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power loss / bit of noise

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prmac

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Hello all from the Great White North, the Canadian Northern Shore of Lake Huron. I've changed computers a couple times in the winter and lost this site on the way. The site looks a bit different so I hope I'm posting to the right place. The garage thermometer is back in the plusses(yea metric for above freezing the bullocks off the bull)and its time to figure out what happenned to my baby last fall. She's a '76 MGB which began making some unerving clattering noises and lost most of her power, though I could limp her the quarter mile home. I checked the valve clearances at the time and they were okay. I just pulled the head and two sets of valves are real clean and two sets are slightly burnt but the local mechanic says they arn't bad enough to cause the problem. The Head Gasket between two of the sets of valves, on the circle has burnt a space about a half an inch long. The mechanic suspects this but he won't commit himself and says take it to a expert. Of course in a town of ninety-two every one with a pint of bitter in his hand is an expert. I did take out the pushrods and one is a little bent. Is there such a thing as a Little bent? One of the blokes said this would cause the power loss, the noise and the heat to burn the gasket.
Since the head is off I'll take it into an engine shop a few towns down the road and have them check it for cracks and clean the valves. Meanwhile I'll order pushrods and a Head Gasket from the big city. Can I just chenge the bent one or do I have to replace them all?
And why I'm here; should this do the trick or do I have to delve deeper into the engine?
 
To paraphrase the late Sam Donaldson, hold on there Mr. prmac.

Did you do any diagnostics before you took the cylinder head off? Was it getting spark? Was it getting fuel? Did you do a compression or preferrably a cylinder leakdown test? Was their fuel or oil in the coolant? Was there coolant in the oil?

Hopefully you did these basics, but there is no indication you did, so that's why I'm asking.

How do you know your pushrod is bent? The test I've used is roll it on a piece of flat glass. Pushrods don't die, they're murdered.

If you have another straight one, you should be able to replace the bent one with that one.

As far as the head, was there any external leaking, however small, of coolant?

Have your person check the head for cracking and warping. Mine had a .004" warp in it before the rebuild.

Will this do the trick? Not enough information to tell.

Just don't want to see you throwing cubic dollars at this & not really fixing anything. Take it slow & logical.

Hope this helps. Let us know how you make out.

Colin
 
Clattering and bent pushrod may also indicate a sticking or stuck lifter, or a sticking vale stem. You need to pull lifters (first) and valves (second, if the lifter is ok) out and check them too. Use a light and check the cam lobes for wear, discoloration, or damage.
 
Colin, Unfortunately I didn't do the tests you listed. The car was running great when one morning I was going to the corner store and from the stop, she wouldn't get up to speed. As I turned around and put strain on the engine (my drive is uphill)the clettering started. The car would start but needed some tender throttling to keep her going. To all it seemed like a timing problem. Before taking the front end apart I thought I'd take it to the local mechanic. Timing was good, compression was down on two cylenders. He did a general look-about and figured it to be a valve or Head Gasket problem, which he didn't want to get involved with. I have to go away for a couple days but I will check the removed anti-freeze for oil and gas. I can drain the oil if that would help.
I rolled the push rods on a flat surface and one was slightly bent towards the lower end. The ends of the pushrod look good. I will check back in here when I get back and if there is no new news, I'll check the lifters and try to tackle the stems.
I do have one bit of idiocy to report, A week before the problem a friend's kid drove it and shifted from forth to second. The gear went in. I thought we were going to do a nose stand. I took it out for a good shakedown after that and it semed fine but...?
The other thing is the closest British car mechanic is two hours away. He's expensive and made some very strange suggestions, (I've had this car for seventeen years and have bever been told to bore the jets on my Webber before). The nxt best thing is Toronto,six hours away driving. The more I can do the better.
Get back to you Thursday.
Paul
 
Paul;
Where are you located at?
I'm in Tillsonburg, (north shore of Lake Erie, near Long Point)
I have been a mechanic for 40 years, give or take a millennium.
I'll help if I can.

Dave :savewave:
 
Hi Dave,
I'm in a small town called Serpent River; about half way between Sudbury and Sault Ste.Marie. My grandparents lived in Aylmer when they were alive so I know Tobacco Country a little. I'm kind of hoping I can get the girl on the road for the Ancaster British Flea Market next month. Do you go?

After I figured out Lifters were tappets (Hey, it's -27(-17 US) with wind chill here, my brains a little frozen)I went to the garage and realized it was just too damned cold to work out there today. I brought the pushrods in and rolled them on a sheet of glass. One is still ever so slightly bent. Tomorrow is cold again so I will probably take the side covers off Friday and look at the Lifters and the Cam lobes. There was no sign of foreign fluids in the drained Anti-freeze and the oil on the dip stick looks pure. The spark plugs are good.
Now I have to step back and mention something I can't belive I had forgotten until I looked in my parts tray. There was a strange copper object on the top of the head when I pulled off the valve cover, a small bullet shaped object 3/4 " long and 3/8 inch wide, with a rectangular back end (I assume for turning) It looks like a valve on a small hydraulic jack. It looks a bit bashed about. Looking in the Haynes manual it looks like it could be the locking screw for the rocker arm bracket though there are no signs of the lockplate, washer and nut. These are missing on the assembly.
Also the ball end of the adjusting screws for the rockers are worn with one being quite gashed.
I'll take all the parts to the engine shop to inspect.
Paul
 
Sounds like a valve problem to me going from 4th to 2nd may have bent the rod , gashed the adjuster and spit the other piece found loose off the rocker arm! You definitely would loose compression! :thirsty:
 
Well Paul;
You're more than a casual drive away from me.
I agree the downshift could have over revved the engine and made valves do strange things.

I am not sure about Ancaster this year as a couple of my days in April are booked. Have to check the schedule. If I go, I will look for you.
Good luck at the machine shop.

Dave :savewave:
 
If that part is the screw that locks the rocker shaft from turning and it came out i think the rocker assembly would go dry. Oil would take the path of least resistance and not be forced thru the shaft to lube the rocker bushes. Check for heavy scoring on the rocker shaft. Its not likly the shaft would have turned and stoped the oil from comming thru. They get pretty set when installed for lots of years! Let us know how you make out. Bob
 
prmac,

Reading your latest post then re-reading your original post jogged my rapidly fading memory. Your initial symptoms happened to me more than twenty years ago. Pretty much the same symptoms you described initialy. I had a rocker arm failure due to insufficent oiling. I had swapped out rocker arm assemblies, swapping out an offset oil passage one for the original straight oil passage, thus starving the rocker arm assembly of oil. When it failed it acted pretty much the same as yours did. I replaced it with a rebuilt assembly with a straight oil passage that matched the head & all was well.

Check your rocker arm assembly; you may see excessive wear on the shaft itself. Hope this helps.

Colin
 
prmac: find a tractor mechanic to work on the engine if the auto mechanic in town won't touch it. You could attempt to straighten the rod but new or used are not that expensive. I would also if getting into the guts of the engine want to investigate the timing chain under the front cover. Replacement chain AND tensioner is less than $25. A loose or worn chain could cause valve issues, or valve issue scould cause chain problems. Something in your engine decided to stop moving in proper direction. Also you need to look at piston tops to see if valves came in contact - one possible result would be a bent valve or two, which you can't really tell with them still in head.
 
You need to look elsewhere for a new pushrod...they're not that expensive.
 
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