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#844145 03/26/21 1:27 pm
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Man, I hope to not have to bug you all every step of the way of this motor build...
So a65 crank ground to .010 under. New map rods with .010 under (over?) Bearings to match crank.
Dry assembly using plastigage on cap side and I'm getting .003 from it.
Now the plastigage was old, cold and kinda crumbly. That being said I warmed it a little over my space heater so it wouldn't disintegrate when I cut a piece long enough to use for measuring.
I believe tolerance is .0015..
Soooo....
Confused about what I should do at this point. Get new .020 bearings and have crank reground..? That sounds like, well, a pain in the ass and excessive.
Say sod it and clamp em together and run it. mind you I'm hoping to build this to be a NICE motor with all the performance upgrades available within my tax bracket.
I don't plan on racing it but I don't want to think twice about pinning the throttle for a minute or two.
Input is, again, greatly appreciated.
Thanks guys

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Get some new plastigage and check again, also with a good micrometer check the journal diameter is actually 10 thou under std and not 11.5 thou under. If you do have 3 thou of clearance then one of these is wrong or a combination, rod big end eye internal diameter, thickness of shell bearing, crank journals.

PS its 10 thou under as you take metal off the crank journal so its diameter decreases.

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When you checked, was each rod bolt torqued to spec?

Sounds silly, but you would be surprised what the proper torque can do in terms of the proper clearance

You can also use a bore gauge to measure clearance


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i had the same problem ,it was the asian hepolite shells


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Originally Posted by wak
i had the same problem ,it was the asian hepolite shells

Kinda makes me glad I held out for the nos glacier shells I got for mine.


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68’ A65 Lightning “clubman”
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Rechecked with new plastigage. Plastigage on rod side, not cap side. Bolts torqued to spec. Still coming out at .003". map cycle rods and supplies bearings. They are quality.
I'm about to throw the crank through the machine shops window...

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Don't blame it on the crank just yet.

It's a really good idea to install the inserts in the rods, torque them to spec and send them along with the crank. That way the machinist can measure them himself and cross check the published spec with the actual size of the fitted bearings. It saves a lot of grief.

Wak's comment about different shells giving different clearances is a good one. If you were to measure the thickness of a whole set of inserts for a V8, you might find a variation of 4 or 5 tenths between the thickest ones and the thinnest ones. And this is all from the same manufacturer! But this is not all bad because these variations can also be used to selectively fit your bearings to journals that might be a little bigger or smaller.

All that to say, it's a good idea to get another set of bearings from a different manufacturer and try them before grinding your crank again. NOS Vandervells would be really nice but hard to find.

One final thought. If you have the MAP steel rods, the bolts should be tensioned using a stretch gauge. The actual torque often ends up to be more than the foot pound spec to reach the recommended stretch value. This will effect clearance as CBS has mentioned.

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You state the crank is -.010 under

What do the journals actually measure after grinding?

Perhaps we should start there and move forward before ruling anything else out?

Not uncommon for a crank grinder to make a mistake, it's not right, but we are human and things like that do happen...


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Originally Posted by Stuart Kirk
Don't blame it on the crank just yet.

It's a really good idea to install the inserts in the rods, torque them to spec and send them along with the crank. That way the machinist can measure them himself and cross check the published spec with the actual size of the fitted bearings. It saves a lot of grief.

Wak's comment about different shells giving different clearances is a good one. If you were to measure the thickness of a whole set of inserts for a V8, you might find a variation of 4 or 5 tenths between the thickest ones and the thinnest ones. And this is all from the same manufacturer! But this is not all bad because these variations can also be used to selectively fit your bearings to journals that might be a little bigger or smaller.

All that to say, it's a good idea to get another set of bearings from a different manufacturer and try them before grinding your crank again. NOS Vandervells would be really nice but hard to find.

One final thought. If you have the MAP steel rods, the bolts should be tensioned using a stretch gauge. The actual torque often ends up to be more than the foot pound spec to reach the recommended stretch value. This will effect clearance as CBS has mentioned.

I had a set of MAP rods that I tried to stretch the bolts to required length. One of the bolts showed no stretch at 40 ft lbs torque. This concerned me and I called ARP for advice. I was told to just use the torque figure in the instructions and not worry about it. I did and that motor went 2 seasons of racing without issue.
I could not agree more with those that recommend measuring everything. Until you measure, you do not know.

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What Mike says...^^^^^^^. Marino told me using a torque wrench is just fine..
I told a story recently of the main bearing bush clearance on my A10...Shop said they machined the crank to .0015 on both the main and rods...At home assembling the engine The Kibblewhite main bush was too thick ,no side clearance and jamming the crank.Took it to a more local shop to have it milled...Asked shop to measure the crank and bush clearance, they said it was nearly .003...hmmm...So I spend money on reasonable quality 2 inch mike and bore gauges... My measured clearance is .0015 to .0017....
You never know.......


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“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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I retold this the other day but here it is again.

I did a rebuild on a motor for a friend a few years ago. Everything about the engine was unknown so I went though it all piece by piece. I measured the crank and it was about 0.003” under standard, not a mark on the journal and it was perfectly round. Same for the TS journal. So I took the crank and the micrometer into the house and left it over night in the warmth. Took my measurements again the next day and everything was spot on.

That was 6 years ago and the bike is still running well now. I’m not sure what the temperature is like up in Oregon. But I’m guessing it’s still fairly cool in the garage? Leave it in the warmth of the house over night and measure it again. Bring your rods and your shells in too.


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Originally Posted by Mike Baker
I had a set of MAP rods ......... One of the bolts showed no stretch at 40 ft lbs torque. This concerned me and I called ARP for advice. I was told to just use the torque figure in the instructions and not worry about it.
ARP does give very specific torqueing recommendations, use their special lube, burnish the threads and thrust faces by torqueing several times before a final tensioning, use a stretch gauge, but also defers to the rod manufacturer for specific values. Would probably be better to contact MAP for their rod bolt tensioning specs.

Sometimes the published torque spec will be exceeded to get to recommended bolt stretch. I have seen that many times. Going by a stretch value avoids variations in friction that can greatly influence proper installation.

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There’s absolutely no way in which increasing torque = stress on a bolt doesn’t increase its length.

So for Mike to say 40 ftlbs didn’t produce any extension at all doesn’t make sense.
I can only imagine that the ends of his micrometer weren’t in the right places, also hard to believe.

40lbft would seriously compromise most rod bolts, taking them beyond their elastic limit.

So how would ARP understand this I wonder? Does 1 bolt in 4 disobey the laws of physics?

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Ok, here's more info. I have my basket case '59 BSA A10 engine apart.

The crank is freshly reground with those Hepolite inserts in MAP rods.

The inserts were installed in the rods and the bolts tensioned to MAP's stretch specs before going off to the machine shop.

The machinist was instructed to measure out the rods and go by that dimension when grinding.
[Linked Image from i.postimg.cc]
So I went and measured the rod journals...

BSA's first regrind calls for 1.677" to 1.6765". These journals measure out at 1.678".

That is a thou to a thou and a half larger than recommended. This would make up for the Hepolite shells being thinner than they should be.
[Linked Image from i.postimg.cc]
This tells me that those Hepolite inserts are indeed sized incorrectly for a crank that is reground to BSA specs.

So Drunkenmonkz, Don't toss that crank anywhere, get yourself another set of inserts from someone besides Hepolite and try them.

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Originally Posted by koan58
There’s absolutely no way in which increasing torque = stress on a bolt doesn’t increase its length.

So for Mike to say 40 ftlbs didn’t produce any extension at all doesn’t make sense.
I can only imagine that the ends of his micrometer weren’t in the right places, also hard to believe.

40lbft would seriously compromise most rod bolts, taking them beyond their elastic limit.

So how would ARP understand this I wonder? Does 1 bolt in 4 disobey the laws of physics?

To be clear, all bolts were lubed and burnished as per the instructions. None of the 4 bolts showed the same stretch for a given torque figure, however, 3 of them were close enough for comfort. The 4th acted completely different. It didn't make sense to me either.
I suppose I'm a bit like Tony. Maybe what we do doesn't fit into a perfectly made box but it works, to the chagrin of the experts. We're not afraid to try things. When the choice is between racing and mental masturbation, I'll choose racing.

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I believe as a hobbyist mechanic I 'm far more likely to make a mistake fussing around with bolt stretch and micrometers than a simple tool like a torque wrench...And yes, torque wrench can be used incorrectly..


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Mike Baker
Originally Posted by koan58
So how would ARP understand this I wonder? Does 1 bolt in 4 disobey the laws of physics?
None of the 4 bolts showed the same stretch for a given torque figure.......The 4th acted completely different. It didn't make sense to me either.
ARP would probably say there is a problem with the lube or the threads. Either one could cause extra friction resulting in less stretch for a given torque setting..

What you could do is to remove the problem bolt, clean all that black sticky lube off of it and inspect it with a 10 power magnifying glass looking for defects in the thread. If the thread peaks are a bit rounded and shiny near the end of the bolt, that could be an incompletely tapped hole in the rod binding the thread. Thoroughly clean out the bolt hole in the rod and make sure those threads look ok. If there's no defects, lube the heck out of the bolt and hole and try it again.

If there's still a problem, try switching the bolts to a different hole.

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That is a very plausible explanation.
If it is the case, that bolt won't be remotely stretched correctly and will be prone to fatigue failure.

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Originally Posted by Hillbilly bike
I believe as a hobbyist mechanic I 'm far more likely to make a mistake fussing around with bolt stretch and micrometers than a simple tool like a torque wrench...And yes, torque wrench can be used incorrectly..
Hi HB,
Those stretch gauges are fussy to use and expensive too. I personally like to use a dog bone type adapter for the torque wrench. This allows the stretch gauge to be on the bolt while torqueing. That way I can watch the bolt stretch in real time rather than do a torque and then check stretch after the deed is done.

But having said all that, modern ARP stuff is so much better than OEM from the 60's or 70's that torqueing alone probably is safe enough for most use.....

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Originally Posted by Stuart Kirk
Ok, here's more info. I have my basket case '59 BSA A10 engine apart.

The crank is freshly reground with those Hepolite inserts in MAP rods.

The inserts were installed in the rods and the bolts tensioned to MAP's stretch specs before going off to the machine shop.

The machinist was instructed to measure out the rods and go by that dimension when grinding.
[Linked Image from i.postimg.cc]
So I went and measured the rod journals...

BSA's first regrind calls for 1.677" to 1.6765". These journals measure out at 1.678".

That is a thou to a thou and a half larger than recommended. This would make up for the Hepolite shells being thinner than they should be.
[Linked Image from i.postimg.cc]
This tells me that those Hepolite inserts are indeed sized incorrectly for a crank that is reground to BSA specs.

So Drunkenmonkz, Don't toss that crank anywhere, get yourself another set of inserts from someone besides Hepolite and try them.


The rod shells are made by Glacier/Vandervell in the uk and what come with the map cycles rods. Pretty good quality.
I micrometered everything and did the math and came up with an acceptable tolerance. Then I threw the plastigage away...

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Definitely was cold when I started piecing it together. It's warming up now. Thankfully! I micrometered everything, did the math and came up with an acceptable tolerance that I'm going with. I promptly threw the plastigage in the garbage bin.
Thanks!

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Originally Posted by Stuart Kirk
Originally Posted by Hillbilly bike
I believe as a hobbyist mechanic I 'm far more likely to make a mistake fussing around with bolt stretch and micrometers than a simple tool like a torque wrench...And yes, torque wrench can be used incorrectly..
Hi HB,
Those stretch gauges are fussy to use and expensive too. I personally like to use a dog bone type adapter for the torque wrench. This allows the stretch gauge to be on the bolt while torqueing. That way I can watch the bolt stretch in real time rather than do a torque and then check stretch after the deed is done.

But having said all that, modern ARP stuff is so much better than OEM from the 60's or 70's that torqueing alone probably is safe enough for most use.....
Originally Posted by Stuart Kirk
Originally Posted by Hillbilly bike
I believe as a hobbyist mechanic I 'm far more likely to make a mistake fussing around with bolt stretch and micrometers than a simple tool like a torque wrench...And yes, torque wrench can be used incorrectly..
Hi HB,
Those stretch gauges are fussy to use and expensive too. I personally like to use a dog bone type adapter for the torque wrench. This allows the stretch gauge to be on the bolt while torqueing. That way I can watch the bolt stretch in real time rather than do a torque and then check stretch after the deed is done.

But having said all that, modern ARP stuff is so much better than OEM from the 60's or 70's that torqueing alone probably is safe enough for most use.....
How many BSA and Triumph engines with properly torqued stock rod bolts have had a bolt failure even when racing?


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Originally Posted by Hillbilly bike
How many BSA and Triumph engines with properly torqued stock rod bolts have had a bolt failure even when racing?
Yeah. More likely lubrication or piston problems.

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Originally Posted by drunkenmonkz
Definitely was cold when I started piecing it together. It's warming up now. Thankfully! I micrometered everything, did the math and came up with an acceptable tolerance that I'm going with. I promptly threw the plastigage in the garbage bin.
Thanks!
I'm glad it all worked out. You probably got way more help than you expected.

And yes, plastigage isn't always accurate.

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Originally Posted by Stuart Kirk
But having said all that, modern ARP stuff is so much better than OEM from the 60's or 70's that torqueing alone probably is safe enough for most use.....
I assembled mine using ARP bolts and stock rods and caps. I used bolt stretch when I tightened and checked the torque. It was right at the specified torque value, so I guess you are correct.
I suppose I could (should) have used Plastigage to check clearances, but I don't really like the idea of torquing these nuts, removing them to check, then reusing the same bolts and nuts.


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