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I used to have a 70 T100 twin. I saw a picture of the rocker box on a 73 500 twin and it had a hex head plug near each of the rocker arm ends that my 70 did not have. What are these for? Better access during valve adjustments?

[Linked Image from i.imgur.com]

Last edited by nat_mann; 04/20/22 10:03 pm.
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For feeler gauge access, yes.

I think I heard those plugs are inclined to leak oil.


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[Linked Image from i.postimg.cc]

Last edited by L.A.B.; 04/20/22 11:08 pm.
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Introduced in 1971/2 but not kept on the 650/ 750s after that. Just seal them up, they are useless anyway!


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Originally Posted by triton thrasher
For feeler gauge access, yes.

I think I heard those plugs are inclined to leak oil.
True but use O-rings and they stay oil tight and stay put.
Originally Posted by tiger_cub
Introduced in 1971/2 but not kept on the 650/ 750s after that. Just seal them up, they are useless anyway!
I don't think they're useless but I still don't use them as I don't use feeler gauges at all on the 2 thou/4 thou sports cams.

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I never used 'em on my '72 500.

Easier to go in from the top with a bend feeler gauge....the "traditional way."

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Or use the method where you calculate the turn of the tappet screw. That more takes into account the possibility of a small wear & tear dip in the top of the valve.

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Hi Nat, Yes they are for feeler gauge access. I personally like them & used them on the later 650s. A small smear of Hylomar & new copper seals every time prevents leaks/seeps.

I would wager most owners got a closer adjustment even if the tip of valve was worn. I've seen many owners adjust the intakes too tight by the turn method. Soon valves were being held open cold. The exhausts were more forgiving due to you turned them twice as much. Obviously skilled owners adjust with turn method no problem. Most owners now are skilled & experienced. Back in the early 70s that was often not the case.
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Originally Posted by TR7RVMan
I would wager most owners got a closer adjustment even if the tip of valve was worn. I've seen many owners adjust the intakes too tight by the turn method. Soon valves were being held open cold. The exhausts were more forgiving due to you turned them twice as much. Obviously skilled owners adjust with turn method no problem.

The 0.002” inlet clearance in the 650 and 500 manuals is a bit small for safety.

I expect we’ve all seen the American 650 service note that recommends 0.004” inlet and 0.006” exhaust.


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...iron heads have almost nil clearances.

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Originally Posted by reverb
...iron heads have almost nil clearances.

Generally, iron head models get the same clearances as alloy head, if the same cams are used.

Before they introduced the E3275 ramp cams, the recommended clearance was 0.001”.


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Originally Posted by triton thrasher
Originally Posted by TR7RVMan
I would wager most owners got a closer adjustment even if the tip of valve was worn. I've seen many owners adjust the intakes too tight by the turn method. Soon valves were being held open cold. The exhausts were more forgiving due to you turned them twice as much. Obviously skilled owners adjust with turn method no problem.

The 0.002” inlet clearance in the 650 and 500 manuals is a bit small for safety.

I expect we’ve all seen the American 650 service note that recommends 0.004” inlet and 0.006” exhaust.
It's what I use. Gives one some more time before the gap inevitably closes up, especially before the engine has settled in properly.

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Hi , When I was at Harley dealer, iron head Sportster clearance cold was just free! Aluminum push rods. I guess the iron was so hot it expanded more than push rod. You had to stay on top of adjustment. Fist sign of clearance problem was hard starting. Next was burnt valves. However they proved durable & the system worked good.
Big motors had hydraulic lifters. That made life simple!

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Originally Posted by TR7RVMan
Hi , When I was at Harley dealer, iron head Sportster clearance cold was just free! Aluminum push rods. I guess the iron was so hot it expanded more than push rod. You had to stay on top of adjustment. Fist sign of clearance problem was hard starting. Next was burnt valves…
Don

Zero cold clearance was common on old Brit singles, AJS/Matchless and Enfield for example. They had a sort of obsession with mechanical quietness.

For the reasons you state, it really was wiser to give them a couple of thousandths of an inch gap.


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.002" is in effect "just free". I too prefer a bit more. A Triumph engine is so noisy anyway, I can't hear any difference.

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A loose tappet is a happy tappet!


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If it wasn't tapping, it wouldn't be a tappet, would it?

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Within reason, how critical is it anyway? On his car, if my dad could spin the pushrods, the job was done.

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Originally Posted by DUHC
Within reason, how critical is it anyway? On his car, if my dad could spin the pushrods, the job was done.

Too small a gap can be critical.


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Agreed, I get that, but I was thinking, and should have been clearer, on erring on the side of a bigger gap, when talking of advised 2 or 4 thou cold gaps. As Stein Roger hints, that 2 thou cold gap may largely disappear when the engine gets hot.

For example, on my all iron Riley engine it advises 3 and 4 thou gaps, but adjusted when hot.

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I have E3134 profile cams in an iron head T110 with oversized valves and I set the gaps to 0.008” all round.


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Used those side access holes for the first time yesterday,
Glad I did as they were little more than finger tight
I like them a lot. Went from 2 and 4 to 4 and 6.
Thanks for the input, gentlemen


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Originally Posted by triton thrasher
A loose tappet is a happy tappet!
Originally Posted by TinkererToo
If it wasn't tapping, it wouldn't be a tappet, would it?
You guys! laughing


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