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So I’ve decided to check the v2p clearances using the check spring method on my DOHC Honda engine. I see the pros and cons to the various methods but what I like most about this one is I can check the v2p clearance at a variety of settings without having to pull the head off a 10 times to check 10 different combinations etc...
My concern as I go through this process is v2v contact. When using this technique what is the best way to avoid this problem along the way? Should I advance both intake & exhaust and retard both together when measuring? I imagine if I (for example) checked the intake up to +10 and then left it there while checking +-10 on the exhaust this would be a bad approach. Lastly how far is really worth testing? +-10 seems more than necessary though the cam gears go to +-15 crank degrees. I’ve got a nice fixture kit specific for the engine to help with this process.
Details on the engine in case someone has a lot of experience with the same combo are:
b18c1 (GSR) w/ P72 head with Skunk2 Tuner 1 camshafts, stock USDM GSR 10:1 pistons, stock valves, crower springs & retainers, Toda cam gears marked in crank degrees rather than cam degrees.
just be careful and turn the engine over slowly. Stop of it isn't easy.
Ah, I initially misread this as a concern about valve clash, where oversized valves and big camshafts may have potential for the valves to make contact between inlet and exhaust - especially as they do flex and move a little in operation... Some of you may be familiar with engines like the older Jaguars where they actually had to redesign the head to avoid this very problem - the classic "'big valve' head, although with some race engines it isn't that unusual to alter valve spacing, or position, for greater efficiancy - Chevrolet have had several different valve angles for their race and high performance heads.
While proper practice would have one checking every cylinder, for most applications I would suggest doing a single cylinder as an initial check would suffice, with all being done if it seemed a little tighter than I would like. Different engines may need some tweaking of the process, though.
For ease, of doing the job, either just fit the piston assembly, or valves in the head for, or both, to #1 cylinder - this means you don't need to worry about valve-piston interference to any other cylinders when turning the crank or cam's. This means the camshaft/valves not being checked can be placed in the fully closed position - ~180 degrees (camshaft) from the one being tested - as a 360 revolution of the crank would bring that into testing range.
I would start with the normal installed position for the camshaft being checked, then set it/them to the full range of their travel with the piston at BDC and slowly rotate it, checking the actual V-P interference at 5 degree increments from 15 degrees BTDC to 15 after. I would just depress the valve against the spring with a finger every few degrees, though, to ensure there wasn't a sudden closure.
If you want to save some work later, especially if you're considering a later camshaft change, is to plot the available travel between the valves and the piston over a range of, say, 30 before to 30 after TDC at 2 degree increments, and then plot that travel on a graph referenced to the crankshaft. Most camshaft providers will give several checking points and even a lift @ crank angle graph, which you can transcribe to your chart to check if you have clearance.
@David, that was my theory glad it holds some water. I do have this fear of somehow the valves getting tangled between each other where they slip by each other but can’t go the other was as easily, like a kid getting their head stuck between the bars of a fence. Hopefully that’s a very unlikely scenario.
@Gord, engine already all assembled and hoping to not pull the head off. I find there is risk with every disassembly/reassembly too. For this I just have to change 4 valve springs temporarily and hoping I can do that without some sort of misadventure. Everything you said makes perfect sense in a more ideal universe. Any additional wisdom if all the valves are in? Sounds like it is worth testing up to +-15 crank degrees.