Valve Springs

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Would there be any issues caused by doubling the stock valve spring pressure? I am considering installing stock Chevrolet valve springs in a 125ci engine. 

Edited by PaulB - 17 Jun 2016 at 1:18pm

Thank you Paul for the useful information and posting a picture of your turbo set-up. I had been wanting to see how you plumbed the draw-through system, She sure walks that sled LOL.

Well, parts came in yesterday so I made a trip into town to go over what I wanted done to the head. The exhaust seats were ate up a lot worse than pictures show. Before I bought it, it had set outside in the rain, probably for years. Although the exhaust was capped water runs in around the exhaust pipe adapter sleeve at the manifold. The shop where I took the head has a Serti machine, he showed me how deep he would have to cut the worse exhaust seat to clean up the pitting. So we stepped back in his air conditioned office where we could think a little clearer. He knows this tractor and has rebuilt dozens of these heads, he doesn't think I'm doing anything unusual or extreme. He made me a cash deal on hardened exhaust seats installed and 3-angle Serti cut. The intakes seats didn't need a lot of material removed to clean up like the exhausts.

I did ask him about valve springs and showed him the stock and Chevrolet springs. He checked the rate of the chevy spring and said it was a 45lbs rate spring, wouldn't hurt the stock valve train at all. Didn't add anything more to his reply.

All I can do is offer my opinion why I feel this engine would respond positively to higher rate valve springs. I wish Jerry had checked the rate of the new stock spring but it didn't seem important at the time.

First I considered all the weight that the spring has to over-come. Valve, retainer, keeper,  rocker arm, pushrod and lifter. The valve spring has to control the weight of those items to follow the cam lobe profile. I understand we are discussing a low rpm engine but those stock springs look marginal at best for maintaining valve-train control. I'm going to say that 45lbs of seat pressure should be required as an upgrade to seal the valve on the seat for reliable compression. That's not carved in granite though. There are some very knowledgeable engine builders on this forum that may be holding a different opinion.    

Hundreds of thousands of those engines built and you think it needs more valve seat pressure????

The Engineer(s) who designed the valve train on this engine series(which would include the valve springs) had to meet several criteria before settling in on the final design. Now, I wasn't there, but I imagine I can guess what some of those criteria were. #1. Performance #2. RELIABILITY   #3. cost #4. Serviceability #5. service life. To just decide to increase spring pressures without proper testing of the rest of the components, would automatically create at least one negative...lack of performance. By that I mean, increasing spring pressure on all eight valve springs (when it isn't needed) would certainly not result in an engine HP increase. Quite the contrary...it would create more friction on all parts involved and quite possibly result is less HP/torque produced at the flywheel. How much?? Depends on the increase in spring pressure, but one thing for sure.....it wouldn't cause a gain in HP !! Then, there's the matter of service life. Cold starts with little oil to lube the camshaft lobes and lifter faces, etc, etc. Yes, all of those nasty little details that one change in design specs can come back and create unforeseen problems to the life span of other related parts. You go right on ahead and do what you want to do. But, always remember there were millions of those springs used over the last 70 years that have never caused one second of downtime over millions of hrs of service life AND were often reused time and time again at overhauls and placed back into service, and they still performed well not ever causing a problem..

The valve spring p/n is 70206879 for the B-C or CA tractor engine. It also is used on the D-14 and D-17 engines. Those are 2,000 RPM factory speed engines. I have used stock valve springs at 3,000 RPM when tractor pulling and have never floated a valve or had a push rod jump out of place. I sure hope you find someone who is knowledgeable about these AC engines to help you figure out valve spring pressures are good enough as-is.

Edited by Ryan59 - 04 Jul 2016 at 2:39am

Edited by Ryan59 - 04 Jul 2016 at 2:33am

Edited by Ryan59 - 04 Jul 2016 at 2:31am

Valve spring pressure increase has more to think about than RPMs, when you are dealing with turbo boost pressures. As the valves have to close against that flow pressures also.  

Change of thought here Ryan, you said you worked at Boeing. Was that in St Louis?

Ryan the way I see it you have made your mind up to do this regardless of what several people have tried to give you reasons not to ,you keep trying to justify this to us it's you tractor fix it the way you want and have a great day

I see spanky series 2 has weighed in...  Now you know...