Square Four Push Rods

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Gui.dorey
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Square Four Push Rods

Postby Gui.dorey » Fri Dec 28, 2018 3:43 pm

Hello everyone,

My engine rebuild is progressing along and I've assembled the head now. Today I assembled the rockers, but I must have done something wrong because the camshaft only turns a few degrees fwd and backwards and seems to get stuck, as if the valves hit something or reach the end of their travel.

Can it be that I have the wrong pushrods and they are too long? mine measure 5.787" or 147mm from bottom tip to the top edge of the cups. Could anyone please check if this is correct for a MkI?

TIA for any info or ideas,
Gui

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Re: Square Four Push Rods

Postby paul.ptak » Fri Dec 28, 2018 4:21 pm

I just measured one push rod with a cheap micrometer and see 145.96mm.

Paul

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Re: Square Four Push Rods

Postby MARK.WALSH » Fri Dec 28, 2018 5:15 pm

that's not good
Are you sure the engine is timed correctly and the cam is not hitting the pistons?
Also are you sure the bottom end of each pushrod is located in the relevant follower - it is possible for two push rods to be operated by one follower if not housed properly (easily done) - check by seeing if 2 adjacent rods move up or down at the same time. Easily rectified by slackening off the tappet adjuster and moving the pushrod over
Hope this helps
Kind regards
Mark

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paul.jameson
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Re: Square Four Push Rods

Postby paul.jameson » Fri Dec 28, 2018 8:50 pm

Did you fit the circlips to the cam followers? Especially if you omit these, a cam follower can turn slightly and then catch on the cam follower guide/holder in the cylinder. This gives exactly the symptom you describe.
Paul Jameson
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simon.holyfield
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Re: Square Four Push Rods

Postby simon.holyfield » Fri Dec 28, 2018 10:50 pm

You haven't got the push rods crossed in the tunnels have you?
cheers

Simes

'51 Square Four, '58 Huntmaster, '42 W/NG, http://ariel-square-four.blogspot.com

Gui.dorey
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Re: Square Four Push Rods

Postby Gui.dorey » Sat Dec 29, 2018 8:16 am

Hi everyone,
Thanks for the replies. I don't think I have the push rods crossed - I checked this thrice before assembling the rods and I do have the circlips on the followers. It seems as if the inlet valves for Nr 2 and Nr 4 are stuck or hitting something. I still haven't assembled the timing chain or done the timing, but I have all four pistons halfway down the stroke, so they are not hitting he pistons.

I will have to disassemble the rockers one after the other to check exactly what is going on.
Very strange...

Cheers
Gui

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Re: Square Four Push Rods

Postby nevhunter » Sat Dec 29, 2018 8:30 am

Just back off the adjustment at the moment . The valve guides might be too long at the top or your springs coil binding. Is the camshaft not rotating yet? Nev

Gui.dorey
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Re: Square Four Push Rods

Postby Gui.dorey » Sat Dec 29, 2018 11:06 am

Nothing worked, so I disassembled the rockers and found that the inlet valves of Nr 2 and 3 were stuck in their guides. So next the head came off again, and those two valves are definitely not moving for some reason, so will have to disassemble them as well.

All other valves are moving fine, although I have the feeling their travel is too short. Is that even possible? Guides, valves, springs etc are all new from drags, and at the moment I'm not sure what could be wrong or how I could have assembled something wrong.

Will keep you posted on the progress.
Gui

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Re: Square Four Push Rods

Postby john.whiting » Sat Dec 29, 2018 2:24 pm

It is possible to bend valve stems by use of a spring compressor.........unlikely,but I have seen it.......if the stems/ guides were free when the head was assembled,and the head hasnt sat for years,then its a puzzle..........As to your other issues...are the valve caps fouling the guides on full lift?...springs coil bound before full lift?.......I had a issue in a truck motor where the inner springs broke and got into the coils of the outers...a lot of noise,and bent pushrods and stems.

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Re: Square Four Push Rods

Postby Gui.dorey » Sat Dec 29, 2018 2:25 pm

I've got the valves all running freely in their guides now. There was a small burr on the top edge of the guides which was catching on the valve stems. My fault, when I drifted the new guides in and didn't check them properly after reaming.

However, I still think I have a problem. I still couldn't turn the camshaft completely with just the two front rockers assembled, so I measured the travel of my valves which is about 7mm until the spring collar hits the top of the valve guide. Measuring the travel of the push rods I get about 8mm. I have the later cams with ramps so I should get 7.94mm, but I just did a quick and dirty measuring without too much precision, so it sounds about right. This leaves me with 1mm difference between push rod travel and valve travel, so no wonder it wasn't working.

This leaves the question, why and what to do about it?
Are the parts from Drags wrong or not dimensioned properly?
I could try to take some material off the top of the guides or from the bottom of the valve collars - any of this sound well to you? Or will be doing more damage than good?
Does anyone know what the correct max travel for the valves actually is? I mean, when assembled with springs and so on, and one just pushes down on a valve - how much travel should one get?

I never worked on such a complicated engine before. Many moons ago I restored an 1954 Ariel NH and last year a 1930 BSA Sloper - all easy peasy compared to this beast, who I'm sure hates me for some reason. Will I ever get it running?

Cheers,
Gui


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