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Sorted! How tight should a big end be? #300774
02/28/10 8:23 pm
02/28/10 8:23 pm
Joined: Aug 2001
Posts: 918
hampshire, england
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t120mike Offline OP
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hampshire, england
OK so I am doing the first "wet" assembly of my project and I am a bit nervy about it! I have got a new Nourish crank and new (NB)steel rods where both the crankpins and big ends are to the Triumph 650 spec using stock big end shells. The big ends are assembled with clean engine oil and torqued up. They rotate fine but are not quite as loose as I expected. They seem just a tad tighter than when I "dry" assembled them (but then I only nipped up the nuts to close the cap on). Before I close the cases, can anyone who does dozens of these things please tell me how sloppy or tight these things should feel when brand spanking new?
Grateful!

Last edited by t120mike; 03/01/10 7:15 pm.

mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
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Re: How tight should a big end be? [Re: t120mike] #300781
02/28/10 9:40 pm
02/28/10 9:40 pm
Joined: Oct 2007
Posts: 727
bromley uk
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norton bob Offline
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bromley uk
Im not an engine specialist but for sure they should fall under thier own weight,I would take the rods off, torque up and check the bore size and the crank, also look for ovality and do a plastigauge check.Also check side clearance.

Last edited by norton bob; 02/28/10 9:41 pm.
Re: How tight should a big end be? [Re: norton bob] #300800
02/28/10 10:52 pm
02/28/10 10:52 pm
Joined: Aug 2001
Posts: 918
hampshire, england
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t120mike Offline OP
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Tks Bob.

They fall easily under their own weight, alright, and the dimensions of crank pin and big end bore are not in question.

To illustrate: The engine is on its side and I can push the little ends around with the tip of a 15 thou feeler guage (3.5" long) but not with a 10 thou (it bends and goes past). Now the oil may be cold and the rod is hanging sideways which might add a little to the friction.

Does that illustration give a better "feel" for the issue?


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
Re: How tight should a big end be? [Re: t120mike] #300850
03/01/10 5:19 am
03/01/10 5:19 am
Joined: Jan 2009
Posts: 872
QLD, Australia
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RetroRod Offline
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QLD, Australia
Originally Posted By: t120mike
OK so I am doing the first "wet" assembly of my project and I am a bit nervy about it! I have got a new Nourish crank and new (NB)steel rods where both the crankpins and big ends are to the Triumph 650 spec using stock big end shells. The big ends are assembled with clean engine oil and torqued up. They rotate fine but are not quite as loose as I expected. They seem just a tad tighter than when I "dry" assembled them (but then I only nipped up the nuts to close the cap on). Before I close the cases, can anyone who does dozens of these things please tell me how sloppy or tight these things should feel when brand spanking new?
Grateful!


The workshop manual refers to diametral clearance of the big end to be between .005" to .020". I presume this to be the overall amount of free space between the crank and the bearing surface (best to worst).

I'd use plastigauge to actually measure what clearance you have with the caps torqued. I've seen many refer to the "fall under their own weight" test, which may well be reliable, but measuring is the only objective means of knowing for sure. A fly fart too tight you're in trouble. RR

Last edited by RetroRod; 03/01/10 5:21 am.

'72 Bonneville
"He who praises you for what you lack wishes to take from you what you have." - Don Juan Manuel
Re: How tight should a big end be? [Re: RetroRod] #300863
03/01/10 9:44 am
03/01/10 9:44 am
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Posts: 727
bromley uk
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norton bob Offline
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As the rods and crank come from different sources i would wonder if theres suff side clearance.I very much identify with fly fart terminology,but how do i measure that!!.Loose has to be better than tight,the orriginal worn (ridged!)50 year old crank in my norton was polished smooth with emery tape and refitted 15 years ago,most likely well outside max clearance,still runs fine with easy classic use.

Last edited by norton bob; 03/01/10 9:53 am.
Re: How tight should a big end be? [Re: norton bob] #300865
03/01/10 10:02 am
03/01/10 10:02 am
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QLD, Australia
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RetroRod Offline
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Hey Bob,

Good to hear from you. Like you, I claim no great knowledge on this topic and probably should have kept out of it. I do hope that Mike gets some experienced ones here to assist.

Journal side clearance is recommended at.012"-.016" and this is not going to hard to determine, surely?

I was thinking more of the diametral clearance, and from a common sense point of view I guess, what I wanted to convey to Mike was that if the minimum diametral clearance is .005" and his measuring revealed a .004" clearance, then this, IMHO, is a fly fart too tight. Better a fly fart more clearance then a fly fart less I would think

Naturally I am quick to bow to weightier opinions, and learn something along the way. RR

Last edited by RetroRod; 03/01/10 10:08 am.

'72 Bonneville
"He who praises you for what you lack wishes to take from you what you have." - Don Juan Manuel
Re: How tight should a big end be? [Re: RetroRod] #300878
03/01/10 2:08 pm
03/01/10 2:08 pm
Joined: Aug 2001
Posts: 7,602
scotland
triton thrasher Offline
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scotland
Originally Posted By: RetroRod
The workshop manual refers to diametral clearance of the big end to be between .005" to .020".



20 thou? That sounds a bit big for a big end clearance.


Amateur Loctite enthusiast.
Sorted! How tight should a big end be? [Re: triton thrasher] #300919
03/01/10 7:25 pm
03/01/10 7:25 pm
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Posts: 918
hampshire, england
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t120mike Offline OP
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Sorted!

Thanks all for all the sage advice. I also took advice from some professionals. Both were reassuring BUT Hughie Hancox (thanks Hughie) advocated seating the bearing shells by taking a soft drift to the big-end bolt heads and giving them each a smart tap. As I haven't got bolts but studs, I decided to give the (steel) end-caps a twack with a copper mallet as well as another thwack to the small end (steel rods!!!). Worked a treat and the rods turn really free without being sloppy.

I'm going with that! Closing the cases tonight

Thanks for all your comments, guys


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
Re: How tight should a big end be? [Re: triton thrasher] #300934
03/01/10 9:38 pm
03/01/10 9:38 pm
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QLD, Australia
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RetroRod Offline
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I'm losing it thrasher. Funny you raise this as this was my own immediate feeling. The reality is .0005"-.002". Don't listen to me!

I knew I should have kept out of this. But I won't forget this clearance!! RR


'72 Bonneville
"He who praises you for what you lack wishes to take from you what you have." - Don Juan Manuel
Re: How tight should a big end be? [Re: RetroRod] #301056
03/03/10 1:39 am
03/03/10 1:39 am
Joined: Mar 2005
Posts: 10,221
Boston, Massachusetts
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John Healy Offline
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Boston, Massachusetts
The correct clearance for the Triumph rod bearings is 0.0005" to 0.002."

1. Because these rods have never been on this crank before I would "prove" everything before assembly!
a. Before placing the shells into the rods measure the bore diameter of the rod. It should be 1.770".
b. Before placing the rods onto the crankshaft, install the rod bearing shells into the rods and bring the bolts to full torque. Measure the shell diameter top to bottom (not side to side as the shells are not round).
c. Compare the dimension with the crankshaft journal. Clearance should be within tolerance above - 0.0005" to 0.002".

2. Be sure the rod is cut deep enough to accept the bearing shell anti-rotation tang. If it isn't the clearance will tighten up as the bolts are tightened. Be sure that the shell only sticks up above the rod split a couple of thousandths (approx. 0.002" to 0.004"). If it is too much it will distort the shell when rod bolts are tightened. If it isn't the shell will not be clamped properly into the rod.

3. Generally speaking the rod should not be turned before the the rod nuts are taken to full torque. Rods should never be turned with out being lubricated first.

4. Pre-lube the shells with engine oil, or assembly oil (assembly lube will not let the rod fall as freely as engine oil, but the rod still still fall of its own weight).

5. As mentioned above the side play is 0.0012 to 0.0016". A couple of thousandths more will not hurt anything, but not less than 0.012".

6. If required (example using ARP rod bolts) be sure to follow their tightening sequence - tighten to full torque 5 to 6 times before taking final rod bolt measurement. Be use to use their bolt thread lubricant!

7. If there is any binding as you rotate the rod it must be corrected before the engine is used. At 0.002" rod bearing clearance you should not be able to detect ANY movement as you pull and push the rod!

You totally lost me when the hammer came out! If I calculate this right, you have just under 1500 pounds Sterling into the rods and crankshaft. I think its time to break out the micrometer and dial gauges, not the hammer, brass or not.


Re: How tight should a big end be? [Re: John Healy] #306253
04/03/10 2:53 am
04/03/10 2:53 am
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Posts: 728
angeles city, rp
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jaycee Offline
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roger that!


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