Valve Clearance on Larger Camshaft and Flat Top Pistons

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famous bob said:
you must be ---- , depth gage works , dial caliper if your carefull , not rocket science never met anyone that couldn't do it right ... must be on you ...
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OK Bob. I'll accept that. It must be on me. My experience was from probably 20+ years ago and I think I was trying to use a dial caliper. I guess my technique was not good. Anyway, I learned a few things from this thread and it's all good. Thanks.
 
Fish Bite said:
I'll start by saying I understand that valve clearance has many variables tied up in the camshaft profile, camshaft advance, gasket, pistons, etc. and that the only way to know for sure is to measure when mocking up the engine. I will check clearance with a dial indicator when the time comes, but I'm in the planning stage and am hoping to get an idea from anyone who has experience running larger camshafts with flat top pistons.

My concern is that if I buy flat tops and end up needing to cut the reliefs deeper, I will need domed pistons to make up for the lost cc's from the deeper reliefs to stay at the desired dynamic compression. With the way timing goes at my machinist's, I'd likely be outside of the return window for the flat top pistons by the time I buy them, give them to him for his bore/hone work, and he gives me the bored/honed block for mock-up before zero-decking it and balancing the rotating assembly. Then I'm in a situation where I would have to eat the flat tops, buy domed, and now the engine is honed to the flat tops whereas the domed might need a different hone setup.

Here are my current build plans:
-360 0.030" over
-Zero-decked
-Trick Flow heads with 2.02"/1.57" valves and 1.5:1 Harland Sharp rocker arms
-Head gasket of 0.050" is ideal for the desired dynamic compression with the the Trick Flow chambers and cam profile
-The mechanical roller cam I am looking to use is 0.640" valve lift, 283/289 advertised duration, LSA 106, intake centerline 102
-The pistons I'm looking at are forged RaceTec 1000549 flat tops with two valve reliefs. I spoke to RaceTec providing them with the build specs and asking for their input on clearance hoping they had modeling software, and the only thing they told me was that the reliefs are 0.250" deep.

Does anyone have experience with valve clearance using flat top pistons with a similar combination? What's the biggest mechanical roller profile you've been able to pull off with flat tops?
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You're over thinking this. Talk to your machinist. J.Rob
 
Fish Bite said:
Thanks. Duration at 0.050": Intake 251°, exhaust 257°.
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That looks like a "Mutha Thumpr" garbage grind almost. Those cams are very inefficient. I know its not a CompCam but it looks like it--must have a very late closing exhaust for "that sound". J.Rob
 
Bewy said:
When using solid roller lifters, here is a veeeery easy way to check V to P clearance. If you anticipate that you have plenty of V to P clearance, then assemble the engine with the springs you intend to use. Easier with two people. Adjust valve lash & rotate engine until the cyl to be tested is at TDC, on overlap. Simply get a pair vice grips or multigrips & lever up on the prod side of the rocker to push the valve down until it touches the piston. The valve travel is your V to P clearance. When clearance gets tight, you need to check a few degrees before TDC on the exh valve & a few degrees after TDC on the intake valve. You can set up a dial gauge to take the measurement, but I just use a vernier caliper.
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It's usually 10 degrees BTDC/ATDC where the valves are in overlap usually about .100-.110" valve lift. J.Rob
 
RAMM said:
That looks like a "Mutha Thumpr" garbage grind almost. Those cams are very inefficient. I know its not a CompCam but it looks like it--must have a very late closing exhaust for "that sound". J.Rob
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The OP’s cam is a .425” lobe lift solid roller.
The 251/257-106 looks normal enough to me.

(It appears to be a Howard’s 711013-06.
Advertised duration is 283/289. Recommended c/l of 102/110.
That would put the exhaust closing point at 34.5atdc.)

I think this is a situation where two people look at the same thing…….but “see” different things.

RAMM looked at those specs and to him it seemed like a Thumper type grind.
I looked at the specs and to me it’s a normal bracket race type grind.
 
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Valman said:
That’s where I ended up on my current engine. - 0.036’’. I’d like to go tighter, closer to 0.030’’.
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You got it brutha! I'm .005 out with .039 gasket. Brings my quench to .034. I wouldn't go any tighter. I think .030 might be pushing the envelope.......Maybe.
 
Ironmike said:
You got it brutha! I'm .005 out with .039 gasket. Brings my quench to .034. I wouldn't go any tighter. I think .030 might be pushing the envelope.......Maybe.
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It’s the way to go! I’m at 0.003’’ out of the hole. Got to check all clearances carefully, the pistons won’t hit the head if you don’t go crazy with bore clearance.

There’s plenty of single cylinder motorcycles with a 100mm plus bore that have around 0.025’’ - 0.032’’ P/H clearance. I’d be a bit nervous under 0.030’’ I’ll admit..
 
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