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Discussion Starter #21
Hi All... Finally getting around to putting the 318 back together. I gave it a wash and it seems I created some corrosion on two of the cylinder head bolts sockets. I striped one of the bolts a little before stopping. My plan is to retap the block. I've honestly never used a tap&die set so this is a learning experience. Does anyone know what size of tap matches up to the 800-0571 onan bolt? I figure I only get one kick at the can before making things worse.


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Are you saying that you cross-threaded the bolt hole a little before you stopped? Was it a lot or did you catch it before you turned it in very far?

The key to running a tap is to use oil aND keep it perfectly straight and perpendicular to the hole. With existing threads, you should "feel" the tap want to follow the threads correctly and clean them up.

A lot of it is by feel...not easy to describe. It should NOT take a lot of twisting force to just clean up the threads.
 

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Also, you should be able to find the right tap by finding the correct die that matches up with the bolt threads. Many tap and die kits come with metal alligator-teeth looking gauges to check threads and tell you.
 

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Discussion Starter #24
Got about 1/4inch before making things worse. Seems like it's an 18 SAE thread type. Unfortunately the only two 18 taps are 1/4 and 3/8 in my new kit. The bolt is 3/8 (I think.. lol)


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Use that same gage to check your 1/4" tap. You should have a 1/4- 20 as the UNC version (Unified National Course). 1/4 - 28 would be UNF (Unified National Fine). The 3/8 tap should be 16 threads per inch, and marked as 3/8 - 16 UNC standard. The 5/16 - 18 UNC tap is what you want to match the bolt (capscrew) GMan mentioned. SAE tap sets will normally have a UNC and a UNF tap for each diameter.
If your tap set is marked differently, take 'em back!

Once you have the correct size and threads per inch tap, I'd recommend trying it in one of the undamaged holes first. A slight resistance can be felt as it cleans out the corrosion in the aluminum threads. The cutting part of the tap is tapered a bit, and will feel a little sloppy as you start it into a previously threaded hole. The full formed part of the tap actually does not cut. It smoothes the cut thread and assures the pitch is constant and uniform, and guides the cutting edges for straightness. The resistance will increase as it goes deeper or the corrosion is thicker. Give it a couple turns, then back out a half turn or so and continue until you reach the bottom where it gets tight very quickly! Don't try to force it.
Cutting a new thread in a properly drilled and sized hole requires much more torque even in aluminum. Steel requires even more power. The different grades and hardness of materials can be felt in all tapping operations, hand or machine. In hand tapping, many stops and backups to break the chips, will be the safest way to get a good thread and not break a tap off in the hole. That presents a real problem in the home shop.

tommyhawk
 

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Discussion Starter #27
Thanks tommyhawk & Gman!

I order the new bolt and finally found the time to put everything back together. The old 318 started up first try. I used to struggle a bit to get it going but now it turns over right away.

I started cutting the grass and ran into the same problem. The 318 struggles with the PTO on going up a hill or through long (not crazy long) grass. After 5-10mins it started to run rough so I parked it back in the garage. I was thinking maybe the bearings on the deck are seized causing the engine to work extra hard to spin them. But when I was backing up into the garage it still seemed to struggle without the PTO on. :dunno::dunno:
 

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I agree

Losing power warm does not sound like a head gasket to me.
I'd go with ignition system. Could be electronic ignition coil under the flywheel to just ignition coil if a P218G (you stated it was a 88 so it should be) or if a B43 if could be just need points & condenser.

Either way sounds heat related to ignition components.
 

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Discussion Starter #30
I'd go with ignition system. Could be electronic ignition coil under the flywheel to just ignition coil if a P218G (you stated it was a 88 so it should be) or if a B43 if could be just need points & condenser.

Either way sounds heat related to ignition components.
You are correct... I have the P218G. Never thought it could be the ignition coil since it seems to get spark and turn over.
 

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Discussion Starter #31
After some reading i'm now thinking the ignition control module might be the problem. I'm trying to test while the engine is still installed to verify.

I borrowed this pic from another thread where Chuckv shared it. I have a question though.... Should I be trying to crank the engine while doing this test or just put the key to "run"?
 

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Rob257 Adds,,

You are correct... I have the P218G. Never thought it could be the ignition coil since it seems to get spark and turn over.
A follow up. "ignition module" is inside the flywheel. Ignition coil is on top right side of the engine. See my thread just before your thread post, "318 Shuts Down".

Rob
 

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I also think it's the ignition module, someone else here is replacing one on a p series Onan.
 
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