cam break in

[Splitpin]

Comp cams recommend that if using valves with double springs you should remove one for the initial 30 min break in.This means having to reinstall the second spring with the heads on. Where can I get a heads on valve spring compressor that will fit a chevy? Do you have to pressure the cylinder with air to keep the valves shut?
cheers
Mike

[neil still building it]

hi
if you go to your local 'factors' and ask for a lazer tools catalogue to look through you'll see they sell an adapter to use and airline to pressurise the valves shut at 'top dead centre',then using another tool they list you can compress the spring to remove /refit the springs as installed on the engine (hopefully)as you have no other option this will have to work...
good luck
NEIL

[ian]

Mike, what cam are you fitting? I am breaking in a Comp Cams hydraulic cam on Saturday, I bought the complete kit with springs, retainers etc. (XE274H.)
When I opened the kit I thought I had double valve springs for a moment, but the inner ones are just dampers and don't exert any pressure, so I don't have to remove them luckily. Just thought maybe your situation was the same, if not then ignore me! Good luck. Ian

[TonyD]

I have been told about an old mechanics trick of feeding rope into the cylinders through the spark plug hole until the valves are supported by the bundle of rope inside the cylinder. Put the springs on, pull out the rope move onto next cylinder. Seems possible but have never tried it myself.....

Cheers,

Tony

[Splitpin]

Its an xe274, the heads will be AFR when they eventually get here. These come with double valve springs.
Heres a link to what the guys in the states say, with a couple a pictures .

http://www.chevytalk.org/threads/sho...page/0#1179754

Mike

[Clarkson]

Hi Ian,

Let me know how you get on, on sat! It looks like we are all building the same engine:thumb:

Originally Posted by ian

Mike, what cam are you fitting? I am breaking in a Comp Cams hydraulic cam on Saturday, I bought the complete kit with springs, retainers etc. (XE274H.)
When I opened the kit I thought I had double valve springs for a moment, but the inner ones are just dampers and don't exert any pressure, so I don't have to remove them luckily. Just thought maybe your situation was the same, if not then ignore me! Good luck. Ian

[ian]

Well, the engine fired up within 3 seconds so that was a relief. I had used an oil pump primer to get some oil around the engine which probably helped. It was quite nerve racking I have to say because the night before I had read dozens of reports of Comp Cams wiping lobes during break in!!! Anyway, it went fine, I ran it between 2000 and 2500 rpm for 30 minutes. I have 10:1 CR with Sportsman 2 heads so it really got quite hot, hotter than it would have done with the old cam/heads. I checked the oil (not full of metal) and all is OK. I will probably run it for a couple of hundred miles before changing (rest of engine hadn't been touched.) Only tip I would give is have someone around to help you - I didn't, so I couldn't adjust dizzy position or mixture screws to enable smoother running during break in, and I had to keep on stretching over the windscreen to see if all was OK in the engine bay while keeping my foot on the juice. I had put some mew headers on which produced loads of smoke as their paint burnt off. Have a hosepipe and fire extinguisher immediately at hand just in case. Took it for a burn last night, about 20 miles, I'm still f***ing laughing my socks off - it sounds even louder than ever (didn't think that was possible!), and it revs so much faster and easier. I still have some tuning to do but it is VERY much faster than before, easily breaks traction (with 295s on rear wheels) so caution is recommended
Oh, and the sound of the idle is awesome, sounds like a top fuel dragster. Good luck with your builds. Ian
PS By the way split pin, my XE274H kit came with single valve sptings fitted with dampers, look like doubles but aren't. Comp part # 981-16.

[ian]

Hi Splitpin, I have just re-read your post - I guess you're buying your heads assembled with valves and springs? If so it might be an idea to check the spring rate (of the dual springs when both are fitted) and comparing them to Comp Cams recommendations. I know weak springs are bad but I suspect you can overdo spring strength aswell. Of course you may have already done this and found all to be within limits. You'll really like the XE274 cam. I found that low down torque hasn't really suffered at all and you get a massive surge of torque from around 2500 rpm, and a kick in the a*** from 4000 upwards. Very rewarding, sounds really crisp aswell. Here I go again... hope it's dry this evening so I can make my rear tyres a bit lighter. Ian

[Clarkson]

Ian, Glad your pleased! Can't wait to start mine up. Does it have a rough idle and what is the idle speed???

David:thumb:

[ian]

David, the idle is quite rough. I also put some 64cc heads on at the same time as the new cam. I was surprised how much I had to advance the static ignition timing to get it to run smooth(ish!) at tickover. Static timing is now 16 degrees BTDC, with vacuum advance disconnected. I reduced the vacuum advance considerably on my adjustable vac. can because it was too strong. After some experimentation I have settled on an idle speed of about 1100rpm, which sounds quite high but you soon get used to it. Much lower than 1000rpm the idle is so rough the car shakes around too much and the engine feels uncomfortable. With a bit of time and experimentation I hope to have an idle speed of 900-1000rpm. It sounds f****** excellent, really intimidating when you're at the lights next to chavscum w***s in their tarty Novas ready for a burn off I have always run this car on the old V12 Dax sidepipes which have little or no silencing so they have always been loud, but now it is much louder, I think they may land me in trouble.... Hope the build goes OK, don't forget the oil pump primer (a proper one, not an old screwdriver in a drill.) Cheers. Ian.