Square four rebuild- next problem

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Gui.dorey
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Square four rebuild- next problem

Postby Gui.dorey » Mon Jan 21, 2019 10:22 pm

Hi everyone,

After my trouble with the valve guides, and milling them down with a help of my mate, I finally got everything assembled back together and now the engine turns and the valves all open and close as they should. However, while setting up the valve timing I came up with the next problem. This engine just leaves me baffled...

As I tried to set up the valve clearances, two of the valves had enough clearance to adjust, one had only 0.0008", another two about 0.0003 and the rest absolutely no gap. So basically most of the rockers are laying on the valves with no gap left to adjust.

One possible explanation I have is that the previous owner must have skimmed the head and barrel so much that the whole head is now much lower reducing the gaps to nil, if that is even possible. Another possibility is that my gasket between crankcase and barrel (found among all the parts) is too thin. The head gasket was an Otto, so the thickness would be correct. This barrel gasket was paper thin, and looking at Simon Hollyfield's pics in his blog, his looks much thicker.

So now I'm thinking about lifting the barrel and head back up, and replacing the barrel-crankcase gasket with a thicker one. Before that though, I'd like to hear your thoughts and ideas on this.

I did check that all the push rods are resting properly on the cam followers, and the valve timing worked perfectly following Bruce Longman's method.

Many thanks
Gui

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Re: Square four rebuild- next problem

Postby roger.fellows » Mon Jan 21, 2019 11:08 pm

Hello Gui, I'm not sure quite how to interpret what you say. When setting tappets you need to turn the engine to set each pair in turn. I'll look for the relevant scheme in the club info. Is that what you have tried or have you left the pistons in the same positions and tried to set all 8? You will probably find somewhere on the web a copper gasket which might solve your problem if there has been too much skimming.

Might be worth measuring barrel depth as near as you can. Are you getting any compression or are the plugs out anyway?

Excuse me if I'm asking silly questions!
Last edited by roger.fellows on Mon Jan 21, 2019 11:29 pm, edited 1 time in total.

roger.fellows
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Re: Square four rebuild- next problem

Postby roger.fellows » Mon Jan 21, 2019 11:11 pm

Might also be worth measuring the movement of each valve. Do you have any photos?

Answering an earlier point, the base gasket is a paper one as standard.
Last edited by roger.fellows on Tue Jan 22, 2019 12:00 am, edited 1 time in total.

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Re: Square four rebuild- next problem

Postby roger.fellows » Mon Jan 21, 2019 11:25 pm

What I've managed to find relates to an earlier engine, but the principle will be the same as the camshaft is common to all 1000 cc engines.

Rotate the engine until any inlet valve closes and then just past compression - much easier without plugs in and feeling just past TDC - and then set both valves for that cylinder.

I won't quote the gaps because you'll have those in Bruce's blurb.

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Re: Square four rebuild- next problem

Postby roger.fellows » Mon Jan 21, 2019 11:58 pm

I've been able to open another source. You are probably aware that the cylinders are numbered 1 2 3 4 starting front right and going clockwise.

The book says with No1 at TDC and both valves OPEN - held down by the rocker - set both valves for No3 cylinder - at .010" as a starting point.

Bring No2 to TDC with both valves open and set both valves on No4. Continue the sequence to set Nos 1 and 2.

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simon.holyfield
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Re: Square four rebuild- next problem

Postby simon.holyfield » Tue Jan 22, 2019 12:19 am

Gui,

Are you saying that there is no way to gain clearance by adjusting the rocker screws?

I'm wondering if your valves stems are longer than standard?
cheers

Simes

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

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Re: Square four rebuild- next problem

Postby roger.fellows » Tue Jan 22, 2019 12:46 am

Further to Simes' questions then: by how much do your valve tops stand proud of the top collars and what lengths are the compressed springs at greatest?

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Re: Square four rebuild- next problem

Postby Gui.dorey » Tue Jan 22, 2019 5:56 am

Roger, Simes,
I would have probably asked the same question you did, but of course I turned the engine for adjusting each rocker. Rule of nine and all that. The adjusting screws on the rockers are all the way out, and still I have no clearance to the valve stems.

When I had the issue with the guides I measured the length of the pushrods and they were correct. The valves are all new from Drags and also comparing to two old ones I had in the jumble of parts were also identical. While setting up the timing I clocked one valve and I got a travel of about 7.75mm. According to Longman's paper it should be more like 7.93mm but I attributed that to worn cams. I'll get some more measurements as you suggest, but I believe everything is correct. That's why I'm scratching my head at the moment...

Cheers
Gui

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simon.holyfield
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Re: Square four rebuild- next problem

Postby simon.holyfield » Tue Jan 22, 2019 7:20 am

Two thoughts then: cam base circle diameter, and the depth of the valve seat.

I think I have a picture of one of my combustion Chambers somewhere, I'll have a look for it.
cheers

Simes

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

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simon.holyfield
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Re: Square four rebuild- next problem

Postby simon.holyfield » Tue Jan 22, 2019 7:27 am

Have a look at this post:

http://ariel-square-four.blogspot.com/2 ... y.html?m=0

The valves are more or less level with the inside of the combustion chamber - no pocketing.
cheers

Simes

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


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