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What are the recommended clearances for both intake and exhaust when using bronze valve guides? I have seen comments ranging from 1.5-3 mils for intake and 2.5-3.5 mils for exhaust, which is mostly in the range of the spec in the service manual for iron guides (1-3 for intake, 3-5 for exhaust). This doesn't make much sense to me if you are supposed to allow additional clearance for the bronze guide to expand compared to the iron.
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TR2/3/3A Manganese Bronze Valve Guide Clearance
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TR3driver
Great Pumpkin - R.I.P
Offline
I believe those are oversizes for the guides; total clearance would be that number plus .0005" to .0015" for the stem undersize.
IOW, normally the intake guides would be reamed to 5/16" +/- .0005" but with bronze guides, they should be reamed to 5/16" + .002" +/- .0005" (.314" to .315"). Then the stem should be .310" to .311", so the total is .004" to .005".
IOW, normally the intake guides would be reamed to 5/16" +/- .0005" but with bronze guides, they should be reamed to 5/16" + .002" +/- .0005" (.314" to .315"). Then the stem should be .310" to .311", so the total is .004" to .005".
TR3driver
Great Pumpkin - R.I.P
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Sounds right.
TR3driver
Great Pumpkin - R.I.P
Offline
Right. Unfortunately, I tend to think in inches. Sorry for any confusion.
TR3driver
Great Pumpkin - R.I.P
Offline
It's hard to see, but the part of the valve that goes through the spring retainer is always 5/16". So on the 3/8" valves, you can see a transition in size between the retainer and guide top.
FWIW, I just found some interesting (to me) valve train videos at https://www.engr.colostate.edu/~dga/high_speed_video/#Mechanisms
Got the link from Larry Young's excellent web site on camshaft design and valve dynamics at https://www.tildentechnologies.com/index.html
FWIW, I just found some interesting (to me) valve train videos at https://www.engr.colostate.edu/~dga/high_speed_video/#Mechanisms
Got the link from Larry Young's excellent web site on camshaft design and valve dynamics at https://www.tildentechnologies.com/index.html
groupdeville
Jedi Hopeful
Offline
And carefully measure the bronze guide after they've been inserted and reamed. Despite the clearance specs that you hand over to the machine shop owner, the guy doing the actual work may not know or care not a rat's patootie about bronze, and will ream your guides to the (tighter) cast-iron valve stem clearances.
Then, as your newly assembled TR engine goes on it's first spirited run, the valves will stick open and you'll have to pull the head to correct the incorrect work. Been there, done that - so "trust but verify" should be your motto going forward, even if (as in my case) the shop comes well-recommended.
Then, as your newly assembled TR engine goes on it's first spirited run, the valves will stick open and you'll have to pull the head to correct the incorrect work. Been there, done that - so "trust but verify" should be your motto going forward, even if (as in my case) the shop comes well-recommended.
charleyf
Luke Skywalker
Online
Randall,
I believe I may have an engine that is suffering from improper valve guide reaming and i want to make sure that i fully understand this subject.
I am confused about the additions and totals that are being presented here.
I see that you suggest that the additional reaming for the bronze guides needs to be .002" then the tolerances would be +/- ,0005-.0015". That total would be .0025 to .0035" yet it is stated that the total is 3 to 5 mil for the intake. It looks to me like that should be 2.5 to 3.5 mil. rather than the full 3 to 5. What am I doing wrong here? The same goes for the exhaust guides at 5 to 7 mils.
TR3driver
Great Pumpkin - R.I.P
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Hi Charley,
Sorry for the delay, I just now saw this.
I was using the numbers I got from Ken Gillanders (RIP) many moons ago; which are an extra .002" for intake and .0025" to .003" on exhaust. Not exactly the same numbers the OP mentioned.
Intakes don't get as hot, so they don't need as much clearance, plus excess clearance lets oil get into the cylinders. Exhaust can get quite a bit hotter, doesn't leak as much (no manifold vacuum to pull oil through the guides), and any oil that does get through just burns harmlessly in the exhaust.
Sorry for the delay, I just now saw this.
I was using the numbers I got from Ken Gillanders (RIP) many moons ago; which are an extra .002" for intake and .0025" to .003" on exhaust. Not exactly the same numbers the OP mentioned.
Intakes don't get as hot, so they don't need as much clearance, plus excess clearance lets oil get into the cylinders. Exhaust can get quite a bit hotter, doesn't leak as much (no manifold vacuum to pull oil through the guides), and any oil that does get through just burns harmlessly in the exhaust.
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