Rebuilding top end with copper gaskets n stuff...

So, two good things today... first, the weather is beautiful, contrary to miserable forecast. And second, the test ride was perfect, contrary to yesterday’s miserable show!

The bike is +.060” which makes it 774cc, I very much doubt that piston manufacturers change the dome to compensate for over size bores, so given they’re 8.6:1 pistons, I’d estimate mine has to be around 9:1.

Especially now, with the copper head gasket and removing the barrel base gasket I’ve taken around .030” out of the deck height. This alone would raise the CR close to half a point, but more importantly it tightens up the squish.

On the test ride today the most immediate noticeable difference was the almost total absence of pinking, this bike would easily pink before. How much of this is down to the cleaned up carbon and how much to the squish I don’t know.

Next noticeable difference was a more immediate and stronger initial acceleration and a definite improvement below 3,500rpm. Also stronger in the 4,000 to 5,500. I put this improvement down mainly to the functioning squish band.

Order has been returned to the shed. For now...
 
Fast Eddie said:
Not really. Lost on me mate !

If you’re talking female singers from that era it’s Blondie. Full stop. End of. No debate.
Click to expand...

Agree about Blondie and not really a fan of Toyah but she did a song called It's a Mystery:)

It's a mystery, it's a mystery
I'm still searching for a clue
It's a mystery to me
shot in the dark
The big question mark in history
Is it a mystery to you?

Glad you have sorted it though.
 
This is a great thread!! I had a leak from the pushrod seal and a blown headgasket (copper) over a year ago. Odd thing is, the bike still ran great. Did have an oil leak from the PR seals. All good now. That's a lot of carbon. That I didn't have. Not even discoloration. Difference on gas or oils in the UK and US?? They do hype the detergents around here.
 
Britfan60 said:
This is a great thread!! I had a leak from the pushrod seal and a blown headgasket (copper) over a year ago. Odd thing is, the bike still ran great. Did have an oil leak from the PR seals. All good now. That's a lot of carbon. That I didn't have. Not even discoloration. Difference on gas or oils in the UK and US?? They do hype the detergents around here.
Click to expand...

Quite straightforward really, it was burning oil like a freakin’ two stroke!

Oil was making its way down the front rocker box through studs and into the combustion chamber due to the gaskets not sealing. Thats where the carbon came from.
 
I've run in to a similar issue. Though oil consumption not terribly bad, definite fouling on the timing side. Pulled the head and barrels, the TS exhaust valve was very tight in the guide. So I've embarked on a top end rebuild. Inlet valves show obvious signs of leakage, so I think I'll go with inlet stem seals from Kibblewhite this time around.

IMG_3421.JPG


Followers appear to be in good shape, as are the cam lobes, these are R radius lifters matched to a T120 exhaust cam. Still deciding if I should replace the follower blocks, there's no perceptible play in the tappet bore, but I haven't measured them yet. The bronze tappet blocks from KPM are the bee's knees apparently

IMG_3423.JPG


Anyway, I won't hijack your thread Eddie, will start a new one
 
If it wasn’t over-revved, the valve must have got sticky in the guide.

Like yourself, I’ve always seen those caps as four extra chances to break down.
 
Triton Thrasher said:
If it wasn’t over-revved, the valve must have got sticky in the guide.

Like yourself, I’ve always seen those caps as four extra chances to break down.
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I can’t argue with your logic, but then again I can’t think why that shudda happened.

I’ve been wondering if the fouling of the copper rocker box base gasket and the missing cap are linked... maybe the fouling got tight, and momentarily held the pushrod before it freed off with a jolt, a jolt big enough to dislodge the cap?

We‘re shootin’ in the dark though.
 
Fast Eddie said:
I can’t argue with your logic, but then again I can’t think why that shudda happened.

I’ve been wondering if the fouling of the copper rocker box base gasket and the missing cap are linked... maybe the fouling got tight, and momentarily held the pushrod before it freed off with a jolt, a jolt big enough to dislodge the cap?

We‘re shootin’ in the dark though.
Click to expand...

They say it’s easy to be wise after the event, but I find it even easier to still not know, after the event.
 
I rarely get it up past 6k. Its old. Odd thing though when we changed the pushrod seals....found the copper head gasket with a nice scorched rip through it and it hadn't affected the running at all. I'm surprised I didn't break down.
 
Britfan60 said:
I rarely get it up past 6k. Its old. Odd thing though when we changed the pushrod seals....found the copper head gasket with a nice scorched rip through it and it hadn't affected the running at all. I'm surprised I didn't break down.
Click to expand...

Thats one of the benefits of a copper head gasket, they are less likely to blow out altogether and leave you stranded if / when they do fail, unlike composite.
 
xbacksideslider said:
Head steady can cause rocker box gasket crush when chassis is torqued by road loads.
Click to expand...

An interesting thought. Although, the way the T140 head steady works it’s more likely to ‘load’ the inlet rocker box, the part of the head steady that extends forwards to the ex rocker box is little more than a ‘tuning fork‘ IMHO.

What the stock head steady might be more guilty of IMHO, is loading the rocker box gaskets due to thermal expansion, as the head heats and cools, the rocker boxes will want to move away from and towards each other. Due to this hypothesis, and because it limited access to tightening the head fasteners, and because I could not see how it added any value, I cut it down during this last top end rebuild, so mine only fastens to the inlet box now.

But regarding the road loads, I knew a guy who raced a 750 Nourish T140, he struggled with inner gearbox covers leaking. Removing the head steady cured it, so it can be strange how those road loads manifest themselves sometimes. He left the head steady off, with no ill effect. I’m not brave enough to do that.
 
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When I acquired my "restored" T140, it came with a powder coated frame and stainless bolts/hardware. On my first real ride, the powder coat crushed almost everywhere and multiple stainless nut/bolt connections, being coarse threaded, went loose and fell apart.
Among them, the head steady bolt/bushing went loose, and the bushing/bolt were lost to the road. After I replaced it all, it didn't take long for the rocker box to start leaking. I wondered about it and asked an old hand, a well known tuner, who said "Oh, we always threw those things away, yeah, they got in the way and I think they cause oil leaks."
 
Well, if Sod’s Law don’t get yer, the Law of Unintended Consequences prolly will...

The ’ole T140 is running sweet since the top end job. Musta done sumthin‘ right with the squish etc giving it a bit more oomph, cos the clutch is slipping now at around 6,000rpm. And it wasn’t before.

Its a 7 plate job from LP Williams too, guess Phil was right when he said not to use synthetic oil after all !
 

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