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Author Topic:   How can I .......
RC Racing
Member
posted July 15, 2003 12:33 AM
add shims to my valve springs without pulling the heads?

I'm running 450 lift cam (don't remember the duration), cast 4-valve relief on 76 cc heads with 1.94/1.50 valves, hyraulic lifters, springs are stock diameter 130#, 1.5 long slot rockers, guide plates, Q-jet.
(enough info I hope)

I may have 80 laps on this new motor. Last weekend I noticed a high rpm miss (spun her up to 7400 rpm, but don't plan on doing that too often!) Pulled the valve covers, checked a few springs and they were all over the place (anywhere from 95 to 120#s).

So I thought I would shim them to get them evened out.

So I have 2 questions:
1) Does it seem to you like the springs life was a little too short? I've heard the cams are hard on these relatively stock valve trains, but still... Is this the life span I should expect?

2) If so, instead of replacing sprngs about once a month, I thought I would shim them. But I'm not sure how to go about doing it without removing the heads. So I'm looking for tip, advice, shortcuts, etc..... Can I just turn the motor so has to have the piston near or at TDC, and then remove that cylinder's springs (logic is that the piston shold be up high enough to keep the valve from dropping). Will that work or is there a better method?

Appreciate everyone's help.

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BK19
Member
posted July 15, 2003 05:47 AM
you need to fill the cylinder with air pressure then use the spring tool they make for this purpose


Ryan Lingner
Member
posted July 15, 2003 10:45 AM
Sounds like the springs are gone to me. A shim isn't the answer. YEs you will increase seat pressure but will also reduce space between the coils and might run into coil bind. Assuming the heads had been set up correctly to start with and spring height set correctly then the opnly answer is the springs are bad unless the seats have moved. What is your insaleed height now? What spring are you using?


sdhnc29
Member
posted July 15, 2003 02:43 PM
I would change springs to be on the safe side . One thing that was probably overlooked when the heads were set up originally , is to compress each spring completely in a vise before trying to set up your spring pressure . It is very common for most springs to lose 10-20lbs , depending on the brand and quality , after you compress them in a vise for 3-5 minutes . Many people will simply check the spring pressure right out of the box and install them if their seat and open pressure is correct . This is a BIG mistake ! Essentially you could think that you have 130 on the seat , and soon after start up have only 110 lbs on the seat and be even worse off on open pressure .

What I mentioned above might be part of your spring pressure problem . I would also look at the spring tester that your using since many of them are not accurate . So to summarize , I would still replace all of your springs to be on the safe side , and simply compress each spring for 3-5 minutes , and then set up your heads .

Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


RC Racing
Member
posted July 15, 2003 04:57 PM
After a little thought abased on y'alls responses and input from others, I have decided to replace the springs.

And I gues if I'm going to have to do this about every 100 laps, I better learn how to do it properly. (talked with my engine builder & he confirmed what others have said, these spings are long lasting)

Steve, you said I should "set up my heads". Would you (or anyone else knowledgable in this area) elaborate on what you mean? And are there any recommended job specific tools I should invest in for this (once again, 'cuz it looks like I'm going to be doing this on a regular basis)

Thanks all

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RC Racing
Member
posted July 15, 2003 05:00 PM
Sorry Ryan, forgot to respond to your ?s

To your 1st question, I don't know the installed height? And I forgot to ask the engine builder when I talked to him earlier today.

To your 2nd question,I'm going to buy a new set of Comp 941s.

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RC Racing
Member
posted July 15, 2003 05:02 PM
(gotta start proof reading this stuff before I post my reply)

Correction: engine builder said these springs are NOT long lasting.

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Ryan Lingner
Member
posted July 15, 2003 07:59 PM
A spring height gauge is nice. Summit sells one. IT's basically an inside mic designed just for checking the installed height of springs to put it simple. JUst buying an aftermarket set of springs doesn't finish the job. All these spring are rated at a certain installed height to have the correct open and closed seat pressures. LEts say you have had a few valve jobs done over the years on the heads or at least somone has. Each time you cut the seat and gring the face of the valve you increase installed height and need to correct that.
Steve has a very good point as I always destress the spring in a vice. I've seen big time changes and others not much so always good to do this on every new spring change. I've even tried to pre heat the springs in the old kitchen oven,ha. Wife was far from happy so I think I would skip that,ha.


rico 08
Member
posted July 16, 2003 07:11 PM
Valve float is extremely hard on springs,and sometimes the engine will float at a lower rpm every time you float them.130# seems like alot for a stock dia spring,i wouldn't think they would hold that for too long.


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