slant head was fun while it lasted...

fenderhole

fenderhole

New Member
so i got the slant head a little over a month ago and was very pleased with the performance gained. however, yesterday i was cruising the city streets when all of a sudden my spark plug blew out of the head. i hadn't touched it since i installed the head and new plug when i first got it so i figured that plug plug probably had backed out due to vibration. this was not the case, upon closer examination i found that when the plug blew it took all the threads with it... not just some of the threads but ALL of them. no, i did not over torque the plug and it had been working great for a while now. i can only come to two conclusions; the first being that i alone had a defective head and failure was eminent regardless. the second, that the slant head raises compression so much that the weak aluminum threads can't take the greatly increased cylinder pressure. so now i'm back to running my stock head again. since the new batch of slant heads are probably in the mail to many readers right now, i will be interested to find out if other members have this same problem in the future.

fenderhole
:-||
 
Hi have a 80cc slant head no problems with it looks like yours came defective, there are some kit to repair that threads you can check.
 
Maybe use a helicoil and a second head gasket? That may keep you going, but the second gasket might defeat the purpose of using a slant head. :D
 
i dont think i'm gonna try to fix it, its junk now. besides, its only $12. i will probably get a new one but i will wait to see what experiences other members have first.
 
Helicoils are phenomenally strong in many cases stronger than any of the original threads. They can hold quit well. I've used them on these kits before.
 
wow im surprised that happened to you, bought mine about the same time and no problems here... The only other thing i can think of is maybe the sparkplug was crossthreaded? When i first bought my porsche 914 someone had crossthreaded the sparkplug and i replaced it with a threaded insert and no problems after that. The threaded insert is steel so a little harder to crossthread ;)
 
My vote is along the lines of the hole being oversized, not threaded properly in the first place. I'm sure the compression ratio is higher, but we aren't talking 13:1 or something.

AND I agree, a threaded insert would now make it a "better than" head. Easy to do, especially since you'll have the head off.

ALSO - I don't think the new slant heads are in yet. At least I'm ignorant/unaware of their arrival in BC.
 
A: There is not even the slightest chance that compression will push a plug out...even a crappy aluminum casting will have a shear strength of 6,000-8,000PSI. Lead, pewter, would not let go under compression...not this engine, or a turbo-charged diesel for that matter.

B: The fact that the plug is at an angle has nothing to do with it. Actually a head with an angled plug does absolutely nothing for these engines other than offer clearance for tight frame installations.

The plug loosened up, and hammered repeatedly until the threads were gone.

Jim
 
By any chance did you get the number off the plug ? I'm asking as I'm wondering if somehow
the wrong plug was provided in the kit. The heat range is what I'm wondering about. If the
plug was cross threaded or under tightened it could have blown out anyway. (even if the plug
were right)

I've worked on VW rail buggies and have seen plugs blow out and even the helicoil that was used
to repair the plug bore later blow out. And yes in the past even VW has had some inferior
cylinder heads which were prone to cracking. (German engineering & quality not withstanding)
 
eDJ said:
I've worked on VW rail buggies and have seen plugs blow out and even the helicoil that was used
to repair the plug bore later blow out. And yes in the past even VW has had some inferior
cylinder heads which were prone to cracking. (German engineering & quality not withstanding)
Click to expand...


I'm big into vw idi diesels, which run at 23:1. cracked heads are very common BETWEEN THE VALVES, but not in the thread bosses.
 
Creative Engineering said:
A: There is not even the slightest chance that compression will push a plug out...even a crappy aluminum casting will have a shear strength of 6,000-8,000PSI. Lead, pewter, would not let go under compression...not this engine, or a turbo-charged diesel for that matter.
Click to expand...

Actully it can.. 1999-2001 5.4L Ford mod V8's are notorious for blowing plugs out of the cylinder heads. the casting is too thin there.. the fix from Ford is a special helicoil kit or the newer redesigned heads
 
I had a plug blow out of the head in my subaru. Wound in a helicoil and it is still running strong 15,000 miles later.
So yes, plugs blow out, and yes, helicoils do work very well.
 
if you visit a briggs and stratton dealer, they have or can get. helicoil repair kits ( there not common to blow out on B&S engines but lots get cross threaded ).. only drawback is the kit cost's about $15
 
Mine to!

fenderhole said:
so i got the slant head a little over a month ago and was very pleased with the performance gained. however, yesterday i was cruising the city streets when all of a sudden my spark plug blew out of the head. i hadn't touched it since i installed the head and new plug when i first got it so i figured that plug plug probably had backed out due to vibration. this was not the case, upon closer examination i found that when the plug blew it took all the threads with it... not just some of the threads but ALL of them. no, i did not over torque the plug and it had been working great for a while now. i can only come to two conclusions; the first being that i alone had a defective head and failure was eminent regardless. the second, that the slant head raises compression so much that the weak aluminum threads can't take the greatly increased cylinder pressure. so now i'm back to running my stock head again. since the new batch of slant heads are probably in the mail to many readers right now, i will be interested to find out if other members have this same problem in the future.

fenderhole
:-||
Click to expand...

Same story here it lasted about a month (48cc) though the plug (b6hs) didnt exactly come out i noticed a loss of power then noted oil all ova the head. i took the plug out to see all threads gone
http://i429.photobucket.com/albums/qq14/stv1jzgte/P8120036.jpg

stv
 
I gotta go with Jim here. There is no way compression alone can blow a plug out. When your riding at 4000 rpm for 15 minutes the piston compression hits the plug 60,000 times. The plug doesn't have to be very loose for it to hammer the threads out. Unless the plug was unscrewed 3-4 turns it would hammer all the threads out. I've heli-coiled old outboard heads when the electrolsis ruined the plug threads. It makes them better than new.
 
Got mine from zoom. Was perfectly plug and play for me. I had to lean out my carb a bit, but it was running a bit rich with the stock head anyway.
 
I just got my slant head from Zoom. Apparently this batch of slant heads was borked, since the first one I got was garbage. They sent me a second one for free...still pretty poor quality, but at least the plug forms a decent seal (a small amount of oily goo still gets out). I have noticed a minor increase in mid-range power. It might just be a placebo effect, though.
 
You must log in or register to reply here.
Back
Top