Offset wrist pin bushing
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From: Raleigh, NC
Offset wrist pin bushing
Alright so I have aftermarket Crower rods for my motor that use 20mm pins; and I'd like to bush them to 17mm but also move the hole about 1 to 1.2mm up. Question is would the bushing be too thin at the top? Would the bushing rotate after long use? Would it be better to completely remove the old bushing, install a new one and then bore it?
This is for a JDM D15B VTEC with CBR1000RR pistons by the way. I already have the rods and the pistons.
This is for a JDM D15B VTEC with CBR1000RR pistons by the way. I already have the rods and the pistons.
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From: Raleigh, NC
Re: Offset wrist pin bushing
The offset is actually to bring it closer to the head. If it walks any way it'll move farther from the head. Though, since I'm using pretty light pistons I wonder if I can get away with tight clearances(~.025-.027" p-h clearance)
Re: Offset wrist pin bushing
As long as you are aware and are calculating that in then you'll be fine. However, alot of people on here are not knowledgable enough to know figure that out for themselves or that the CR will be effected....sounds like you have it under control though. I would remove the old one and have a new one pressed it....shouldn't have a problem with it moving, especially if you use full float.
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From: Raleigh, NC
Re: Offset wrist pin bushing
Yeah I think I'll just get new pin bushings. I talked with the machine shop that does many race cars and they said they can do it any way I'd like and make it work, but they never done anything like that before and I haven't found anyone using bushings with an offset bore. Just thought I'd ask on here since there's a larger knowledge-base here.
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From: Houston, TX
Re: Offset wrist pin bushing
Where is the piston in relation to the head as is? You're actually wanting to move the piston ~.040" closer?
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From: Raleigh, NC
Re: Offset wrist pin bushing
If I were to bush the rods and retain the center, it'll be about .045" from zero-deck(so figure that plus HG thickness for piston-head clearance). My plan is to get piston as close to deck as possible and use the head gasket to set the clearance. Goal is to reduce the amount of area between piston and head to make the quench pads more effective; literally by using the head gasket to account for rod stretch at higher RPM.
The rod is about as light as LS rods(Crower Maxi-Light, at ~447g with hardware) and the piston is lighter than stock(it's 1mm OS but the design has shorter skirt, smaller diameter pin, and shorter compression height). Safe to assume about .025-.027" rod stretch is safe?
The rod is about as light as LS rods(Crower Maxi-Light, at ~447g with hardware) and the piston is lighter than stock(it's 1mm OS but the design has shorter skirt, smaller diameter pin, and shorter compression height). Safe to assume about .025-.027" rod stretch is safe?
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From: Ben Lomond, Ca, USA
Re: Offset wrist pin bushing
It would be best to calculate the stretch and then provide margin. To do that, you'll need to decide what your rev limiter will be set to, the rod length, the rod beam cross sectional area, the stroke and the weight of the piston, rings, pin and small end of rod. Determine the acceleration through TDC at the rev limit and then the force applied to the beam as a result of the combined weights described previously. Determine the stress by dividing the force by the minimum beam cross section. Determine the strain by dividing the stress by young's modulus for the rod material (steel ~ 30e6 psi). The calculated strain will have units of in/in and so the actual rod stretch will be the strain times the length of the beam if we assume the big end stays nearly round.
You will be amazed at the force exerted on the rod beam. It is proportional to rpm^2 and so over revving is dangerous with tight piston to head clearances.
You will be amazed at the force exerted on the rod beam. It is proportional to rpm^2 and so over revving is dangerous with tight piston to head clearances.
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From: Raleigh, NC
Re: Offset wrist pin bushing
Is there a huge difference between different compositions of steel? Plus, I wouldn't know how to accurately calculate the cross sectional area without fully modeling the rod(which would most likely introduce a lot of areas on my part); really just looking for someone who's measured and use that as a starting point.
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From: Houston, TX
Re: Offset wrist pin bushing
Sounds like a lot of work for miniscule results. General rule of thuimb for that is .035-.040" (zero deck and 1mm gasket), so I would shoot for that and concentrate on other spects of the engine that could actually net some noticeable gains.
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From: Houston, TX
Re: Offset wrist pin bushing
I've been told the exact opposite. Several different engine builders in the supercharged alcohol dragster circuit have said that they run the piston much further away from the head. Apparently they have found that running more quench makes more power, rather than running tighter quench.
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