Petrol head thread!!!

[billy rubin]

shitfire.

im trying to get the cylinder head down on my race bike and today i got ready to clay the pistons. i have to modify the piston crowns zo they dont zmack into the head because the compression is so high. i do that by putting little blobs of clay on the pistons and rotating the motor over top dead center. then i .meazure how thick the squashed parts are.

anyway, i put it together and started to adjust the valvez, and the adjuster screws just kept giing down and down. i took it apart to make sure the new pushrods were seated and tried again. same thing. couldnt figure it out.

finally i took the pushrods out and measured them. tbey were a half inch too short.

triumph used 6-inch pushrods from 1963 to 1973, and then 5.5-inch pushrods from then on. my lushrods were labelled correctly for my older machine, but someone put a set of new ones in the box.

so now i have to order replacements and wait, and that puts me a week behind getting this thing out to break in the rings before the snow fliez.

rats.

[Icarus]

BR:  when you get the new pushrods, You should check the valve timing carefully, with degree wheel and cam card.  Just a wee bit of difference in pushrod length will alter the valve timing and duration on account of the relative positions of the rockers. You either have high domed pistons or have milled some off the length off the cylinder casting. Domed pistons do not affect the valve  timing but milling the cylinder casting does.... big time.  Clay the valve pockets, for sure, when you get the new parts.  But I suspect that you know that stuff. 

[billy rubin]

you're absolutely right. it takes me a whole day to set the valve timing, because i'm fussy. triumphs have fifty teeth in the camwheels, so each tooth is good for 14.4 degrees, and then there are three keyways, one-third of a tooth apart. so i can come within 2.4 degrees of what i'm looking for, but no better than that. i run five to six degrees retarded from the factory settings. that's supposed to make it weak on the top end, but it doesn't work that way for me.

the cams i use are ultra precise on the lobes-- literally, there is zero measurable runout when i spin them-- a 0.001-inch dial indicator is totally motionless when i rotate back and forth on the base circle-- but the key slots aren't so well-located. the ones i have now are the same grind as before, but are about two degrees advanced from the ones that gave me my best speeds, and i can't get any closer to what i want than that.



my pistons are pretty domed-- 11.75 to 1. i have to run two spark plugs per cylinder to keep the motor from detonating, even with 109 octane gasoline.

[Dark Lightning]

Holy shit, that's a REAL dome! I've run 13:1 in a Small Block Chevy (SBC), but the combustion chamber is a bit smaller than what you have there. No surprise about needing two spark plugs! I realize how small the keys are, but is it possible to get an offset key that can give you what you need? Maybe the amount you need would weaken the key too much? I've degreed cams in SBCs, but that just takes a pill with an offset center hole.

[billy rubin]

its a true hemi head, with all the attendant issuez. with a stock ignition it takes 38 degree of spark advance to run. with two plugs i can use 30, and some people run 20 btdc. hemi heads were great in the 1930s, and their time iz way over. but its what i have.

i previously had the cams set at 106/109 degrees using the lobe centerlines, and now the closest i can get is 104/107. the keys are really, really tiny-- only 1/8 inch wide, so i could file something, but it would be hit or miss. i keep buying old camwheels at swapmeets looking for onez that are out of spec, but zo far theyve all been spot on.

13 to 1 is pretty fierce.  were you running alcohol in those things?

[hermes2015]

From the entirely different perspective of a sculptor manqué, I am drooling over those beautiful objects. With the addition of some wings, they would make excellent Hermes helmets.

[billy rubin]

lol

thats before they get polished



theyre beautiful things, and horrifyingly expensive. i have to buy four at a time or they wont make them. i complained about it to the man who sets them up, and he said. you LSR guys use up pistons pretty quick. dont worry about it.

and he was right. i suppose i have two hundred miles or so on thiz machine, and im on the third set of pistons.

[Dark Lightning]

its a true hemi head, with all the attendant issuez. with a stock ignition it takes 38 degree of spark advance to run. with two plugs i can use 30, and some people run 20 btdc. hemi heads were great in the 1930s, and their time iz way over. but its what i have.

i previously had the cams set at 106/109 degrees using the lobe centerlines, and now the closest i can get is 104/107. the keys are really, really tiny-- only 1/8 inch wide, so i could file something, but it would be hit or miss. i keep buying old camwheels at swapmeets looking for onez that are out of spec, but zo far theyve all been spot on.

13 to 1 is pretty fierce.  were you running alcohol in those things?

Back then we had to use race fuel with some stupid high octane number, and/or use an octane booster that tetraethyl lead in it. It wasn't anything to try and drive on the street, it was just too expensive.

Are the gears steel or aluminum? I guess either way one could weld the key way full and re-machine the slot in a better place.

[billy rubin]

theyre steel. before i start welding im going to hit up the swap meets some more and see if i can find some mis-machined a bit that i can tweak. the british stuff is famous for being sloppy in manufacture because the post-war toolingwas all worn out, but so far their cam wheels have all been held to tight specs.

these old machines went through a dry period of 20 years after the british bike industry died, but right now theres a flourishing industry in used and remanufactured parts.

this will continue another twenty years until people like me are all dead, and then it will allfade away. there are people around here with adult grandchildren who werent born when my machine was made, so the clock is ticking.

[billy rubin]

lol

just call me Off-Topic.

[Tank]

lol

just call me Off-Topic.

Hehe. Well now you have your own topic and one that I have no doubt will be very popular reading. As you're new you're probably not aware that my son has worked at McLaren F1 for the last 6 years. He started there running the simulator and moved on to be Fernando Alonso's performance engineer. He's been doing this for Lando Norris this year. But he's leaving in March next year and moving to America.

[jumbojak]

its a true hemi head, with all the attendant issuez. with a stock ignition it takes 38 degree of spark advance to run. with two plugs i can use 30, and some people run 20 btdc. hemi heads were great in the 1930s, and their time iz way over. but its what i have.

i previously had the cams set at 106/109 degrees using the lobe centerlines, and now the closest i can get is 104/107. the keys are really, really tiny-- only 1/8 inch wide, so i could file something, but it would be hit or miss. i keep buying old camwheels at swapmeets looking for onez that are out of spec, but zo far theyve all been spot on.

13 to 1 is pretty fierce.  were you running alcohol in those things?

Back then we had to use race fuel with some stupid high octane number, and/or use an octane booster that tetraethyl lead in it. It wasn't anything to try and drive on the street, it was just too expensive.

Are the gears steel or aluminum? I guess either way one could weld the key way full and re-machine the slot in a better place.

I would braze and then recut the keyway. Perfect job for a shaper if you know someone who has one. Steve Summers would probably jump at the job.

[Buddy]

Ooooh a car thread.

So this is going to be my present to myself once my student loans are paid off. It's a little on the pricey side, but it's only a little bit more expensive than aftermarket, I get discounts at the dealership for being in a MINI club, and there's a warranty. I really want to turn my car into a little autocross beast 

[xSilverPhinx]

shitfire.

im trying to get the cylinder head down on my race bike and today i got ready to clay the pistons. i have to modify the piston crowns zo they dont zmack into the head because the compression is so high. i do that by putting little blobs of clay on the pistons and rotating the motor over top dead center. then i .meazure how thick the squashed parts are.

anyway, i put it together and started to adjust the valvez, and the adjuster screws just kept giing down and down. i took it apart to make sure the new pushrods were seated and tried again. same thing. couldnt figure it out.

finally i took the pushrods out and measured them. tbey were a half inch too short.

triumph used 6-inch pushrods from 1963 to 1973, and then 5.5-inch pushrods from then on. my lushrods were labelled correctly for my older machine, but someone put a set of new ones in the box.

so now i have to order replacements and wait, and that puts me a week behind getting this thing out to break in the rings before the snow fliez.

rats.

All I understood was ''shitfire' and 'rats', so I'm assuming it can't be good.

[hermes2015]

I'm pretty sure all the posts in this thread will be way over my head, but I shall read everything you guys say in the hope of learning something new. I am barely able to put fuel into my tank.