• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

#5 Rocker Jumping off Pushrod

Share this page

tony barnhill

tony barnhill

Great Pumpkin - R.I.P
Offline
Okay, the latest in the saga of getting my '79 Vermillion Red MGB ready for the summer. Remember she blew her stack last week & scalded my stomach (https://www.britishcarforum.com/bcforum/ubbthreads.php/ubb/showflat/Number/287631/page/1#Post287631) & was running rough so I dinked around with the timing to get her smoothed out.

....Well, today, I replaced the original Opus distributor/coil & aftermarket Crane XR700 with a Pertronix distributor & Pertronix Flame Thrower coil (the Opus is notorious for failing - usually the amplifier assembly - & its been in there since the car was new) because I thought the indicators from our last drive (power loss) was possibly timing related (when I checked the timing with my light this afternoon, it was 3-degrees off - not bad for timing it by ear the other day!). I also wanted to head off possible problems if the Opus was going bad.....so, after setting the timing with the light, she ran like a bat out of...(you know where)..with that new ignition - impressive!

...except the tachometer didn't work...I can't remember but I think way back when I installed the Crane, I had to change a couple of tach wires; so, no big deal...

...then, while zipping down the road, she went "flutter"...then "POP, clack, bang" & lost all her power

So, I limped her back to the garage & pulled the valve cover...#5 rocker had jumped off the pushrod & lodged the pushrod between itself & the edge of the pushrod hole...so, I replaced the bent pushrod, retorqued the head & rocker assembly, & adjusted the valves....then, I took her for a drive....ran like a bat out of....

...then, while zipping down the road, she went "flutter"...then "POP, clack, bang" & lost all her power

I limped her back to the garageagain & pulled the valve cover one more time...the #5 rocker had jumped off the pushrod & lodged the pushrod between itself & the edge of the pushrod hole!

So, I've either got a bad tappet or worn cam!! & if the tappet's bad, you can bet the cam's worn!

She has 102,169 original miles on her & the engine's never been opened or pulled (I've done valve jobs & normal maintenance but nothing serious)....so, after I get back from Europe in July, its time to pull the engine & refresh it....oil pressure is about 60psi hot, 50 or so cold so it won't be major, just new rings, bearings, cam.
 
Tony, I had that problem in a pro 4cyl. racing engine and I had to have the bore for the lifter sleeved. You may want to check the fit of the lifter. Bob
 
May be a valve stem sticking in a guide and allowing the rod to come up and meet air, Tony. I'd be more inclined to look at that possibility. Some "upper cylinder lube" may be the cure...
and a period of less "spirited" piloting as the lube does its work... /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

Mebbe toss some Marvel in the crankcase?
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]You may want to check the fit of the lifter.[/QUOTE]

When I tear the engine down, I'll mic & magnaflux everything before putting it back together....I'm gonna strip an extra head tomorrow to take to the machine shop for new guides, valves, springs, etc.
 
/bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
 
If the cam was FUBAR I don't see the rod being bent, then all running well with a second one. It's in the head.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I don't see the rod being bent[/QUOTE]

Push rod, Doc...it was trapped between the rocker & the edge of its hole through the head....only slightly bent but when I rolled it over a smooth surface, I could see a little bend.
 
IF THE CAM WERE SHOT!!!

I read it, meant "pushrod" when I posted "rod" because you said so... and figure the valve is sticking in the guide allowing the rod to bounce around because the cam and lifter are fine... the rod WOULD get wedged where you found it if it were flappin' around with no rocker arm ball to hold it... when the valve got whacked back up by the piston or combustion shock, the rod would be out of position. The POP would be the mixture charge being ignited with the valve open.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]rod WOULD get wedged where you found it if it were flappin' around with no rocker arm ball to hold it... when the valve got whacked back up by the piston or combustion shock, the rod would be out of position. The POP would be the mixture charge being ignited with the valve open.[/QUOTE]

Interesting thought, Doc! The #5 valve opened & closed when I was adjusting the valves; but, you may be on to something.

I'm gonna go ahead & build a spare head I have on the shelf so I don't have to wait for the old one to be built....&, just for the heck of it, I'll pull the head before I yank the engine to sii if tghere's a bent valve in it.
 
I think you will find stem/guide problems, not a bent valve. Or more precisely: if the valve IS bent, it is as result of stem/guide problems to begin with.

Let it sit and do up another head. Swap 'em out and I bet your problem is solved.
 
Another thought: Does that head have the two spring setup or is it new enuff to have just one? My thought was: if the inner spring has fractured for some reason it would allow some odd valve "bounce" at higher RPM's due to less spring tension.
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Swap 'em out and I bet your problem is solved. [/QUOTE]

Think I'll try that - 60psi is still good oil pressure - & I really hate to pull the engine if it is in the head! If it is the lifter or cam all it'll do is bend another pushrod once the new head is on & I've got lots of them!

I can have the spare head stripped & magnafluxed in the time it takes for Moss to send me new guides & springs (along with seals)...plus, I might have to change a seat or 2 - won't know until the head's cleaned up & inspected.
 
My money's on the head as the problem area. Some bit o' crud got in the guide. Only other thing (and MUCH less likely) is a rocker seizing on the shaft from lack o' lube.
Change the head and DRIVE it some more! /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif
 
Well, guess who doesn't have an extra late head with the water port for the ZS carb? I've got every other head on the shelf except the one I need; can you believe that!.....so, I tossed a car cover over it. I'll pull my old head after I get back from Europe!
 
wow... that car must be going on strike this year or something!
 
Yeah, she's fighting me step by step...my '67 GT is now sitting in her spot next to a door & she's relegated to the middle row of cars in the garage...I'll let her think about things for a couple of months while the '67 gets to stretch its legs!
 
That will teach her! Better yet, why don't you set her outside...with the keys in her...maybe one of us will stop by and pull that head for you while you are away ;-)
 
Back
Top