Discussion
Calling all engine Gurus..........
Heart stopped yesterday, driving along all of a sudden I get this loud slapping noise, almosed like a belt slap. After checking engine bay all is good. So I start the engine again same noise , imediatly turning it off.
The engine is an AS 377 with 685 hp. Soooooo..... today I pulled the engine out and put it on a stand , first job, to take the tappet covers off. One of the rockers had snapped off on the con rod side , by the looks of it ,a clean sheer.
My question is what could the cause be and could a loose tappet cause this ???
What else should I check for ?????
Advice would be greatly appreciated on a very long sunday afternoon
Regards
Andrew
Heart stopped yesterday, driving along all of a sudden I get this loud slapping noise, almosed like a belt slap. After checking engine bay all is good. So I start the engine again same noise , imediatly turning it off.
The engine is an AS 377 with 685 hp. Soooooo..... today I pulled the engine out and put it on a stand , first job, to take the tappet covers off. One of the rockers had snapped off on the con rod side , by the looks of it ,a clean sheer.
My question is what could the cause be and could a loose tappet cause this ???
What else should I check for ?????
Advice would be greatly appreciated on a very long sunday afternoon
Regards
Andrew
So many possibilities it is hard to know where to start.
Steve
- Are there any imperfections in the material at the break?
- Are any of the pushrods bent?
- When the engine is turned over by hand until a valve is fully open is there still a gap between some of the coils of both the inner and outer valve springs? Do this for both inlet and exhaust valves.
Steve
If its the roller rocker body (stainless or ally casting) its not uncommon for them to fatigue. On a 685 377 you will have a pretty wild cam profile and appropriate higher rate springs to keep things under control at high RPM.
Its worth checking the cam followers too, occasionally they can fail and contribute to the failure you now have.
Other common things to check before rebuild are pushrods (straight), valve spring condition (any broken), rocker stud (bent or stretched) tops of valves for signs of mushrooming. Maybe even the valve timing chain/gears too.
If not already fitted you might consider including a rev kit in your rebuild. These do help to keep the lifters following the cam profile at higher RPM and avoid hammering of the valve train.
Or, you could just replace the broken part, set the valve clearances and hope for the best. (I wouldn't though)
Good luck.
Its worth checking the cam followers too, occasionally they can fail and contribute to the failure you now have.
Other common things to check before rebuild are pushrods (straight), valve spring condition (any broken), rocker stud (bent or stretched) tops of valves for signs of mushrooming. Maybe even the valve timing chain/gears too.
If not already fitted you might consider including a rev kit in your rebuild. These do help to keep the lifters following the cam profile at higher RPM and avoid hammering of the valve train.
Or, you could just replace the broken part, set the valve clearances and hope for the best. (I wouldn't though)
Good luck.
All has been said above..
they do fatigue over time..but
when ordering id order a complete set just for piece of mind and make sure you know which ones they are as you can get diffirent ratio rockers as well.
check for broken valve sprngs and bent push rods(roll along a flat surface) but ive always replaced rockers and pushrods as a set anyway..
if you have gone to the trouble of removing the engine , id check valves movement, cam timing etc etc while you are at it, but fatigue or broken spring more likely and if a few push rods are bent id be checking valve piston clearance as timing might have moved if you have slotted cams.
i presume you have solid lifters ?? because if the are hydraulic one might have gone solid....
and answering your other question, yes valve clearance can cause this, if you did not have any, the piston and valve would have touched and the pushrod will be bent and the rocker snaped... if you have miles too much the hammering action against the rocker can cause them to break as well and you will see wear in the top of the valve and rocker where they touch...
when did you last do the clearances because AS recommend clearances every 1000 miles on solid lifter engines??
Dom
they do fatigue over time..but
when ordering id order a complete set just for piece of mind and make sure you know which ones they are as you can get diffirent ratio rockers as well.
check for broken valve sprngs and bent push rods(roll along a flat surface) but ive always replaced rockers and pushrods as a set anyway..
if you have gone to the trouble of removing the engine , id check valves movement, cam timing etc etc while you are at it, but fatigue or broken spring more likely and if a few push rods are bent id be checking valve piston clearance as timing might have moved if you have slotted cams.
i presume you have solid lifters ?? because if the are hydraulic one might have gone solid....
and answering your other question, yes valve clearance can cause this, if you did not have any, the piston and valve would have touched and the pushrod will be bent and the rocker snaped... if you have miles too much the hammering action against the rocker can cause them to break as well and you will see wear in the top of the valve and rocker where they touch...
when did you last do the clearances because AS recommend clearances every 1000 miles on solid lifter engines??
Dom
Edited by V8Dom on Sunday 7th February 18:15
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