pushrods in series

[BillyShope]

I suppose this is a trivia question, but I was telling someone about the following and it bugged me that I couldn't remember the manufacturer responsible.

Some British engine manufacturer (Bristol?) used two pushrods to actuate the exhaust. The top pushrod was quite short and was positioned horizontally across the top of the engine between the two rockers. I saw a picture in a text as a student (or shortly thereafter) and saw one "in the flesh" at a car show in Orange, California about 20 years ago. Can someone jog my memory?

 

[kenre]

Could be wrong but didnt the Chrysler Hemi engine have a setup like you describe?

Ken

 

[BillyShope]

No, the Chrysler used a single pushrod for each valve, with long exhaust rockers to span the head.

I was coming back to this thread to tell everyone "never mind," for I found my answer after a little "googling."

http://www.boc.net/buyers_guide.html

The above will give the full history, for those who are interested. Seems I was right on the Bristol origins, but it was BMW that actually developed the aluminum hemi head with the "extra" pushrods. Bristol re-acquired the engine after the Second World War and ended up churing out 170 horses from two liters for their LeMans version. This was back in the fifties, so that's a pretty respectable figure.

 

[kenre]

Bristol re-acquired the engine after the Second World War and ended up churing out 170 horses from two liters for their LeMans version. This was back in the fifties, so that's a pretty respectable figure.

Have you looked up the BRM V16 used in formula one? Amazing engine. There is a soundfile that is downloadable, Would never thing it was only 1.5 litres!

 

[BillyShope]

Yes, Chrysler had a little book, in the engineering library, with clever transparent pages which allowed you to "tear down" the BRM engine as you turned the pages. Plus, there was a complete history of the engine and dyno figures.

(And, I meant to type "churning," not that it matters. No reason to allude to the making of butter, anyway.)

 

[Peter7307]

Billy,
Yep it was Bristol who used the two pushrods. The inlest were normally actauated by a single rod and rocjer arrangement.
The exhaust side was actuated by two rods...the ususal vertical rod puching on a crank to change the motion from vertical to almost horizontal and then a second , shorter rod encased in a tube operating the valve via a rocker arrangement.
The spark plugs were centrally located and the engine was a two litre in line six.
There is an excellent book by L J K Setright called Bristol Cars and Engines which gives a very thorough history of the engine development undertaken by Bristol on the engine which was originally built by BMW. Bristol acquired the rights to manufacture after WW II.
Bristol competed at Le Mans in 1953 , 4 and 5.
Check this site for more info on the engine:

http://www.boc.net/mo/library/401/autoeng.php

Carburettors were Solex downdraft type.

Cheers , Pete.

Cheers , Pete.

 

[BillyShope]

Thanks, Pete! I'm somewhat of a history buff.

According to what I've googled, BMW was responsible for the cylinder head. The engine was originally built by Bristol with a conventional valve train. That's why I said Bristol "re-acquired" the engine...with the BMW improvements...evidently as the fruits of war. But, I'm sure you know that, as it's undoubtedly covered in the book you mentioned.

 

[strokersix]

American Chevrolet 292 inline six engines have rather long pushrods at about 11 inches and only 5/16 inch diameter. Some engine builders install intermediate bushings and run two shorter pushrods in series. I presume the reason is to reduce buckling tendency of the long pushrods.

 

[BillyShope]

We're getting off subject, but that's fine with me.

Hadn't heard of that trick with the old "Stovebolt Six." (Had a friend, while an undergraduate, who cut one in half for installation in an MG. Don't know how far he got with the project. Recall, also, watching an SCCA airport race in Iowa City, in '54, where a '54 Corvette owner had surreptitiously replaced the 235 six with the larger truck block. Though starting behind a pack of XK's, he quickly passed them all, only to shell out the Powerglide when he accidentally put it in Park while downshifting.)

Slickest pushrod trick I've heard of is that which is used by Porsche. Specifically, they pack the hollow pushrods with "toothpicks." (Not really toothpicks, but you get the idea.)The wood is lighter than oil, but still allows oil flow.

 

[BillyShope]

Sorry, the 292 isn't in the same family as the old "Stovebolt Six." Wasn't thinking.

 

[BillyShope]

Just got an email from a friend who was involved in the design of the Chrysler 426 hemi. The "pushrods in series" solution was considered for the engine's exhaust valves, but the design never got past the layout stage. With a little tilting of the head, the exhaust rockers ended up no longer than those in the 392.

 

[Peter7307]

Renault used a straightforward and conventional arrangement for many years in the 16 TS where the pushrods were used to activate a single inlet and exhaust valve but allowed a hemispherical head layout with a central spark plug.
The engine was also used by Lotus foe the Europa in the 1960's before they adopted the "Twin Cam" based on the Ford.

Cheers , Pete.