job

[JamesHeller]

Stupid suggestion.  Use two crush washers.

it worked thanks for suggestion

[JamesHeller]

Is the motor very noisy (clanking) when running?
If it is.  Sounds like a connecting rod bearing is bad.

Did you do an oil change?  maybe lots of metal in the oil?

no motor clanking at all and no metal in oil

[bryanj]

If you are sure of both those then get another head