connecting rod clearance

robs ss said:

Arcadians said - "I too have a set of H Beams ready to be installed once the crank is back from balancing"

Arcadian - the penny just dropped with me (slow, I know)
How are you getting your crank balanced (static or dynamic) without the balancer having your rods?
Would seem essential for him to have them.
Rob

Click to expand...

My statement wasn't clear, the crank will be sent out for dynamic balancing (with the rods)... I'm just waiting on my pistons to arrive before sending them off

John B in Bama said:

Acadian,
Curious where you got your steel rods. They definitely are different from the MAP ones with a less intrusive big end cap. I'd be surprised if you had any clearance problems.
And now, once again, I ponder the wisdom of reassembly with original rods. What are the chances of a broken rod with normal use.... Obviously minimal but still the nagging worry and "what if" intrudes. And if you're trying to build with an eye on dependability, the value of the steel rods cannot be denied.
Thanks again for all the ideas and comments.

John B. in Bama

Click to expand...

Don, AKA "madass" on this forum

John B in Bama said:

Acadian,
Curious where you got your steel rods. They definitely are different from the MAP ones with a less intrusive big end cap. I'd be surprised if you had any clearance problems.
And now, once again, I ponder the wisdom of reassembly with original rods. What are the chances of a broken rod with normal use.... Obviously minimal but still the nagging worry and "what if" intrudes. And if you're trying to build with an eye on dependability, the value of the steel rods cannot be denied.
Thanks again for all the ideas and comments.

John B. in Bama

Click to expand...

Dances with Shrapnel said:

To the OP post - steel rods are overkill unless you are building and planning to do something extraordinary with the engine. The factory rods with steel caps are well designed and extremely durable for most Norton big twin applications.

Click to expand...

There are plenty of vintage racers who went decades without even changing the stock aluminum rods. I have raced with these folks and not a hint of trouble. Steve Maney apparently witnessed problems with the factory rods splitting on the small end but only with the 1,007cc race engine(s) and only with these 1,007cc motors pushing in excess of 80 RWHP.

Another downside to steel rods is the increased reciprocating weight, so from a "science" standpoint, you are trading one thing for another. If you really want steel rods, there are lightweight piston & rods which offer reciprocating mass even lower than stock......and there's no fiddling around with grinding bolts or skimming crankcase innards. That's the "engineering" of it. Again, I would not mess with steel rods if you have a good set of factory rods. I mean what's next?...steel crankcases?

acadian said:

Don, AKA "madass" on this forum

Click to expand...

That might be why you have interference issues. Don's rods (which I use and like) come with the 3/8" cap screws, which are larger than the 5/16" ones on Carrillo rods. The rods in the pictures I posted earlier in this thread, with the heads ground for clearance, are Don's. Keep in mind that this is a 93 mm stroker crank, so I probably would have had clearance issues with whatever rods I chose to use.

Ken

Hi Ken , is it possible to find out some cap screws with the 5/16 head ? I had bought a pair of Don's steel rods , and though they are not yet fitted and that my Nourrish crank is not ready (want to fit an alternator end on it ....must find a suitable lathe !), that could be one simple fix , but you had surely think about it before me !!!!

Here it is. The old sits on top of the MAP rod showing the difference in length at the crucial spot. Ken. You've got big ones if you're bold enough to grind off that much bolt head and then race the thing. More power to you;-)

Acadian,
Where did you get your rods?

Thanks again.

Can anyone give contact info. for Don "Madass?"

marinatlas said:

Hi Ken , is it possible to find out some cap screws with the 5/16 head ? I had bought a pair of Don's steel rods , and though they are not yet fitted and that my Nourrish crank is not ready (want to fit an alternator end on it ....must find a suitable lathe !), that could be one simple fix , but you had surely think about it before me !!!!

Click to expand...

I don't know if anyone makes 3/8" diameter connecting rod cap screws with reduced head size, but that would certainly help. You might still be OK with Don's rods and the standard 89 mm stroke. I haven't tried that combination yet, and I have to believe that Don checked for clearance in stock cases before selling his rods.

Ken

Addendum. I fitted "H" beam steel rods from Madass. They weigh just about same as the stock rods and do not project as far as the MAP rods at the cap ends. Still, I had to cut off a shoulder on the big end cap bolts to get clearance. This was for an 850 and I understand crankcase thickness may vary. (The MAP rods were slightly lighter than stock.) Don's were like Acadian's as pictured above. Acadian. Did you have clearance or did you have to modify the bolts? Thanks Ken and all for the ideas and comments.

acadian said:

I too have a set of H Beams ready to be installed once the crank is back from balancing, I'm very interested to hear how this pans out and will be checking the clearance myself as soon as the parts are back in my hands

Edit:

Just went out back and compared my H beam against a stock rod:

Length: stock = 7.875, H beam = 7.625
Width at big end: stock = 2.975, H beam = 2.938

So, it looks like I'm in the clear

Click to expand...

,


Good Morning Together,
First, one question about your conrods: How do you want to make up the difference in the conrod length? Afterall we are talking about 0,25" (6,35mm). Would you add this difference to the compression height of a (custom made) piston, or do you want to mill down the 0,25" from the cylinder barrel of you engine with all the problems which might occur in this case?

Somthing else that very often gets into my mind:
As standard the conrod bolts are inserted into the conrods from below. This necessitates the parting of the crank case in case of retightening the bolts, renewal of the bearing shells or just the inspection of the big end journals. As well as that, it also is the reason why some of the aftermarket conrods don't run free in the crank case. Also if you lengthen your stroke the bolts will very often also touch the walls of the crank case.

Has somebody ever thought about inserting the bolts from above, using a thread (and no nuts) in the conrod cap? I mean from the cylinder base flange? All the boxer- engines (at least BMW, Porsche or VW- Boxer- engines) insert their bolts from the cylinder base flange. So why don't we do the same thing?

Think about it, I'd like to hear your comments. Have a nice sunday.

Best Regards
Klaus Monning

lcrken said:

That might be why you have interference issues. Don's rods (which I use and like) come with the 3/8" cap screws, which are larger than the 5/16" ones on Carrillo rods. The rods in the pictures I posted earlier in this thread, with the heads ground for clearance, are Don's. Keep in mind that this is a 93 mm stroker crank, so I probably would have had clearance issues with whatever rods I chose to use.

Ken

Click to expand...

I don't think I will have clearance issues, Don's rods (the one's I have anyway), seem to provide more clearance than the stock rods:

Length: stock = 7.875, don's H beam = 7.625
Width at big end: stock = 2.975, don's H beam = 2.938

I rebuilt my MKIII engine about a year ago. I pondered for awhile if I wanted to spend $500 for Carrello rods. My rods had 50'000 miles on em and looked perfect. I've seen broken aluminum rods in Triumph, BSA and Norton engines. New crankcases don't fall of the Norton supply truck any more so I sprung for the Carrello rods for peace of mind. The crank had to be rebalanced but I would have done that anyway.