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William Crowell
Samba Member
Joined: February 15, 2011
Posts: 70
Location: Placerville, CA
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 Posted: Thu Sep 17, 2020 12:29 pm Post subject: What caused Bus Grease Monkey's valves to tighten up? |
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Scott Crosby, diesel bus mechanic extraordinaire, recently had the engine on his Thing stop running because the valves tightened up after he carefully adjusted them with the engine cold:
https://www.youtube.com/watch?v=8Md_RnVv1kw&t=773s
I'm a 356 owner, and I am curious if you guys have any ideas about what might have caused this because it might apply to my vehicle. Thanks. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Thu Sep 17, 2020 1:04 pm Post subject: Re: What caused Bus Grease Monkey's valves to tighten up? |
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Well the things I see are he is checking the timing by turning the distributor, and not turning the crank. He needs to back the crank off 20° or so and then turn it passed the marks slowly and see where it fires. He could be way off doing it the way he is. It is of course better to set the timing at 28-32° BTDC at 4000+/- rpms, hoses off.
From the pictures of the lower distributor housing it looks to me like he has a problem with moisture in his oil.
The "U" bend in his breather hose is likely clogged with engine snot so he is going to have very poor crankcase ventilation if any. The hose needs to run as straight as possible so it can drain back into the crankcase after shutdown.
He might want to check for a rag or something clogging the intake to the cooling fan which would have cause his engine to run very hot. |
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William Crowell
Samba Member
Joined: February 15, 2011
Posts: 70
Location: Placerville, CA
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| Posted: Fri Sep 18, 2020 8:26 am Post subject: Re: What caused Bus Grease Monkey's valves to tighten up? |
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| The consensus seems to be that his engine experienced valve seat recession after the valves were adjusted, due to an extended highway drive at high speed on unleaded gas. I wonder why he did not have valve seat recession before that, though. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Fri Sep 18, 2020 1:50 pm Post subject: Re: What caused Bus Grease Monkey's valves to tighten up? |
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| William Crowell wrote: |
| The consensus seems to be that his engine experienced valve seat recession after the valves were adjusted, due to an extended highway drive at high speed on unleaded gas. I wonder why he did not have valve seat recession before that, though. |
What does unleaded gas have to do with this? Getting rid of leaded fuel has done more for extending engine life, including valve life than anything else that has happened during my lifetimes. |
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William Crowell
Samba Member
Joined: February 15, 2011
Posts: 70
Location: Placerville, CA
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| Posted: Fri Sep 18, 2020 2:41 pm Post subject: Re: What caused Bus Grease Monkey's valves to tighten up? |
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| When gas contained lead, valve seats didn't need to be hardened. With unleaded fuel, valve seats do need to be hardened. It's unclear whether Scott's cylinder heads had hardened seats. All Things are supposed to have them. |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50332
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| Posted: Fri Sep 18, 2020 3:57 pm Post subject: Re: What caused Bus Grease Monkey's valves to tighten up? |
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| William Crowell wrote: |
| When gas contained lead, valve seats didn't need to be hardened. With unleaded fuel, valve seats do need to be hardened. It's unclear whether Scott's cylinder heads had hardened seats. All Things are supposed to have them. |
Never owned a single automotive engine without hardened seats and many of them saw significantly significant mileage before leaded fuel was intoduced. What lead did do was build up on the seats and then flake off in an irregular manner allowing hot combustion gases to erode the seats. One vehicle I have owned since before lead was removed for the gas was notorious for burning valves, requiring a valve job every 20k miles or so. Once the lead was removed, on my rig at least I have never needed to do another valve job, just a light touch up at overhaul time.
Though I remember hearing this old mechanics tale many many times over the years, I don't think I ever saw any proof that it actually happened. I did see where lead damaged a lot of engines, whether it be valve and valve seats or clogging oil passages with heavy slug. Engines that ran high octane/high lead fuel were particularly vulnerable to being fouled with lead sludge. Modern high preformance-long life engines just wouldn't be possible is we still had leaded fuel. |
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