460 Head and Cam Upgrade Help

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460 Head and Cam Upgrade Help Empty 460 Head and Cam Upgrade Help

Post  Kyeroc on March 25th 2019, 3:11 pm

Hi guys.  I am new to the BBF world and helping my young son do some upgrades to an old jet boat he is going to run at the lake this summer.  The boat currently has a Hardin Marine 460 from about the 1978 vintage.  Motor is all stock with D3VE heads, factory cast 21cc dished pistons (assumption), but runs a tunnel ram, dual 4s and Bassett headers.  The guy we got the boat from said the motor was just "freshened".  We have somewhat verified that with a static compression test and the fact that it has good oil pressure.  Plan was to simply pull the heads and replace with the early style heads, adjustable valve train, upgrade the cam a bit, and correct the cam timing.  This is a 40 year old, beat up old boat that is supposed to be a low budget project.

Things got a bit more complicated though when we could not find a decent set of small chamber heads on the cheap.  We did finally find a set of C9VEs locally for almost nothing that came off an old race motor.  They actually have been completely gone through and have sat in a shop for years.  We have disassembled these heads and they are in fact as new.  The heads have 2.25" intake valves, 1.75" exhaust valves, screw in studs, guide plates, and all the machining has been done to clearance for high lift cam and dual valve spring setup.  Heads have been ported and according to the guy we got them from were basically worked over to match a set of CJ heads.  From what we can tell, the Weiand tunnel ram and Bassett headers will work with these heads.  Whatever these heads are, I know for a fact they are way too much head for what we are doing.  However, since the heads are basically brand new, we want to try and make them work if possible.

So, this is where I am hoping somebody can chime in with some advice.  We want to run the C9VE heads outlined above with a Comp Cams XE274H cam that we picked up.  We have searched and read and it appears that valve/piston clearance might be an issue with the oversize valves.  Detailed cam and head specs outlined below:

CAM SPECS
Comp Cams XE274H
Duration@.050 = 230 intake and 236 exhaust
Lift = .562 intake and .565 exhaust
LSA = 110
Intake centerline = 106*

ADDITIONAL HEAD SPECS (as measured with digital caliper)
Installed spring height = 1.9"
Clearance between top of seal and bottom of spring retainer = .870"
Intake valve length = 5.28"
Intake valve diameter = 2.244"
Exhaust valve length = 5.04"
Exhaust valve diameter = 1.744"
Distance between seated valves = +/-0.075"

Hopefully the above is enough info to get started and help us figure out if we should continue down this path and pull the original heads.  If we have to go down the path of changing pistons (we are willing to cut the pistons in the block if the stock dished pistons can be modified to work), we may just abandon this plan and figure out a different route.  Any help, advice, feedback you guys can offer in regards to valve/piston clearance issues with this combo would be much appreciated.  Thanks.

Kyeroc

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Join date : 2019-03-25

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Post  rmcomprandy on March 25th 2019, 11:15 pm

Be sure to check the valve notches in those pistons to be positive that they are large enough in diameter for the larger diameter intake valves in the heads.   If it is a cast piston, I don't believe they will be big enough, deep enough though.

rmcomprandy

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Post  Kyeroc on March 25th 2019, 11:59 pm

Thanks rmcomprandy. If the valve reliefs are not large enough radially, is it safe to fly cut the reliefs in the stock cast pistons larger to accommodate the larger valves?  I was thinking if I had to I could rig up a 2.30” intake valve as a tool and cut them larger while still in the engine, using the head as the guide.

Is there any chance the exhaust will be close enough to also require clearancing with the cam/head selection or is exhaust valve most likely clear because of the cam timing?

Thanks again for the info.

Kyeroc

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Post  rmcomprandy on March 26th 2019, 9:54 am

Kyeroc wrote:Thanks rmcomprandy. If the valve reliefs are not large enough radially, is it safe to fly cut the reliefs in the stock cast pistons larger to accommodate the larger valves?  I was thinking if I had to I could rig up a 2.30” intake valve as a tool and cut them larger while still in the engine, using the head as the guide.

Is there any chance the exhaust will be close enough to also require clearancing with the cam/head selection or is exhaust valve most likely clear because of the cam timing?

Thanks again for the info.

Usually ... it really depends upon the top ring location down from the crown of the piston;
O.E.M. pistons are probably no problem.

The exhaust valve should be far away as is because that valve is farther up in the head.

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Post  Kyeroc on March 27th 2019, 10:22 pm

Ok. Made some good progress today. Installed cam at spec'd 105*/106* intake centerline. Test fit the head without a head gasket, took a bunch of measurements and tested valve/piston intersection using some grease on the bottom of the valve. The intake valve actually sat completely down in the valve relief of the stock dish pistons. Based on the measurements, some math and the fact that the valve sat all the way down in the relief, we were pretty comfortable that the valve would not hit the piston once assembled. Moved on to partially assemble and clay valve/piston clearance. It looks like we have .130 clearance on the intake valve, which sounds pretty good to a completely inexperienced guy. Please let me know if this is wrong.

Upon inspecting the valve train once setup, it is clear the geometry is not perfect. The tip of the roller rockers do not ride in the center of the valve stem. They are not off of center from a pushrod length standpoint, the tip of the roller rocker actually rides off center towards the exhaust valve (roughy 3/4 of the roller tip is riding on the valve stem tip). We have done some searching/reading and it seems like this is sometimes a problem and some guys say run it, others say that the push rod guide plates need to be cut, moved around and welded back together to get the tip of the roller rocker centered on the tip of the valve stem. I would rather just run it if it will stay together and be OK in this mild application. By the way, we are using a set of "free fifty free" BBC 1.7 ratio roller rockers. I am not sure of the brand.

Again, just looking for confirmation on the piston/valve clearance and any insight anybody wants to share on the off centered roller rocker issue. Thanks in advance for the help.


Kyeroc

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