View Full Version : Blowing head gaskets
I have an 8 hp Briggs I/C on a Little Wonder blower. About 2 weeks ago I cranked up the rpm's just by adjusting where the cable mounts at the engine. A week later I blew a head gasket. Now about 4 days later I blow another. All 7 or 8 bolts seemed to loosen up some from the vibration (may not have torqued them down enough). Unit is 4 yrs old.
Question: would the rpm's possibly being too high blow a head gasket? Or would the second one have blown due to not enough torque on the bolts? Thanks for any help.
11-15-2001, 07:06 PM
Many blown head gaskets on these little engines are caused by overheating and/or improper cool down prior to shutting down.
Make sure the cooling fins and cooling fan are clean of debris. Make sure you Idle the engine for a couple of minutes after running it hard.
It is very possible the second one blew from the bolts being too loose.
Beg, borrow, or steal a torque wrench
11-15-2001, 09:00 PM
:blob3: you may want to put a small dab of thread lock on those bolts to help with the vib., cool down is very important.T
11-16-2001, 04:09 AM
Never use any sort of thread locker on any bolt that needs to be torqued! The thread locker will throw off the torque readings on the bolt being torqued. Additionally when you go to retorque the bolt a few hours later the thread locker will make the retorquing useless as it will definatetly show incorrect readings. A lack of retorqueing could very well be the reason the second head gasket blew.
The only time you should ever use anything on a torqued bolt is when instructed to do so by the service manual.
What I recommend is obtaining a new head gasket, tap the head gasket bolt holes and die the bolts to clean up the threads and then torque and retorque the head gasket bolts according to the factory recommendations. Also check the head to see if it warped.
If the problem persists I would turn the rpms back down to the factory maximum.
11-16-2001, 08:36 AM
if you over-revved it you probably caused the blown head gasket.
bring the rpm's back to spec, clean head bolt threads and holes, deck the head and block ( use a large file and make sure the surfaces are square), install a new head gasket, make sure all cooling fins are clean...
never use lock-tite on head bolts unless it's aluminum flange type (gasketless), then you would gel-seal gasket maker.
11-16-2001, 09:40 AM
As state above don't use a thread lock unless the repair manual says to. B&S head bolt do not use thread lock, also do not use a lubricant on torqued bolt as you will over torque the bolt(unless required as per a manual). Antiseeze compounds are about the only thing you would want to use on head bolts especially around the exhaust manifold.
If the head is warped this would be the reason you would be losing head gaskets also. Heads can be resurfaced on a thick piece of glass(min 3/8" thick) using a sheet of 220 grit silicon carbide sand paper. Normally I spray the sheet of sand paper with a lubricant like WD40 to help hold the sheet in place. If it is warped bad you can use a coarse grit dry to remove more material. With no lubricant, when the sheet is loaded with particles you can shake it off and reuse the sheet.
Sand the head one direction for so many strokes, then rotate 90 degrees and use the same number of strokes. Once you can see full contact of the gasket area with the sand paper use a figure 8 stroke to finish up with.
Use a torque wrench in a criss cross patern and recheck torque a second time in the same criss cross patern. You will normally find that the first 2 to 3 bolts will tighten down some more.
Engine high rpm should be set at or just below 3600rpm with no load. Since this is on a blower you will need to unload the engine. This is done by plugging the air intake to the blower. You will not feel any air flow when you have unloaded the engine. Once you set the high rpm in this manner, you not have any more problems with you head gasket. Note that at full throttle with the blower loading the engine it will not run at what you set the rpms at. If you adjust it to do so you will have engine failure in the near future.
11-17-2001, 05:22 PM
you most likely ran it too fast. my rider's 7 horse will die if you run it too fast.
11-17-2001, 07:51 PM
They run 5 hp briggs 6000 rpms when racing with a stock head gasket all day. As stated above your problem is in the torque and retourque of the head bolts. Check to see if the head and block are flat and clean. Also check to see if the cooling fins are clear. I'm mostly repeating most comments above. You can overheat the engine is you run too low rpm's while lugging it. Usually you should use engine oil on the threads and a little onder the bolt head. Most of the time I use anti-seize compound there. Good luck.
12-01-2001, 11:02 AM
first you should actually torque the bolts to spec.....if they fail to torque properly you should replace the head bolts as they can stretch.......good luck
01-27-2002, 01:40 PM
THAT IS AREAL GOOD WAY TO BUST OUT THE THREAD BOSSES ON CERTAIN AREAS ,.SILICON WILL DO THIS WORSE THAN ANYTHING , iSAW AN OLD HARLEY ONE TIME THAT A GUY HAD FORCED SILICON DOWN INTO THE THREAD BOSSES ON HIS PRIMARY COVER AND BUSTED EVERY ONE OF THEM :(
01-27-2002, 06:48 PM
I agree with you BigJames. If you fill the bores up with oil and put the bolt in then you may break the bore out. Also the guy who put silicone in the bore was probably trying to seal the bolt on a water cooled engine. This can also blow the bore out. On the small air cooled engines you should have a clean bolt and have ran a tap in the bores to make sure all is clean. Then blow out the bore and put a coat of engine oil on the bolt threads only. Then put a small amount under the bolt head. This is the correct way to do it with no problems. If working on a water cooled engine where the head bolts are wet (penitrating into the coolant) then clean as said and apply copper coat to the bolt threads only and a touch of anti-seeze under the head. If it is a dry bolt then treat it like it is an air cooled engine. When in doubt check your manual.
01-27-2002, 08:38 PM
After you replace the gasket again, try this.
After each heating/cooling cycle, re-torque the head bolts. Repeat until the bolts no longer turn when re-torquing.
01-27-2002, 08:50 PM
When retorquing loosen the bolt 1 turn before torquing. Also squirt a little oil under the bolt head. This will give you the best results. Once a head bolt has been torqued it is kind of set hard. It may take more torque to break it loose in tightening then the torque value. This will make you think that they don't need to be torqued - but it will fool you. So loosen a little and then retorque. Try marking a line on your bolt and head to show where the bolt is now. Then loosen and retorque. Note the difference. Then do the same on another bolt but this time don't loosen it. You will see a lot of difference.
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