Boom!

Moderators: Amskeptic, Sluggo

Post Reply
appetite
Getting Hooked!
Status: Offline

Boom!

Post by appetite » Thu Oct 05, 2017 7:42 pm

Boom! Went the bus as I accelerated out of a driveway this evening. WTF!?!

Immediate loss of power. Clattering in the engine compartment. Shut off the engine. Rainy and dark. Two hungry kids in the back.

I pull into a bank parking lot and start inspecting. Lo and behold, the #1 spark plug has blown out of its hole. I had no tools on hand, so i started the bus back up and limped back home on 3 cylinders.

What would make the plug blow out? Should I simply put the plug back in once the engine is cool or is there some diagnostic work to be done?

Thanks,

James

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Boom!

Post by Amskeptic » Fri Oct 06, 2017 8:59 am

appetite wrote:
Thu Oct 05, 2017 7:42 pm
Boom! Went the bus as I accelerated out of a driveway this evening. WTF!?!

Immediate loss of power. Clattering in the engine compartment. Shut off the engine. Rainy and dark. Two hungry kids in the back.

I pull into a bank parking lot and start inspecting. Lo and behold, the #1 spark plug has blown out of its hole. I had no tools on hand, so i started the bus back up and limped back home on 3 cylinders.

What would make the plug blow out? Should I simply put the plug back in once the engine is cool or is there some diagnostic work to be done?

Thanks,

James

Yikes.
1) Immediately check all other plugs for looseness. You need this information as forensics.
IF YES they are all loose, then #1 just got ahead of the others and fell out. You can expect that the last hole threads are damaged. Grease a fresh plug on the threads and carefully get it started and seat it. Carefully "tighten" but be very alert to a loss of force as you tighten. That would mean it is stripping.
If you cannot get a plug started in the hole, don't keep fiddling. It will need to be carefully "dressed" with a grease laden 14mm spark plug chaser - this is advanced mechanics and the consequences are severe.

IF NO, all other plugs are tight, then you might be hosed here. Do the above and finesse a plug into the hole with plenty of grease and barely bring it to snug. Remove plug. Do you see aluminum shards? Wipe off thoroughly and re-grease, re-install, carefully find the snug spot and check again. Wipe off grease. Re-install plug. Only tighten to noticeably more effort than hand tightening. Now try to tighten to snuggish and be very alert to a possible release of force. Stop if you feel it relax under your hand.

Bentley recommends 22 ft/lbs with new plugs, but we all go to snug with a little extra bunt.

If you pull this off, check plug every morning after you drive it the day before. If it holds, well, good luck. If it loosens considerably or never tightens at all, pull engine, pull tins, install either a timesert or plug helicoil under clean well-lit conditions, or pull head and have repaired.
Yikes,
Colin
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 112,220 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

appetite
Getting Hooked!
Status: Offline

Re: Boom!

Post by appetite » Fri Oct 06, 2017 11:13 am

Aw jeez.

OK, I will try all of the above.

appetite
Getting Hooked!
Status: Offline

Re: Boom!

Post by appetite » Fri Oct 06, 2017 1:48 pm

Forensic analysis:

#2 was pretty loose (I could unscrew it with my fingers)
#4 was snug
#3 was snug

I tightened #2.

For #1, the plug that blew out was chewed up a little bit at the end of the threads. I got a new plug, gapped it, put a dab of oil from the dipstick on the threads and hand tightened. It went in easily, without resistance. I unscrewed it, checked for shards and found none. I tightened and snugged the plug. Started up with a billow of white smoke, which dissipated after a few minutes. I went for a test drive.

The bus ran well, with a noticeable improvement in what I thought had been a low idle over the past week. Perhaps the bus was simply firing weakly and erratically because of the loose plugs?

Tomorrow, in the morning, with the engine cold, I will check for snugness on #1 and #2.

Question: why would #1 and #2 become loose in the first place?

Thanks,

James

User avatar
Amskeptic
IAC "Help Desk"
IAC "Help Desk"
Status: Offline

Re: Boom!

Post by Amskeptic » Sat Oct 07, 2017 4:48 am

appetite wrote:
Fri Oct 06, 2017 1:48 pm
#2 was pretty loose

I got a new plug, gapped it, put a dab of oil from the dipstick on the threads and hand tightened. It went in easily, without resistance. I unscrewed it, checked for shards and found none.


That's because you did not use grease. Grease adheres the aluminum shards to itself, oil just lets it slipslide into the combustion chamber as the plug screws in.

appetite wrote: Question: why would #1 and #2 become loose in the first place?
All plugs will develop a "set" through several heat/cool cycles. This can loosen your initial tightening torque.
Sure am glad #2 was loose too. Good job, kids must be really hungry now.
Colin
BobD - 1978 Bus . . . . . . . . . . . 112,660 miles
Chloe - 1970 bus . . . . . . . . . . . 206,820 miles
Naranja - 1977 Westfalia . . . . . 112,220 miles
Pluck - 1973 Squareback . . . . . . 55,570 miles
Alexus - 1991 Lexus LS400 . . . 78,885 miles

Post Reply