29-04-2021, 11:01 AM
(This post was last modified: 29-04-2021, 11:03 AM by Hedd_Jones.)
Steve
Sounds like a proper bit of fitting, rather than swapping parts which is the norm nowadays.
With respect to tightness of a big end, and having done a bit of this sort of thing. I was taught that you want the rod to be able to rotate on the crank under its own weight. if it won't its too tight.
How loose it needs to be on the rod is more subjective!. Using something like plasti-gauge here works well in the absence of proper engineering grade measuring tackle.
With respect to the bolt tightness, there will be someone on here will quote some torque or another, and for highly stressed engines I will not disagree with the theory that it is good everything is equal and 'tight'. However when doing this sort of fitting work you will very quickly learn that the tightness of the bearing is often dependent on how tight you do the bolt up. I cant really convey on the computer what I think would be OK, I had my dad double check me when I was learning such dubious skills. Nylock nuts are a godsend in this application. What you need to remember is the bolts are in the general scheme of things pretty small, and a decent spanner puts easily the necessary torque on the fixings.
So how to get your tight big ends to fit. Do you have blue? blue them and see where they touch, scrape the high spots. Slowly slowly. a bit at a time. If you believe they are somewhere near, Timesaver lapping compound is good (so long as you keep it wet), if your bearings are really tight and seem to fit the journal well, you might need to shim the cap out.
I am fully aware that there will be forum readers swearing at the screen of their computers, frothing at the mouth ''you can't do that!'', but I would contend, that, yes, actually you can. People have been doing it for decades. Indeed when our cars were being maintained in the years immediately pre war and later, this would have been commonplace.
Please, if you bought that Speedy Crankcase on e-bay, and plan on 24hours at LeMans - don't do it, but if your building what might be a spare engine for emergency use out of 'sh1t' get stuck right in. If your somewhere in the middle, take a view.
Sounds like a proper bit of fitting, rather than swapping parts which is the norm nowadays.
With respect to tightness of a big end, and having done a bit of this sort of thing. I was taught that you want the rod to be able to rotate on the crank under its own weight. if it won't its too tight.
How loose it needs to be on the rod is more subjective!. Using something like plasti-gauge here works well in the absence of proper engineering grade measuring tackle.
With respect to the bolt tightness, there will be someone on here will quote some torque or another, and for highly stressed engines I will not disagree with the theory that it is good everything is equal and 'tight'. However when doing this sort of fitting work you will very quickly learn that the tightness of the bearing is often dependent on how tight you do the bolt up. I cant really convey on the computer what I think would be OK, I had my dad double check me when I was learning such dubious skills. Nylock nuts are a godsend in this application. What you need to remember is the bolts are in the general scheme of things pretty small, and a decent spanner puts easily the necessary torque on the fixings.
So how to get your tight big ends to fit. Do you have blue? blue them and see where they touch, scrape the high spots. Slowly slowly. a bit at a time. If you believe they are somewhere near, Timesaver lapping compound is good (so long as you keep it wet), if your bearings are really tight and seem to fit the journal well, you might need to shim the cap out.
I am fully aware that there will be forum readers swearing at the screen of their computers, frothing at the mouth ''you can't do that!'', but I would contend, that, yes, actually you can. People have been doing it for decades. Indeed when our cars were being maintained in the years immediately pre war and later, this would have been commonplace.
Please, if you bought that Speedy Crankcase on e-bay, and plan on 24hours at LeMans - don't do it, but if your building what might be a spare engine for emergency use out of 'sh1t' get stuck right in. If your somewhere in the middle, take a view.