77 Jarota Timing/Valve Shim/Carb setup

Just for reference, I haven't pulled the cams off yet, but here are the shim sizes that were installed upon the reassembly by Scott. Its going to be awhile before I get back to this.

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I thought this foundry mark? was interesting, stamped between cylinder 2&3 on the exhaust side. Anyone know what it means?

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So here we are, most of the summer logged by enjoying the great outdoors with the wife and kids, getting to this bike project with a few others that were running just didn't pop into priority. Until now!

The new shim sizes have been ordered, and regardless of what the markings on top of the buckets in that pic in a previous post declare, all are over the 2.0 size in order to make the 8&10 spec except for one which is the intake valve on the riders left.

Looking forward to getting the shims in and remeasuring the spec across all, and getting the rebuilt carbs dialed in shortly afterward.
 
If the cams have been raised by 0.2mm and the shims are still in the 2.00mm range, that head is on its very last legs.  I wouldn't even bother going any further with such base material... but rather write a quote for doing the job properly. ::)

If stock valves (possibly tipped as well?) are fitted, they will be seriously recessed.  Can't expect decent flow or power from a worn-out, knackered head.

piet
 
Good to know now, thanks Piet. And ratfarts, of course.

Here are some reference images of the valves and head.

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Do the valves and head look as bad as you thought? If so, double ratfarts, as this means I can I can rule out that I fucked up the shim calculations, which was obviously the alternative I am hoping for.
 
And a cracked all-alloy head to boot.

Your valves look to have been re-faced, and the seating face has been narrowed to re-enhance flow.  Fitting new valves might get you an additional 0.2-0.4mm shim thickness (if the present valves haven't been shortened!).  Custom valves can restore shim thicknesses to an acceptable level, but won't detract from the crappy valve seat configuration.  These heads are notorious for cracking and porosity, and especially for their putty-like properties regarding seat stability.  They do make a novel doorstop though...

Stick it together as best you can (don't expect more than average), enjoy it as long as it holds together (maybe 5-8000 miles before it requires further attention) and start feeding the piggy bank, looking out for a useable skulled head, as late and un-molested as possible.  Worn-out is no problem, but it should show no signs of cracking, warping or having been skimmed.  Expect to invest in new guides, valves and seats, but that will result in a head that will offer more than satisfactory performance for a very long time. 

piet
 
Phew! I thought you were going to say I botched up my shim calculations. That's a relief.  ;)

Off to the "Wanted" section I go. But on my way, single malt.
 
may do you a deal, that all alloy 78 head you have there is my favourite head to use on our race engines, is far from stuffed and very desirable to me
straightforward to repair plus we can modify the combustion chambers to whatever shape we wish to use

 
Well, since the bike had no issues when I rode it from Santa Fe to Tulsa hell bent to make a flight in 100 degree temperatures, and we had it running well sans some final carb jetting and now awaiting valve shimming, and due to this zoomed in photo of the area in question... as they say in sports, upon further review, I'm satisfied its not a crack.

not_a_crack.png


More to come after the shimming is finalized.

 
angonemoto said:
Well, since the bike had no issues when I rode it from Santa Fe to Tulsa hell bent to make a flight in 100 degree temperatures, and we had it running well sans some final carb jetting and now awaiting valve shimming, and due to this zoomed in photo of the area in question... as they say in sports, upon further review, I'm satisfied its not a crack.

More to come after the shimming is finalized.
Click to expand...

Sure, it will run... but very far from its potential.  Might even last for years to come, but you'll never experience what the engine is really capable of.  Seeing all those sharp edges around the valve seats sends a shudder down my spine, I'm quite certain that Reds re-worked heads look very, very different to what left the factory.  The all-alloy heads make that kinda "easy", at least far easier than re-working skulled heads.

This head will throw up issues that you wouldn't experience with a skulled head (OK, these have other issues, but nowhere near as serious).

Not sure how often each combustion chamber is shown, but I see at least  one other crack.

Personally, I refuse to work on them.  Potential warranty issues would financially kill me.

piet
 
That great reply by Red has made my day..weve got to get him over here! As mentioned before i gave up trying to get my 79 skull jota head sorted after throwing money at it, then bought another good looking head which turned out to have been  decked at an angle..then got an unused RGS head stood for 30 years in Slaters showroom display engine. Looking at the pics in Andy Wagner catelogue, do they have lots of good heads in reality..what cost? I dont need one but its the part that is surely the most crucial to be able to replace or repair as the years roll on.
 
angonemoto said:
I'm satisfied its not a crack.
Click to expand...

If that's not a crack then it must be something else. Possibly a fracture, fissure, break, split, breach, rupture, cleft ...  ;)

Very common to find cracks between valve seats on an alloy head, and not just with Laverdas. I've seen exactly the same thing on a Honda.

Looks like at least two of your combustion chambers have cracks between valves, and all 3 have cracks into the spark plug holes. Needs a lot of welding.
 
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