Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks
SHOP ONLINE | ONLINE CATALOG | ABOUT US
My tale of woe continues. I have driven this car around town without too many problems, however recently I took it on the freeway and found that at about 35 mph the engine started vibrating and there appeared to be a relative loss of power. In the garage I found that at about 1700 rpms the engine had the same vibration. The engine was rebuilt several years ago, and the rebuilder is no longer available. The engine has about 100 miles on it.
I have checked my fuel flow and timing advance which work properly.
In my limited knowledge of internal combustion engines I have come across articles describing the phenomena of "valve float" in which the rocker arm springs are not strong enough to close the valves at higher RPMS.
The 207 engine has two sets of springs, one on top of each tappet, and one for each valve on the rocker arm, presumably to increase the pressure when closing the valves.
In my research I found an article that indicates some rebuilders remove the springs on top of the tappets, and replace the rocker arm springs with a stronger spring, accomplishing the same tension. It turns out that my rebuilt engine does not have the lower spring (on top of the tappet), and there are two flat washers between the rocker arm pillar and the top of the head. I suspect that the rebuilder thought he could increase the spring tension on the valves by raising the entire rocker arm assembly.
I have a "parts" engine that has the lower springs. Before I take everything apart I thought I would share my suspicions with anyone reading this post to see if it is reasonable. Please let me know your thoughts.
Thanks, Steve
Steve, The 207 engine in my 34 Master ran poorly when i first acquired it. The combination of observing a vacuum gauge, and performing a leak down test, caused me to remove the head to check the condition of the valves. I found that the exhaust valves were burned and sure enough, the lifter springs were missing. It was discussed on the old forum several times, that discarding the lifter springs and not upgrading the valve springs would cause burnt valves Gene recommended replacing the valve springs with those from a 1938 and up 216. I did this several years ago and am very happy with the results. Another thing that really helped the vibration was replacement of the engine mounts.
Minetto,
Thank you for your reply, Would you recommend getting the later model springs over using the lifter springs that I have from my second engine?
I think I will do a compression test before I proceed to see if the valves are OK.
I have new motor mounts in place.
@steven-cavagnolo Steve, WOW, Washers under your rocker arm shaft supports. What the heck is going on there? You say the rebuilder is no longer available. Was he murdered by a disgruntled customer. Is he in prison for impersonating an engine rebuilder?
The only reason I can think of for washers in this location is that he used valves that were too long and had to compensate for the extra length by raising the rocker shaft assembly. If the valves are not correct for the application, who knows about the keeper location, installed spring height, etc. I never would have thought about valve float at 1700 rpm but if the spring pressure is greatly reduced by an installed height that is too tall and the lower springs have been removed, all bets are off.
I just sent a set of the lower spring parts to another forum member but I might be able to put another set together if you need them. I could also come up with a measurement from the top of the head to the top of the valve stems if that would be helpful.
Mike
Many Miles of Happy Motoring
3469 Posts on Old VCCA Chat
Mike, thanks for your reply. Yes, my rebuilder was an older cuss who probably thought cutting corners was OK. I have other stories about him that should have raised red flags, but that's water under the bridge. I guess you could say that I have learned a lot from his mistakes.
The lower springs and retainer brackets in my donor engine appear to be in good shape. Since I have the second engine in tact, I can measure the length of the valve stems for comparison. I should be able to report back tonight.
thanks again. Steve
The only time I have heard of putting washers under the stands is if a replacement head that is thinner is used. Might be a good idea to check the head casting number.
7472 old site post
The results of a compression test should help you decide the condition of the valves and seats. If possible, I’d also observe the needle on a vacuum gauge before any disassembly. With regard to recommending whether to use lifter springs, or changing to 216 springs only, I can only say I’ve been happy with the 216 spring change out. As mentioned, the old forum, which is searchable, has many threads on this topic.