cam specs?
01-27-2002, 11:26 PM
#1
Charter Member
cam specs?
Have the Crane 139741 cam now and looks like I may have to replace it, after only 40hrs. $700 
It ran great last summer, so may just replace it. But also highly considering the Crane 139731 cam. From what I understand in the BBC marine book, the xxx31 is actually a better choice. The less duration is the reasoning. More duration is for higher CR & higher rpm motors with better intake and exhaust efficiency. I just don't understand if my blower changes the cam recommendation.
My motor is a HP465 w/B&M 250 @ 5# boost.
Original 8.75 pistons. Rect port heads that with work on both intake and exhaust sides. Merc/Gil exhaust with silent choice with no reversion problems. Been turning up to 5800 rpm, going to limit that to 5200 now.
Cam specs are:
139741
.610/.632 lift, .234/.242 duration
139731
.587/.610 lift, .226/.234 duration.
(This one is just a step up from the HP500)
Any advise or comments would be greatly appreciated pertaining to these 2 cams.
The reason for the replacement is that with my cold running motor, I had so much condensation that the moisture/water would rest on the contact point of the lifters and cam on the cyls. 7 & 8 during the week, that it has discolored both cam and lifters at those points. I can feel some difference on the roller lifters, none on the cam at the discoloration points with my fingernail. Have thought of just replacing the lifters and polishing the cam. Is that a possibility?
Anyways, Thanks
Jerry
[ 01-27-2002: Message edited by: US1 Fountain ]
It ran great last summer, so may just replace it. But also highly considering the Crane 139731 cam. From what I understand in the BBC marine book, the xxx31 is actually a better choice. The less duration is the reasoning. More duration is for higher CR & higher rpm motors with better intake and exhaust efficiency. I just don't understand if my blower changes the cam recommendation.
My motor is a HP465 w/B&M 250 @ 5# boost.
Original 8.75 pistons. Rect port heads that with work on both intake and exhaust sides. Merc/Gil exhaust with silent choice with no reversion problems. Been turning up to 5800 rpm, going to limit that to 5200 now.
Cam specs are:
139741
.610/.632 lift, .234/.242 duration
139731
.587/.610 lift, .226/.234 duration.
(This one is just a step up from the HP500)
Any advise or comments would be greatly appreciated pertaining to these 2 cams.
The reason for the replacement is that with my cold running motor, I had so much condensation that the moisture/water would rest on the contact point of the lifters and cam on the cyls. 7 & 8 during the week, that it has discolored both cam and lifters at those points. I can feel some difference on the roller lifters, none on the cam at the discoloration points with my fingernail. Have thought of just replacing the lifters and polishing the cam. Is that a possibility?
Anyways, Thanks
Jerry
[ 01-27-2002: Message edited by: US1 Fountain ]
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Some people are like Slinkies - Not really good for anything, but they
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Some people are like Slinkies - Not really good for anything, but they
bring a smile to your face when pushed down the stairs.
