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Discussion Starter · #1 ·
68,750 longrod To start with I fucked up running my engine in the first time, blew a base gasket fangin around too hard doin the ton etc, on inspection of pistons found detonation mark on crowns.Tidied them up with new rings and rehoned the bores myself using one of those 3 pronged/sprung, use the drill method, I think I used kero then washed w/soapy water and wipe thoroughly w/ paper wipes.
The score marks looked the same as a prof. done job on norton barrels I have in wait.
I dont run a speedo so I'm guessing it should be near run in, 4 short rides ago I changed oil from Lucas 30 run in oil to Penrite 20/50 bike oil.
Comp is. Cold test: 125/150. Wet 150/150. Hot test: 115/125. No wet hot test.
The bike runs crisp and hard when I give it a bit, not owning a comp tester before I can just FEEL when it's run in, now I have questions:
Is it normal sometimes for one to lag behind the other?
Obviously I'll just keep checking as time passes and as the rings bed in better I'll FEEL that too, or may it never bed properly, I know they do this from pussyfooting around at low revs but I haven'y been doing that, even riding along the freeway I slow down and squirt it to make 'em bite.
Probably spoken a lot before but a proper run in makes the motor, interested in what you guys have noticed.
Shouldn't have bought that bloody tester, it's got me thinkin' too much!
 

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I think he is wondering if it is normal For his cylinders to be so far apart in psi wet cold and hot. He was used to doing it by feel before, but now has a new tool that has him second guessing his old way of doing things.

The lower sided cylinder may have some tired valve parts or guides or even something else affecting pressures. As for the numbers themselves, honestly I have no clue what normal is for a 68 stroked trump, but a ton of guys here will know.

The comp tester is good, you just have to get used to putting that new information in line with what you know.
 

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Strange that the hot test is about 20 psi lower than the cold compression test.It should be more on a hot engine.What cams and valve clearances are you using?

I've seen 170 psi on a 9:1 engine 5 minutes after start-up after a rebore.I would suspect the compression gauge.

Detonation is usually caused by too much timing advance or too high compression ratio.Not enough revs can do it too,if the timing is fully advanced below about 3500 rpm.
 

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/\ /\ dem's screwy or at least a*se about face clearances , no?

yep, compression gauge gives you something else to think about. My understanding is 80 = sh*gged , my '72 650 reads 112 - 115 cold and it pulls plenty hard.

But then again as they say, ' if some is good, more is better and too much should just be about right'.
 

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No;they're correct clearances.Valve clearance must suit the cam profile.T140 intake cam has a quietening ramp,and needs 0.008" valve clearance.3134 exhaust cam does not have that quietening ramp.
 

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Discussion Starter · #10 ·
Breathing through 3/8" holes drilled into and out of front cavity which is filled with a ss scour pad. a few inches above the exit is a housed BMW reed valve, 3/8" hose goes into the front downtube, up past lower stem bearing all the way down to bottom of rear down tube.

Pete, I have been doin .04" IN - .06" EX
 
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