8n Conundrum

[Mark Lamb]

Please help me figure this out. Have search the internet but haven't found anything similar.

My '52 8n just started a knocking noise from what sounds like the top end. Here's what I've done since it started:

Oil change with 40 wt. and new filter.

Compression test. 100 on all four.

Oil pressure 25-35 while bushhogging
depending on height of grass

Yesterday was knocking at idle, under load and everthing in between. This morning, not nearly as bad at idle.

While experimenting, I started removing one plug wire at a time while running. Knocking ceases when wire removed from first plug from back. Resumes when wire is reconnected.

I don't see any evidence of manifold leak.

Any ideas? DELL, HOBO, anyone????

 

[Dell (WA)]

Mark.......summtimes mechanical KNOCKS are semi-difficult to precisely identify even with "stethoscopes" ...but... since it goes away with yer #1 sparkie, think about what is being "LOADED" with combustion pressure. ROD BEARING, eh???

While it could be pre-ignition knock from "leaded" sparkie gap, since you had to remove the sparkie to check the compression (100psi which is good) I would assume that you would also notice HEAVY deposits on yer sparkie gap. But for S&G's, replace yer sparkies ennyways. (this is cheaper than rebuilding yer engine to gitt ridd of rod knock) AutoLite 437's gapped 0.025" .......Dell

 

[Mark Lamb]

Thx Dell

Will give new plugs a try. I didn"t notice excess buildup on the 416 that was in there but like you said cheaper that rebuild.

Mark

 

[Jerry Kirkpatrick]

(quoted from post at 11:25:59 11/09/09) Please help me figure this out. Have search the internet but haven't found anything similar.

My '52 8n just started a knocking noise from what sounds like the top end. Here's what I've done since it started:

Oil change with 40 wt. and new filter.

Compression test. 100 on all four.

Oil pressure 25-35 while bushhogging
depending on height of grass

Yesterday was knocking at idle, under load and everthing in between. This morning, not nearly as bad at idle.

While experimenting, I started removing one plug wire at a time while running. Knocking ceases when wire removed from first plug from back. Resumes when wire is reconnected.

I don't see any evidence of manifold leak.

Any ideas? DELL, HOBO, anyone????

From personal experience, I would suggest you check that your distributor clamp screw hasn't come loose and allowed the distributor to move slightly and get your engine out of time...

JK

 

[Anonymous-0]

Before you go to major lengths to look at suspect bottom end stuff, might be worth a try to try this simple check: If'n she's been using any amount of oil, you may have carbon deposits on top of combustion chamber stuff. Wouldn't cost a dime to warm her up and spray a cupful of water into the carb intake at high idle. Might be surpirsed what comes out the exhaust.

Can't beat the price, if it works. If it doesn't, at least you are no poorer . . .

Good Luck. Let us know what you find.

 

[Mark Lamb]

Greybeard,

I want to make sure I understand you correctly. I should disconnect the hose from air cleaner to carb and spray (with a clean windex bottle?) apprx. 1 cup of water into the air intake of the carb.

I want to try it but want to do it right. Please let me know if I have it right. I assume this will help burn out any carbon buildup.

Thanks for your help.

 

[Mark Lamb]

Dell,

Tried a set of new Autolite 437's gapped to .025 to no avail. Might try Greybeard's suggestion of spraying water into carb intake in attempt to burn out any possible carbon residue. Do you concur?

Any other suggestions greatly appreciated!

Thx,
Mark L.

 

[Dell (WA)]

Mark.......I have no problem with Greybeard's suggestion of "steam-cleaning". Make certain yer engine is HOT and running at about 1/4-throttle. ......Dell

 

[Hobo,NC]

(quoted from post at 20:35:25 11/09/09) Before you go to major lengths to look at suspect bottom end stuff, might be worth a try to try this simple check: If'n she's been using any amount of oil, you may have carbon deposits on top of combustion chamber stuff. Wouldn't cost a dime to warm her up and spray a cupful of water into the carb intake at high idle. Might be surpirsed what comes out the exhaust.

Can't beat the price, if it works. If it doesn't, at least you are no poorer . . .

Good Luck. Let us know what you find.

simple enuff to do but it does not explain why the knock goes away when the combustion process is eliminated.

WARNING :!: all I know I read on the Internet,,, do it enuff and you can become a guru also,,, not responsible for damages,,, I read it and just pass it along,,, proceed with caution

 

[Ultradog MN]

Wrist pin maybe.
Did you try to put a long bar or stick to your ear to try to identify it further?
Personally I cringe at seeing these engines get torn down at the drop of a hat when it only needs a rod or piston or somesuch to get another 10 years of work out of it. If it is a piston you could probably find a used one pretty easy.
The thought of a bunch of China made internals in my old Ford makes the 100 compression numbers and used parts very attractive.

 

[Anonymous-0]

You have a bad connecting rod berring on that cyl.

 

[DavidO]

Yep! Hope is nice, but a bad rod bearing on that cylinder is most likely what is wrong.

 

[Terry Joe]

Mark, You may just have carbon built up on top of the pistons. Try top engine cleaner to try to remove carbon before tearing down. I had an engine knock on my 8n, and I decided to rebuild my engine, but found all my bearings to be ok. What I did find was carbon on top of the pistons knocking when it made contact with the head.

 

[Hobo,NC]

simple enuff to do but it does not explain why the knock goes away when the combustion process is eliminated.

WARNING :shock: all I know I read on the Internet,,, do it enuff and you can become a guru also,,, not responsible for damages,,, I read it and just pass it along,,, proceed with caution

 

[Dunk]

(quoted from post at 09:55:46 11/11/09)
simple enuff to do but it does not explain why the knock goes away when the combustion process is eliminated.

WARNING :shock: all I know I read on the Internet,,, do it enuff and you can become a guru also,,, not responsible for damages,,, I read it and just pass it along,,, proceed with caution

Did you say something, Hobo?

(I think you are right)

 

[Geo-TH,In]

(quoted from post at 17:25:59 11/09/09) Please help me figure this out. Have search the internet but haven't found anything similar.

My '52 8n just started a knocking noise from what sounds like the top end. Here's what I've done since it started:

Oil change with 40 wt. and new filter.

Compression test. 100 on all four.

Oil pressure 25-35 while bushhogging
depending on height of grass

Yesterday was knocking at idle, under load and everthing in between. This morning, not nearly as bad at idle.

While experimenting, I started removing one plug wire at a time while running. Knocking ceases when wire removed from first plug from back. Resumes when wire is reconnected.

I don't see any evidence of manifold leak.

Any ideas? DELL, HOBO, anyone????

Mark,
I have a 20 hp kohler on a Terramite T5C and kohler recommends to decarbon the top end every 500 hours. Kohler service rep discouraged using anything to decarbon the top end short of taking the head off and decarboning it manually. He said a large piece of carbon could get wedged between the piston and cylinder wall and do extensive damage. Some people recommend using Sea Foam. I went with the next hotter plug. I Would like to know if anyone has had engine damage using other methods like water or gas additives. IF not what is the best additive to keep old engines clean? I also have a Ford Jubilee and the plugs were black. Leaned the carburator out to a point that at an cold idle I have to choke it. Hope it keeps the plugs clean.
George