Export thread

Craftsman Mower 917.376240_REBUILT WONT START

#1

C

cjt28

Hello all, first time poster. Awhile back I decided to rebuild a mower that had “slop” in the piston ring when connected to the crankshaft. I was successful in getting it to run [ran like new!] but the spark plug blew out of the cylinder head because the threads were stripped from installing and uninstalling the spark plug. Instead of retapping the threads I went a cheaper route and bought a used cylinder head. I installed the cylinder head with new gasket and now the mower won’t start. I’m using a new spark plug. Rechecked the ignition coil on the flywheel with a feeler gauge. Also checked the ignition coil with my multimeter and got a reading of 5000 ohms. Any help would be appreciated.

Attachments





#2

Scrubcadet10

Scrubcadet10

What did you tighten the head bolts too?
Spec is 140 in lbs, I did that once and forgot to torque the head bolts and they were just tightened down with my nut driver, torqued to spec and it fires right up.
Seems kind of odd the threads blew out, might be an underlying issue, maybe not.


#3

C

cjt28

Re: Craftsman Mower 917.376240_REBUILT WONT STARt

Thanks I’ll try that tomorrow. I was torquing to 200 in lbs. Luckily, no bolts broke. Guess I was using the wrong guide. Threads blew because I tightened the plug to tight and kept screwing it in and unscrewing. Beginner here.

120000 Vertical Shaft
http://www4.briggsandstratton.com/mi...art_ms3992.pdf


#4

B

bertsmobile1

Don't go into hysterics about the numbers.
What is important is they are tight and all the same so there is no weak spot where the gasket can blow.
As you are confessed newbie triple check that you set the valve lash on the compression stroke & not the exhaust stroke.
Both valve should sit roughly parallel in the head.
If one looks a lot further down than the other then it is not on compression.
Worst come to worst you can always go get an insert fitted into the old head.
Get a solid one, not a helicoil or Recoil type wire one.
Most shops should be able to do it for you for around $ 25, as will most auto repair shops , boat shops etc.
Stock in trade for alloy heads but just make sure it is a solid one and from then on put a TOUCH of silver anti-sieze on the threads before you fit the plug.


#5

C

cjt28

Scrubcadet10 said:
What did you tighten the head bolts too?
Spec is 140 in lbs, I did that once and forgot to torque the head bolts and they were just tightened down with my nut driver, torqued to spec and it fires right up.
Seems kind of odd the threads blew out, might be an underlying issue, maybe not.
Click to expand...

Tried the above and the mower started, ran for a few secs. Now it won’t stay running.


#6

C

cjt28

bertsmobile1 said:
Don't go into hysterics about the numbers.
What is important is they are tight and all the same so there is no weak spot where the gasket can blow.
As you are confessed newbie triple check that you set the valve lash on the compression stroke & not the exhaust stroke.
Both valve should sit roughly parallel in the head.
If one looks a lot further down than the other then it is not on compression.
Worst come to worst you can always go get an insert fitted into the old head.
Get a solid one, not a helicoil or Recoil type wire one.
Most shops should be able to do it for you for around $ 25, as will most auto repair shops , boat shops etc.
Stock in trade for alloy heads but just make sure it is a solid one and from then on put a TOUCH of silver anti-sieze on the threads before you fit the plug.
Click to expand...

Not sure what you mean, can you upload a picture or diagram. I have no valve lashes to adjust on this mower.


#7

Scrubcadet10

Scrubcadet10

Valve lash A.K.A valve clearance, its the clearance between valve and tappet,
valve clearance for your engine is Intake valve (.005-.007) Exhaust (.007-.009) thats 5 thousandths to 7 thousandths intake, and 7 thousandths to 9 thousandths exhaust.
BUT, i believe on flat heads if the gap is too small, you have to grind the end of the valve, anyone confirm that?


#8

Scrubcadet10

Scrubcadet10

https://youtu.be/0w2BRxAiUKw?t=362


#9

R

Rivets

When you did the rebuild, did you have the tappets out? If you did you may have switched them around, which will change the valve clearance. You have an L-head engine, the Intake clearance should be .005”-.007” and the Exhaust clearance should be .007”-.009”.


#10

C

cjt28

I might have switched the tappets around unknowingly. I took the engine completely apart. Tell me if the engine will run with them in incorrectly? A failure could be the spark plug blowing out while the threads [in the spark plug hole] were stripped?


#11

R

Rivets

I doubt that it would have caused the spark plug to blow out. If you didn’t reset the valve clearances, that could be your problem, especially if you refaced the valves and cut the valve seats.


#12

C

cjt28

I didn’t do anything to the valve or seats but only clean them.


#13

R

Rivets

Have you checked the valve clearance on both valves?


#14

C

cjt28

Rivets said:
Have you checked the valve clearance on both valves?
Click to expand...

No I have not. I'm not sure on where to check for clearances inside the block? On top of the valves are tappets. Should I stick a feeler gauge between the tappet and plastic camshaft?


#15

Scrubcadet10

Scrubcadet10

Scrubcadet10 said:
https://youtu.be/0w2BRxAiUKw?t=362
Click to expand...

Watch this part of the video I linked too.


#16

C

cjt28

Scrubcadet10 said:
Watch this part of the video I linked too.
Click to expand...

Got it thanks.


Footer Links 1

Top