BBC engine help please

Got a 540 BBC. 14/71 30 over, merlin pro block, billet crank, venolia aluminium rods, 10.8 comp, blower pistons afr cnc heads, manton tappered pushrods, crane big lifters, new 340 on the seat springs, t and d shaft mounts. The engine has been together before and ran fine. has just been freshened with new rods pistons springs and valves. Took the car out for its first hit on the weekend. Sounded strong warming it up. In the burnout out reved it to about 6700 rpm and seemed fine. BAcked back and it sounded like it had fuelled a plug as I had it a little fat. Did my run on the 1/8th and it was flat but still running reasonbly ok. boost gauge was off the chart. Took it home and stripped. Numbers 2 6 8 cylinders the lifters are destroyed at the camshaft end both inlet and exhaust and are jammed in the bronze lifter bores, cam lobes seem in tact other than the marks, push rods dont seem bent and the rockers seem ok other than were the push rod has hit every were. some of the valves are bent. Cam timing seems good. Is set were it was previously. I need to find the problem before I order parts. All the lifter ends have smashed the bores, crank, rods and pistons. Any ideas please

 

Did you put new lifters in on your rebuild? Were the clearanced properly? Almost sounds like they were a little tight in the bores. How do the main and rod bearings look? If its just the lifters and not the bearings that could be something.

It could also be a valve float problem and you were smashing the lifters into the cam. 340lbs on the seat isn't huge spring pressure.

Can you put up some pictures?

 

Sounds to me like the valves hit pistons for whatever reason. Maybe the new rods and/or the new pistons are slightly different and you no longer have the valve to piston clearance you once had.

 

I just re-read everything and you said the lifter end smashed the bores,crank,rods and pistons?

I'm thinking possible piston to valve now also, BUT the rockers and the pushrods are not bent.

If the lifter seized in the bore, it would hang the valve open and when the piston cam up it would bend the valve, but you would think it would damage the pushrod also.

Corey

 

Is this a flat tappet cam or roller ? Where did you set the springs at ? What was your valve to piston clearance ?

 

Could have been coil binding also.

 

On our engines if we lean out a cylinder the valve will tulip which diminshes valve to piston clearance. If its bad enough they hit which always bends the valve and even if you can't see the lifters roller damage, it will show up in future runs. Now that I've experienced that, I just change them right away. But I have yet to bend a pushrod or a rocker arm (although I've ripped the intake port roof right out of the head)

 

Ripped the head apart? Wow. Seems anything is possible after reading that.

 

I was thinking piston to valve but i thought the push rods would be the first to bend. Its a billet roller cam. The lifters had done a couple of runs with that cam in the same lifter bores.

 

What size pushrods do you have? Manton pushrods are hard to bend

 

Not sure but they are big and taipered

 

Sounds like cam timing. Did you degree the cam after reassembly? could be timing set problem as well. Gear drive? Belt?? Check for excessive backlash in the cam drive. Under decellaration, the cam wants to "back up".

 

That happens when you beef up the springs, cam and don't buy the longer threaded studs to use all the threads in the cast aluminum heads---- you can't use the short studs that would work in cast iron heads -----------

 

Or in our case you have the expensive shaft rocker system (no studs) and yet you still don't use the supplied bolts because they could be deeper into the head on the exhaust side. Its a different story on the intake side as you basically screw right into the port roof. In the 2 times we've done this, both times the threads/bolts did not fail, it was the thin cross section from heavy porting that made it too weak and the fact that its the intake and its on cyl 7 or 2 (the intake is the last one so the shaft rocker bar system is cantilevered). We now have the head welded in and built up to reinforce it and of course try to make sure the exhaust doesn't have any issues, which causes the intake to open under higher than normal cyl psi.

 

Spent some more time investigating. Some of the exhaust valves are slightly bent. No marks on them or the piston but there bent. I gather thats enough to kill the lifters. So im next checkon cam timing. Had to hit for a reason im guessing

 

I agree with Comax Racing it sounds like valve float problem, especially with off the chart boost pressures ..... What rpm did it turn?? We have 490lbs spring seat pressure!!!!