Jump to content

tubular or solid push rods


Recommended Posts

Hi googles a lot but cant find what the real advantages over a tubular push rod to a solid one  - less that the tubular ones cost a ton more.

Any help appreciated, pockets not so full presently but dont want to skimp during rebuild.  BTW, stock US74 engine, head is getting compression raised a bit, but not by a lot (skimmed a bit)

Thanks

Richard

 

Edited by AarhusTr6
Link to post
Share on other sites

 "advantages over a tubular push rod to a solid one"

Less weight, gives faster response and acceleration of engine components and ties in with reduced weight rockers, cam followers and valve caps. That's why carbon fibre pushrods have been tried, lighter and not supposed to bend, ...hmmm done some of them in. 

Mick Richards 

Edited by Motorsport Mickey
Link to post
Share on other sites

Hi Folks,

this may sound silly - I thought the standard rod was tubular.

Quite often solid rods are no stronger to bending as are tubular rods as the majority of the solid innards has no effect on supporting the bending.

I would have thought if you were going for lightness, strength and posh high expense it would be Titanium.

 

Roger

Link to post
Share on other sites
39 minutes ago, RogerH said:

Hi Folks,

this may sound silly - I thought the standard rod was tubular.

Quite often solid rods are no stronger to bending as are tubular rods as the majority of the solid innards has no effect on supporting the bending.

I would have thought if you were going for lightness, strength and posh high expense it would be Titanium.

 

Roger

+1 

Don't know anybody offering a Titanium pushrod and given the costs likely I'm sure unless I went back to racing I wouldn't want to buy them. As stated the carbon fibre pushrods used although promising gave me a couple of misfires which turned out to be bent pushrods which eventually jumped off the rocker fingers.

Mick Richards 

Link to post
Share on other sites

I would stick to steel rods, to differences in thermal expansion between block/head and push rods is minimized.

Waldi

Link to post
Share on other sites

For a basically standard engine, or even one mildly warmed over, is there any point? There's always somewhere to spend the money.

John

Link to post
Share on other sites

Richard,

If you are taking 170 thou off the head like we do when racing (unlikely on a 6 cylinder) then consider shorter push rods, if only - 30thou- 60 thou forget it. Not enough removed to make any difference, that's not just my opinion....

Mick Richards

 

Pushrods for milled heads

I don't know if anyone else has contributed their wisdom on pushrod length, but here is my understanding of it.

Theoretically, at half lift, the valve tip, the center line of the rocker shaft, and the pushrod end should be in a straight line.

So looking at the rocker position, one end at a time............

The alignment of the valve stem and the rocker shaft are determined by the valve stem length, the depth of machining for the valve seat, and the height of the rocker stands. The alignment is achieved by making the rocker stands taller or shorter. (Note -- with roller rockers, it is proper to have the centerline of the roller horizontal to the rocker shaft centerline, rather than having the contact line of the roller in line with it).

At the pushrod end of the rocker, this means that the centerline of the ball should be aligned with the centerline of the rocker shaft.

Pushrod length has no effect on alignment on the valve side of the rocker. The length of the pushrod depends on how much has been taken off the head and how much has been taken off the cam base circle by the regrinding. To make it theoretically correct, you must assemble the engine, position the valve halfway down, and measure the length required for the pushrod. This is done with an adjustable pushrod. At the valve end, the spring is replaced by a very light one to make the operation easy.

In real life, some builders go to all this trouble to measure the pushrod length, but many do not. Many just look at whether or not the adjusting screw is reasonably centered in the rocker, so that there is enough for the adjusting nut on the top and no interference of the pushrod on the bottom. Interestingly, it is often the case that about the same amount is milled off the head and is ground off the camshaft base circle, in which case, a stock length pushrod is just fine.

Jack Drews.

 

Jack's got it. And, that's the name of that tune.

Kas Kastner

 

Link to post
Share on other sites

I have used tubular pushrods on 6 cylinder engines . Probably not a "performance enhancer" on our engines with their rev range .they are usually recommended for their stiffness in high revving uses. However if they are to be used with the current crop of newly supplied rockers, Beware.  due to their different geometry compared with original Stanpart items, the larger diameter of the tubular pushrods may come into contact with the head casting. Best to check closely.

P

Link to post
Share on other sites

Paul,

The standard pushrods are tubular (they are) and if used with a rocker at the standard ratio the vertical motion will be in the same plane, how then can the pushrods come in contact with the head casting ? Are you saying the " current crop of newly supplied rockers " are not as per original spec ?

Mick Richards

Link to post
Share on other sites

Thanks George, ...understand now.

Mick Richards

Link to post
Share on other sites

Regards pushrod length, when I rebuilt my ex-US engine, I retained the original pushrods, after cleaning them up with a knotted wheel to get them nice and shiny again. US-spec head (3.535in deck height) was replaced with a UK head (3.400in deck height) and the standard pushrods still fitted. Had no problems in 6000 miles.
Also, when I replaced the 2-litre engine in my saloon with a 2500TC engine, head was skimmed down from 3.475in to 3.430in, and again the standard pushrods were retained. No issues after 50,000+ miles. Just my personal experience.

Matt

Link to post
Share on other sites
27 minutes ago, matt george said:

Regards pushrod length, when I rebuilt my ex-US engine, I retained the original pushrods, after cleaning them up with a knotted wheel to get them nice and shiny again. US-spec head (3.535in deck height) was replaced with a UK head (3.400in deck height) and the standard pushrods still fitted. Had no problems in 6000 miles.
Also, when I replaced the 2-litre engine in my saloon with a 2500TC engine, head was skimmed down from 3.475in to 3.430in, and again the standard pushrods were retained. No issues after 50,000+ miles. Just my personal experience.

Matt

Now that is strange, when I did mine some 20 years ago I couldn't get the tappets to adjust enough to use the US push rods so used UK ones. I can't remember how much came off the head but it is 9.5:1 cr so not to dramatic 

I suppose it could be differences in cam followers or the heel of cams

George 

Link to post
Share on other sites
1 hour ago, matt george said:

Regards pushrod length, when I rebuilt my ex-US engine, I retained the original pushrods, after cleaning them up with a knotted wheel to get them nice and shiny again. US-spec head (3.535in deck height) was replaced with a UK head (3.400in deck height) and the standard pushrods still fitted. Had no problems in 6000 miles.
Also, when I replaced the 2-litre engine in my saloon with a 2500TC engine, head was skimmed down from 3.475in to 3.430in, and again the standard pushrods were retained. No issues after 50,000+ miles. Just my personal experience.

Matt

Thanks Mat

Peter Burgess suggested getting short pushrods, but i will keep my old ones as well.

I see you are in Peterborough . . I am also originally from there, grew up in Ravensthrope, then Army, now Engineer in WindPower Denmark - so greetings to the old town which I have not been able to visit for ages . . :-(

Link to post
Share on other sites
1 hour ago, AarhusTr6 said:

Thanks Mat

Peter Burgess suggested getting short pushrods, but i will keep my old ones as well.

I see you are in Peterborough . . I am also originally from there, grew up in Ravensthrope, then Army, now Engineer in WindPower Denmark - so greetings to the old town which I have not been able to visit for ages . . :-(

This thread has become very local,  I am also close to Peterborough, little place called Pidley.

Mat do you go along to the Cambfollowers? (When we can go out to play)

George 

Edited by harlequin
Link to post
Share on other sites

Mick.

The standard pushrods I have used are 1/4 inch diameter and solid. (just to check I have just hacksawed an old one)

The rocker geometry of the pattern rockers I have previously obtained is not as the original Stanpart ones I have. The rocker ratio is slightly greater on the pattern copies (this can be seen from comparing the distance from the push rod connection to the rocker centreline) also the offset of the arms is different. The cam followers in the block seem to be set at a nominal 2" centres. With the standard rocker set up the Stanpart rocker pushrod adjusters are spaced at the same 2". With pattern rockers this is 1.875". the difference is not noticeable, unless the greater diameter tubular pushrods are used, when the pushrods can foul the head casting. (hence my previous post)

It would be interesting to learn why the pattern parts are not identical to the originals.

 

Paul

 

Link to post
Share on other sites

Tubular pushrods are an option on tuned high reving engines but do not do any harm on standard engines.

When properly done they are lighter than massive ones and do not bend. Bending at high revs may destroy

normal pushrods. They look like a banana after that. Lighter pushrods allow less spring force what helps to

increase cam life.

 

TR4 had tubular pushrods, TR6 has massive ones.

 

Interestingly pretty seldom it is taken into account that the rocker gallery must be lowered with high lift cams and from that

often shorter pushrods are needed than the 206mm from the CP PI. In that case tubular rods are a good choice, too.

they can be shortened to any length.

Link to post
Share on other sites
2 hours ago, harlequin said:

This thread has become very local,  I am also close to Peterborough, little place called Pidley.

Mat do you go along to the Cambfollowers? (When we can go out to play)

George 

George,

Funny you should say that, as we are actually in Ramsey, so I know Pidley reasonably well, too. Been through there plenty of times on my way to TRGB. I used to go to the Camb Followers meets sporadically years ago, but to the Millstone in Barnack. I believe that meet has gone, particularly as the pub is now shut and its very existence yet to be decided.
The car went back on the road in 2019 and I always meant to get to the CF meeting in Warboys as it's just down the road, but haven't made it as yet. Current situation not exactly helping, of course.

Matt

Link to post
Share on other sites

A bit late to the conversation, but for those shaving the head of a North American market car, the factory pushrods on these cars are longer than the ones that came on the PI cars.   Shaving down the head on a NA car to the 3.4 thickness of a PI head (to get a 9.5 to 1 compression) will normally require swapping in the PI length (shorter) pushrods.  Some folks do not do this and while they all do not have problems there are those who then check in after a bit with valve train issues related to geometry, rockers slipping off the pushrod etc.  

Link to post
Share on other sites

Mat

Wistow was the venue upto a couple of years ago, Cambfollowers then moved to Warboys when the 3 Horseshoes closed, it was going to be turned into a house but the locals got it blocked and it has reopened so we are back, I did hear that the Milstone is also going to reopen so that may become the location of the 2nd of the 2 monthly meetings 

George

Apologies for the waylaying of the thread

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.