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How much did you have them take off the head at the shop? Isn't normal CR about 9:1?? What year valve springs did you use? are there different tensions as the years increase? I will probably be doing this same thing in about 3-4 years (maybe sooner)...just want to get it running for now..
1988 n/a engine (north american) cr: 10.2:1
30 thousandths machines off bottom, to be used with standard gasket.
Some say that makes it 11:1 others say as low as 10.65:1.
I'd get more removed if I didn't run the lumpier camshaft. Life's full of compromises
Valve springs: I'll no longer purchase regular valve springs. Turbo valve springs are where its at if you are rev happy.
Did you know your valve springs lose pressure from the moment they are installed on the engine? And even sitting in an engine in storage they loose performance. Why not install a stronger spring from the start?
THINGS I DID RIGHT today: used a head gasket (old 1.4mm thick one). used only enough clay to fill the piston reliefs, applied generous amounts of engine assembly lube on the top of the clay (but not the bottom) so it wouldn't stick to the head or valves. This photo shows block after wiped off lube & very carefully cut off half of the intake relief clay with a razor.
THINGS I DID WRONG yesturday:
-performed test without a head gasket & used WAY too much modelling clay (for this engine), and didn't oil or grease the top of the clay. So the result was a mess.
So, with a seven degree cam advance & a head gasket thats about 10 thou thicker than I plan on using, here are the results:
The engine CAN be rotated by hand, but would surely blow up under running conditions.
The exhaust valve barely even kisses the clay. I measured it for fun by stabbing the sliding rod out of the digital caliper; measures about .100" (1 tenth of an inch). The intake valve was really a concern however & I wanted to very accurately measure. Using a fresh razor I cut & removed half the clay, being careful not to distort (it's ubber soft). Measured about .024 -.030" (lets call it 27 thou).
So what's going on & how to correct it?
Well the first question is why an indentation on the intake side but not the exhaust?
Answer: cam advance. 4 stroke engine (suck/squeeze/bang/blow). I *think* the intake is simply to close to the piston .
Correct: retard. I think I'll advance the cam 2 degrees instead of 7.
But how much difference will that make? Also the reality is I want to use a thinner head gasket, so even with the reduction in advance, will I still not have enough piston clearance?
Chances are I will be still needing clearance.
Solution: thicker head gasket?
Return to use the other Jon Milledge cam with less lift/different profile.
Good questions & good points made H.F.B.! Also, thank you for including the list.... if you don't mind I'll keep a copy of that for my records.
I wanted to advance the timing for more power earlier in the rpms. 7 degrees sound like a lot, but if you consider that shaving the head retards the timing... so really we are back to what 4 degrees advance?
Regarding the thicker gasket as a solution for clearance. I merely listed that as a solution to assist with the valve clearance, not what I actually want to do). Sorry for confusing things.
Valve to piston clearance change is non-linear in that small amounts of cam advance/retard can result in drastic difference in measured clearance due to relative piston position during the open/close ramp profile. I usually look at adjustable cam gears as being useful for helping to dial in clearances on a fresh engine rebuild where some deck height is lost rather than being a tool to dial in arbitrary amounts of advance at whim.
I would suggest claying the engine with the cam gear indexed to 'zero', and seeing what measurement you get. Go with what makes the engine mechanically happy.
Okay... please give me the strength to get 'er done & back on the road this weekend. Really feels like I've been spinning my wheels & not progressing. >
Valve to piston clearance change is non-linear in that small amounts of cam advance/retard can result in drastic difference in measured clearance due to relative piston position during the open/close ramp profile. I usually look at adjustable cam gears as being useful for helping to dial in clearances on a fresh engine rebuild where some deck height is lost rather than being a tool to dial in arbitrary amounts of advance at whim.
I would suggest claying the engine with the cam gear indexed to 'zero', and seeing what measurement you get. Go with what makes the engine mechanically happy.
I shoulda listened but thought I knew better.
Todays results shocked me. Was disappointed at first.
Thought I was good as gold if I reduced the advance to 4 degrees & installed the "old" cam, this one: http://jonmilledgeengineering.com/product/s3-14/.
Results are in:
Not enough clearance on the intake valve side. Didn't even mark the clay on the exhaust & the intake clay measure .030" (even with the thicker 1.4mm gasket). Basically the SAME as the much higher lift cam.
...and so the saga continues. Man this is boring and lame. This CONFIRMS what Ohio Tom was saying. Valve clearance is not so much an issue of overall lift, it's duration that kills engines.
Oh lucky day! On at least 2 other accounts since owning this car I have had to reinstall the cam housing & timing belt just to remove the cam sprocket in order to pull the cam out. Today I tried something on the bench & it worked to remove as well as torque the the cam sprocket to 50 lbsft.
By using a threaded hole in the back of the timing belt housing I threaded in a bolt & it aligns inbetween sprocket teeth & then uses a big "thumb wrench) & ratchet. It works.
Alright with big cam and no cam advance or retard. Zero impression in the intake clay and small indent on exhaust. Measure .050" with 1.4mm gasket. Getting closer. If I could advance like 1 degree... Sorry, this must be very boring for everyone, but if I don't document than things get lost.
07-04-2015, 06:05 PM
