replacing headgaskets on my '82 cm450, what can i do while its apart?

[binks]

about to tear down my '82 cm450 to fix some oil leaks and routine maintenance on the motor.
while shes apart, is there anything i can do to upgrade the power some? bigger pistons and new cylinders? i know carbs would be everyones first recommendation, but my carbs are new and ill just rejet them.

but is it possible to install larger pistons and the proper size cylinders to run them to change compression some. what pistons would i wanna run if so? what clyinders? are there companies out there who make such things?

im new to these kinds of motors, im a small engine tech for a powersports shop so i understand rebuilding smaller engines, pretty much the same thing though.

thanks in advance for any help.

heres a picture of her from the other day.

 

[binks]

46 views and no input. really dont wanna start doing things on my own and blow my motor up.
but hmm...its only a 450. maybe i should toss a 550 in her or bigger.

 

[SONICJK]

There are just too many variables to give you a really good answer.
The quick one is no, they don't make ready made kits like they do for smaller newer stuff. You can't just go buy pistons and jugs and swap them out. You have to get pistons and then have your cylinders bored to fit the pistons.

I am not a 450 guru so I don't know what's out there, but I'd wager there are not many ready made options for that bike, its not modified that way very often.

That being said I am sure there are pistons out there that will work a treat, you'll just have to do some research to find them.

 

[binks]

thanks for the input. i figured they didnt make anything.
im also realizing parts for this motor are nearly impossible to find. i pulled the motor today and discovered a few things i didnt like and all answered my questions as to why the head gasket popped. but i need to replace an exhaust valve. while doing so i wanna replace them all, along with new everything else just because.
butttt...all valves for this are obsolete. very upsetting.

anyone know the exact dimensions and size of the oem valves on this motor? ill measure if needed once shes fully apart, id just love to get on top of ordering all the parts i need.

can anyone confirm the cylinder bore as well. 75mm correct?

 

[binks]

just did a bit of research and reading on this site. are the motors from the cb450 the same as the cm450c? it seems so, and i believe i can find parts for that motor easier then i can find them for mine.
any input on that?

 

[mydlyfkryzis]

Go on a Honda Dealer site (I use www.houseofhonda.com) and look at the microfiche parts listings...Get the part numbers for your bike, then search the internet for the part numbers....

Or check the model you think is similar. If the part number is the same, it will fit....

 

[Drey6]

CB/CM were the same from 82' to 86' I believe. It's the nighthawk and can be searched as a CB450SC and the CM450SC. Check out http://www.davidsilverspares.com for anything you can no longer find new for your bike. Take the part number from a fiche like mydlyfkryzis recommended, and search the part number in the david spares site search function and I will tell you if they have it. Should have luck there.

I'd hone the cylinders and overbore only if needed, buy new standard piston ring sets for each cylinder. I'm doing a rebuild on my 81' CM400 engine that is identical to yours other than the 50cc difference, the 6th gear on the transmission and the oil cooler. I have a thread going on a whole engine rebuild and the last of my parts should be arriving shortly to button it up. Also, inspect the valves to spec, clean and lap them. Most likely are fine and could end up being a waste of money to get new.

Lastly, tap ALL threads (especially head threads) to remove shit that could result in an improper torque when you button her up.

 

[binks]

thanks guys for the good advice. as far as finding parts online, 99% of places do not carry them for the cm450c so ill search for the cb450 parts.

i tore my motor apart today, ill be posting alot of pictures soon. but i found all my problems. broken and bent exhaust valve on the right hand side. i still have tracked down a missing valve tappet screw, im sure ill find it when i break open the bottom end.

as far as valves go, if i take the proper measurements, could i find a set of valves from another motor, i.e the cb450, but aftermarket? since im upping my compression, id like stronger valves, along with valve springs. the springs feel very familiar to me, theyre almost identical to intake valves for a b series honda/acura engine. if they match, could it be possible for me to run skunk 2 valves in my motor(i used skunk 2 as an example because i have a set laying around) for one of my civic builds??

 

[binks]

i seemed to have forgotten about this thread.
i have alot of updates ill get around too, but i need serious help right now.

head slightly milled. new exhaust valve/guide installed by machine shop. cylinders honed. pistons acid bathed. 100% new gasket kit.
assembled. torqued headstuds to 27lbs instead of 25 due to age and wear along with the milling to the head. adjusted valves. fires right up. blows tons of white smoke. recheck valves. recheck headstud torque. fires up. blows smoke. (must be all my assembly lube burning off the cylinders). check valves again. all set to .006 on exhaust and .004 on intake.

take her out on her first test ride. pulls strong, still blowing smoke in neutral, not so much in gear. idle is rough. real high, cant seem to get it lower(i dropped my carbs off the top of my bike, may have something to do with it. ill check into it tomorrow). only rode her about a half mile around my neighborhood.
last road home, backfires from both chambers when slowing down, starts bogging. pull into the backyard(my dumbass didnt pay attention to my bench next to the fire pit and caught my shifter arm on the leg, bent it out about 90 degrees. fml), but as i get to the garage, i see oil on my pant leg. oil is pissing from the top end. seems as i didnt put my valve cover gasket on correctly. also seems like oil is seeping from the top side of the headgasket.
things i need to know:
proper timing method and chain tensioning method for my motor.
should i drop my torque on the headstuds?
what could be causing so much smoke? valve lash adjustment??

im taking the motor completely back apart tomorrow night after work and rebuilding from the bottom up. checking my piston rings as well.

all help is appreciated, as always. and sorry if this is all scrambled, ive had a very long day.

 

[Chancho196]

You honed the bores, but didn't replace piston rings? That'll be the smoking issue. Valve clearances won't affect oil burning - the oil is getting past the pistons, or down through the valve guides. To be honest, if you want more from an old engine it's sometimes better to think about something bigger in the first place. Cheaper in the long run, and less heartache.