Author Topic: Help!!!! valve lash increasing when warming up (Read 3107 times)

750caferacer · « **on:** April 08, 2020, 04:41:35 AM »

I have a 1978 cb750k 30k on bottom end fresh rebuilt top end. I was riding not to long ago after just changing oil and filter and tuning the carbs a little because they were to rich. i believe i tweaked it to much and leaned it out i was riding with my girl on the back and the bike had no signs of any thing wacky going on great power with great oil pressure 75psi + and then it squealed really loud i grab the clutch and it shut off, was still coasting and let out the clutch and it locked down the back tire and the motor did nothing. i pulled off the road thinking the motor was locked down in the bottom end i let the bike cool off for about 10 min and it started right up like nothing ever happened no ticks no knocks nothing, seems like it over heated..... took off down the road and made it about a mile and it lost power miss firing and died, pulled off again and let it cool off while we waited for a rescue to come pick us up. i figured the bike was screwed so i started it up just for the hell of it and it was missing like crazy shut it off and got it home. Drained the oil, cause it smelt burnt but not black still golden color. changed the oil 20w50 of course. i tuned the carb rich and i readjusted the valve because i checked them figuring since it got "hot" my clearances might be off, found almost all the adjuster nuts and screws were still tight but the lash was like .005 int and .006 exhaust, when i adjust my valves i always do it cold and .002 int and .003 exhaust on the compression stroke of each cylinder. i readjusted them like i always do and started the bike up and it ran great!

so here is the kicker ever since then i can start the bike cold and it runs amazing all kinds of power and smooth idle......unit it get all the way to operating temp and then the valve lash starts getting looser and looser and the bike starts ticking like crazy of course. check the lash while its warm and it always around .005 int and .006 exhaust the bike will cool off over night and the lash is still .005 & .006. ill readjust the valves and it does it all over again. my only thought would be weak valve spring i didnt change them during the top end rebuild because the machine shop said they were good at that time im wondering if i overheated the motor fatiguing the valve spring maybe... im lost can anyone help before i ether tear this motor apart again or just drain all the fluids and make it in to man cave art!

bryanj · « **Reply #1 on:** April 08, 2020, 06:05:53 AM »

Hate to say it but it sounds like lack of oil to the cam, did you clean out the restrictor jets? Did you use any jointing compound?

750caferacer · « **Reply #2 on:** April 08, 2020, 06:30:25 AM »

see that the weird thing since the top end rebuild i have put like 2k on the bike no problem some of the rides were 100 to 150 miles long now i cant make it 5 miles :/ ...
and yes the oil flow jets and the passages to every thing was clean and i checked it all for flow.
unless somethings stopping it up now....

bryanj · « **Reply #3 on:** April 08, 2020, 07:13:47 AM »

One tiny pice of gasket scraped into an oilway or a tiny piece of gasket goo broken loose will destroy a top end. Try starting it with the inspection caps off and if everything is not flooded in oil (i.e. spraying out the holes) you have a problem.

750caferacer · « **Reply #4 on:** April 08, 2020, 07:27:14 AM »

i will do that!
so if thats the case then i might get lucky if no damage has been done to re clean everything top end wise and my oil flow ports and cross my fingers?

MRieck · « **Reply #5 on:** April 08, 2020, 08:15:46 AM »

The oil jet(s) is/are restricted. The valve lash keeps increasing because the metal is coming off the rocker arm pads and cam lobes.

754 · « **Reply #6 on:** April 08, 2020, 09:22:49 AM »

If it stuck at any time, there has been damaged parts.

750caferacer · « **Reply #7 on:** April 08, 2020, 09:58:25 AM »

ugh i just spend so much money on this bike last year build it and the rebuilding the top end.
is there a way to be proactive and prevent this like pre filtering the oil while filling it or anything?

heres a few pics from the top end rebuild

bryanj · « **Reply #8 on:** April 08, 2020, 10:03:33 AM »

Its nothing to do with pouring oil in, its oilway cleanliness on rebuild i'm afraid

PeWe · « **Reply #9 on:** April 08, 2020, 10:26:31 AM »

The oil is cleaned in the oil filter just before the way to crank and up to the head.
Important that the correct washer and spring is mounted inside filter cover pressing filter to the engine case so the dirty particles from oil pump is stopped and cannot pass by. Before that direct from oil tank.

So if a terrorist open oil tank and put sand inside, the "only" damage should be oil pump only if filter is correctly mounted.

Possible to make mistake with additional sealer on base and head gaskets near the 2 oil feed holes sealed by o-rings, each side of the cam chain tunnel on inlet side.
Or way too much sealer between cases near the 18x3mm o-ring at front so it enter the oil feed after filter.

Or dirt in the head, holes going up via the oil restrictors not cleaned before assembly.
Or dirt inside cam holders. These have small holes that need to be degreased and blown free with compressed air.

I'm convinced that eager to make it oil leak free using plenty of not needed sealer has ruined many engines.

I have had thoughts about this many times, never had that bad luck.

750caferacer · « **Reply #10 on:** April 08, 2020, 10:40:24 AM »

i did put sealant on the cylinder base gasket on other sides of the gasket trying to prevent leaking and guess what it still somewhat seeps and my valve train is SOL now :/
who knew being to thorough was a bad thing.

750caferacer · « **Reply #11 on:** April 08, 2020, 10:49:38 AM »

well anyone got any good used cam and rockers and rocker boxes just in case? or a place to get good new stuff?

754 · « **Reply #12 on:** April 08, 2020, 10:57:11 AM »

This .. THIS.. is exactly what I meant when I asked if you used silicone on the topend.
Any sealer if applied heavy can be a problem..

The key word here, and always has been is sparingly... apply sparingly..

The good part about mistakes is we can learn from them...

So I will say it one more time.. remove your outer valve caps , and tell us how oily it looks in there.. then get a strong light and look.

If you have to pull the top end, and want to avoid pulling engine, Scotty has a frame kit, to allow top end to be able to be pulled with engine in frame. Takes around an hour to install.

750caferacer · « **Reply #13 on:** April 08, 2020, 11:09:14 AM »

754 im sorry i forgot all bout the base gasket... im gonna look tonight and let yall know later.

thanks so much for the help and advise everyone will keep yall posted!

750caferacer · « **Reply #14 on:** April 08, 2020, 06:16:12 PM »

this is 1 & 4 intake and exhaust. couldnt see nothing so i started it up with the bike no leaning on stand

750caferacer · « **Reply #15 on:** April 08, 2020, 06:17:05 PM »

this is cylinder 4 intake and exhaust

bryanj · « **Reply #16 on:** April 09, 2020, 12:16:21 AM »

If you didnt get covered in oil its engine out time

Old Scrambler · « **Reply #17 on:** April 09, 2020, 08:32:56 AM »

Based on OP motor tear-down #2 is first to exhibit hot cam bearing races.......one guy made it home on #3-4 after the cam broke between the bearing and the sprocket

754 · « **Reply #18 on:** April 09, 2020, 10:11:35 AM »

Well it sure looks like its getting some oil..

750caferacer · « **Reply #19 on:** April 10, 2020, 06:32:23 AM »

it only gettin oil to 3 & 4 i believe no oil built up on 1 & 2 side. 4 exhaust side built up oil and threw it every where with the cover off.

bryanj · « **Reply #20 on:** April 10, 2020, 07:16:51 AM »

Like i said engine out and deep pocket time

PeWe · « **Reply #21 on:** April 10, 2020, 07:43:27 AM »

Used cam holders with rockers available on eBay. Stock cam too. I found a very good low mile K7 cam for $50 USD a year ago.

All for 150 I guess ..

If living in USA no horrible shipping and customs costs.

754 · « **Reply #22 on:** April 10, 2020, 08:46:11 AM »

Is the 1 and 2 side going loose on valves more than the other side?

jakec · « **Reply #23 on:** April 10, 2020, 09:55:54 AM »

Quote from: bryanj on April 10, 2020, 07:16:51 AM

Like i said engine out and deep pocket time

Is this why you see so many restored bikes that are "never fired?"

bryanj · « **Reply #24 on:** April 10, 2020, 10:47:02 AM »

Only if people dont trust their own work!!!

News:

Author Topic: Help!!!! valve lash increasing when warming up (Read 3107 times)