duntov cam adjustment for drivablity

[Matt L.]

i was curious to valve adjustment for drivabilty on my 64 fuel injected car with the duntov cam. the car has 4:11 gears and cruises about 3500 at 65mph. it seems real happy there. the current valve adjustment is 12/18 with full roller rockers just put on this week. i had roller tip rockers in the past when all the problems occured. we are thinking the full roller rockers will relieve most of the strain that my valvetrain seems to be having.
i have been researching the archives trying to find a cure to my problem. i like to drive my car as much as i can. over the past couple years i have had problems with the adjustment backing out all together which was cured with poly locks and recently on cylinder #1 the intake screw in stud just snapped. my engine builder is a great mechanic and he has been building these engines for over 30 years. he has never seen this. we are both trying to figure this out. i have no reason to question him. i am just trying to figure this out and keep it from happening.
my engine was decked as was the heads to true them up.but i dont recall how many thousandths. the engine is 60 over. the heads had new seats cut into them and spring pockets recut? the spring pressure was within specs. i was there when he was checking that. the heads needed alot of work to save them.
could the consistent rpms not be favorable at highway speeds? i thought the 327s loved to rev and this one does.
with the heads and block being decked could the pushrods be too long now? wouldn't the adjustment on the solid cam take care of that if that was the case?

i appologize for all the questions but after having the same problem a few times, it is getting confusing for me and i would love to put my mind at ease when i'm driving.

i appreciate any advice.

take care,
matt

[Dan H.]

Re: duntov cam adjustment for drivablity

Matt, if you have a 64 you shouldn't have the Duntov cam. What motor/hp do you have? Solid cams were 30/30 in 64.
Dan

[Matt L.]

Re: duntov cam adjustment for drivablity

Matt, if you have a 64 you shouldn't have the Duntov cam. What motor/hp do you have? Solid cams were 30/30 in 64.
Dan

my builder put in the duntov cam. he said it would be more responsive than the 30/30 which was lazier on the bottom end. sorry about that. i should have explained what we did.
i have the 375HP fuel injected engine with the 375R unit.
thanks,
matt

[John D.]

Re: duntov cam adjustment for drivablity

HI Matt, It's a wonder your engine builder didn't push the LT1 cam . I see your posted late last night.
By the way the 097 cam and the 375R go well together. Now the spring in your enrichment diaphragm cover (if stock) would be for the 30-30 cam. But that wonm't hurt anything and may even help if your vacuum is a tad low.
Good luck on solving your problem. JD

[Matt L.]

Re: duntov cam adjustment for drivablity

hi John, the car runs great. it really gets going in a hurry. i have no problem with acceleration. its just this pesky problem with the rockers. i'm going to drive it all week and put some miles on it in hopes that the full roller rockers cure the problem. i want to drive this to the expo again this weekend. last year when i driving there was when the rockers backed off.

take care,
matt

[Joe R.]

Re: duntov cam adjustment for drivablity

Matt,

The rocker studs in your heads are probably worn out but the poly locks will treat that problem as they don't rely on the threads to keep them tight. To permantly fix your problem, I would recommend screw in studs, poly locks and roller rockers. I don't trust the studs in a 50 year old head that were just pressed in to begin with at the factory.
Your engine builder gives good advise when he said to get rid of the 30/30 camshaft. It's a dog just like the LT-1 camshaft! There should be a law passed prohibiting the manufacturing of those camshafts. Yes Duke, a law!!!!
Come by and visit me this weekend at Corvette Expo. I would like to see your FI 64 Corvette!!

JR

[Timothy B.]

Re: duntov cam adjustment for drivablity

Matt,

I think you should pay attention to rocker arm geometry, if the block and heads have been broached the pushrod length is probably to long. The test for this is to bring the valve to exactly half lift and see that the rocker/valve stem relationship is in the center of the rocker arm radius.

Poor rocker arm geometry can cause studs to break and wear valve guides because the rocker pushes the valve stem against the guide. Valve spring installed height and spring pressure can also cause problems and with your 411 rear you are always up inthe rpm range. Shorter pushrods are available to solve the rocker geometry and IMO that's where I would look first.

Joe Ray, I don't consider any camshaft factory installed as a dog, I agree the Duntov is a good cam but the 30/30 with a 411 rear has got to run good. We have enough laws in this country. :-)

[Duke W.]

Re: duntov cam adjustment for drivablity

Matt,

It's a dog just like the LT-1 camshaft! There should be a law passed prohibiting the manufacturing of those camshafts. Yes Duke, a law!!!!
JR

Being as how the LT-1 cam uses the L-72 lobe on the inlet side, I guess you'll have to "outlaw" the L-72 cam, too.

Duke

[Duke W.]

Re: duntov cam adjustment for drivablity

ihaving.

the spring pressure was within specs. i was there when he was checking that. the heads needed alot of work to save them.

How do you know? For one thing, valve springs don't exert "pressure". They exert force. What are the specs? What is the manufacturer and part number of the springs? For that matter, what is the manufacturer/part number of the cam?

On 461 heads the pushrod holes in the heads act as pushrod guides. Have they been opened up?

Even with head and block milling, I don't think the rocker geometry would get out of whack with a true Duntov cam because it has so little lift, but add to the above significantly sunk valve seats and you may need shorter pushrods.

Clearly you have a problem in the valve train, so the first thing to do is "audit" the installed parts, then look for geometry issues.

Duke

[Clem Z.]

Re: duntov cam adjustment for drivablity

you don't need to elongate the push rod holes in the heads unless you go to the 1.6 rocker arms.

[Matt L.]

Re: duntov cam adjustment for drivablity

hi everyone,
the heads have all new guts. screw in studs and all. the pushrods show no wear from rubbing the holes. the 1st setup was 1.5 roller tip rockers with factory nuts. then i had problems with the nuts backing off. we then went to polylocks and that solved that problem. our new problem is broken screw in studs which are arp. this has happened twice on the same cylinder #1. one exhaust and one intake. the cam is exact duntov specs. my engine builder had some made. my engine builder is a machinist by trade. so i cant see him not checking and double checking all the specs. we even talked about the geometry being off due do all the milling. he is confident that is not the problem. we now have full roller rockers installed this past weekend. the engine runs great and always has. it free revs with no effort especially now with the full rollers. i have all the confidence in the world for my engine builder. he has over 30 years experience with these engines and fuel injection.
the valves do sit down in the heads due do recutting the seats. could this be where the problem is?
Duke, i dont have any specs on anything in front of me. i do like your thoughts on the sunken valves. if this problem persists i will ask for shorter pushrods. my thinking was since it's a solid cam you can adjust for the variance unlike when a hydraulic pumps up fully then you would have clearance issues. i made that mistake on a pontiac engine i built by myself. 455 heads valves are .25 shorter than 400 heads valves. idled fine then all hell literally broke loose on the gas. bent valves and pushrods.

Ray, i will make sure to stop and see you this year. i was in a fog last year when i was down there because thats when i had my 1st problems with my car. ask my wife, i cant think straight when something is wrong with my kids or cars.

thanks you everyone for all the great advice.

take care,
matt

[Duke W.]

Re: duntov cam adjustment for drivablity

hi everyone,
my thinking was since it's a solid cam you can adjust for the variance unlike when a hydraulic pumps up fully then you would have clearance issues.

Valve clearance adjustment, which is in a very small range has no significant impact on fundamental valve train geometry.

Something is putting a big bending load on the rocker studs. That's why they break. An example would be a high lift cam and a rocker with too short a slot that causes the rocker to bottom out against the stud at full lift, but a significant deviation from OE rocker geometry due to excessive head/block milling or excessively sunk valves could cause the same problem even with OE components, however, if you have roller trunnion rockers this shouldn't be an issue unless the rocker is limited in its rotational travel.

A shorter pushrod will usually help, but it may also require shortening the valve stems; however, there's a limit as to how much can be removed because the tip is hardened, and it also has to stand clear of the retainer. Multiple valve grinds can sink the valves so much that the only choice is to install seat inserts or scrap the head.

Duke

[Matt L.]

Re: duntov cam adjustment for drivablity

[QUOTE=Duke Williams (22045);605521]Valve clearance adjustment, which is in a very small range has no significant impact on fundamental valve train geometry.

Something is putting a big bending load on the rocker studs. That's why they break. An example would be a high lift cam and a rocker with too short a slot that causes the rocker to bottom out against the stud at full lift, but a significant deviation from OE rocker geometry due to excessive head/block milling or excessively sunk valves could cause the same problem even with OE components, however, if you have roller trunnion rockers this shouldn't be an issue unless the rocker is limited in its rotational travel.

thanks Duke for taking time to explain. i understand now. i am on the same page with you concerning the valve seating being too far in the head. the head machinist warned of cutting into the water jackets...thats how deep in the head the valves are. i questioned the compression loss due to the valve seating. unfortunatley, i have a ton of money in these heads as you can imagine with all the work they needed.i am going to see if the new rockers will fix the problem. and if not maybe try shorter pushrods as a last resort.
Duke, in your opinion, does the highway travel rpm speed at 3500 have a good or bad effect on a well balanced and built engine? other than this problem and perculation issues, the engine has been perfect. it was balanced when built early last year.

thanks again everyone,
matt

[Clem Z.]

Re: duntov cam adjustment for drivablity

i drove many miles with 4:11 rear gears in my corvettes and Z-28 camaros with no engine problem from extended RPMs. drove to Fla and Myrtle Beach many times from Pa.

[Matt L.]

Re: duntov cam adjustment for drivablity

i drove many miles with 4:11 rear gears in my corvettes and Z-28 camaros with no engine problem from extended RPMs. drove to Fla and Myrtle Beach many times from Pa.

thats what i want to do with my car. i want to drive it. i think the engine doesnt know if its running 2000 rpms or 3500 rpms. the parts are just turning faster. as long as it stays cool with good oil pressure there should be no issues. they drove these cars when they were new...why not now? i get that question all the time..."you drove this here,all the way?" i always reply the same" why not? they drove them when new"

take care,
matt