compression readings. should i be worried?

Hello Everyone!

As I've been working on my Maxim almost everyday since i purchased it, I've been coming across more and more of the previous owner's neglect.

It leaks out of the tachometer cable, and all that was done to rectify the problem was a little gorilla glue... :evil: , all 4 of the intake manifold boots dry rotted all the way through, and 7 out of the 8 valves are out of spec. this worries me because before i ripped the valve cover off to check clearance, i did a compression test and 3 out of the 4 cylinders were about 130-132, and the number 1 cylinder was at about 112. The bike runs, but on the number one cylinder pops out the front of the carb. also my number 4 exhaust is not bolted up like the rest it is studded on with nuts holding it down.. :?

i sent PM to chacal for the parts, and am doing my best to clean up the neglect and turn this awsome bike into the head turning vision i have in my head. should i be worried about the motor? will adjusting the valve clearance really help bring the pep back into the motor?


ps. all of the exhaust valves are out of spec, and the number one cylinder(the one that backfires) is the only intake valve that is in spec. band aid job?

thanks,
andy 8)

 

Get the valves shimmed right then do another compression test. If a valve was so far out of spec that it stayed open then you would have less compression in that cylinder.

130's isn't bad, as long as all four are close to each other. But you need the valves in spec to get a proper reading.

And you're going to want to get the boots replaced or it will run way lean. Just be careful when you go at the studs, they break easy. Use lots of Kroil, and even more patience.

 

Sure will tskaz! thank you very much!

one more question! i remember that they weren't too far out of spec i think they were only at .004 in on my exhaust, i'm just very puzzled at why that one cylinder was backfiring, even though the intake valve was in spec. could it be because of the lean condition from the boots?

 

It is possible you have a lean misfire, but first things first.
Get those valves adjusted and, while you are waiting on the shims, salvage or replace your intake boot. Odds are also good your carb shaft seals are toast given the vintage of your model. Not hard to replace but requires a day or two of your time to get it all done right.

 

The exhaust system is supposed to be held on by nuts on studs; if you have bolts it's somebody's replacement job.

If your tach cable was leaking, the problem is the oil seal inside the tach gear housing has died and it's pumping oil up into the cable. Not good. The real fix is here: http://xjbikes.com/Forums/viewtopic/t=19538.html

Get the valves in spec first; then do a compression test. Meanwhile, pull the carbs and get busy; you don't need the carbs on the bike to run a compression test.

 

THANK YOU VERY MUCH FITZ AND ROBERT!

WAITING ON PARTS AS WE SPEAK, I'LL POST AS SOON AS I'M FINISHED!

 

hey guys, possible stupid question.

after reviewing my measured clearances today, most of the clearances are too tight, and i don't understand why. I'm pretty sure i did it correctly. i not only own the haynes manual, but i read the thread with pics on how to do it. i don't think the PO did ANY sort of real maintenance to this thing :evil: and I'm just curious while I'm waiting for my parts from chacal.

thank you for your time!

Andy

 

Finding all the valves needing to be adjusted is all too common on a bike that used starved for maintenance.

Do a WET Test.
See what happens to Number -1.

If the Compression does NOT rise, in Number-1, following the Wet Test with Valves Shimmed in-specs ... the problem's the Valve.

 

Valve clearances get TIGHTER as the valve pounds into the seat. They do not wear at the cam/shim interface. The valve then moves closer to the cam as it wears, reducing clearance.

Remember too, that the reading is done on a cold engine, and all those parts expand when it gets up to temperature. If the valves clearance is never adjusted and there is no gap, they can be held open, resulting in burned valves that requires pulling the head.

 

ahhh, i understand now, i thought that the valve shim wore down, not that they pounded into the seat! Now i know, and knowing is half the battle.

and as soon as i get my parts in the mail that's the frst thing i'm doing, thanks much rick!


thank you everyone, i'll post results as soon as i can!

 

You realize that until you remove and read the shims, you don't know which size to get, right?

Or are you way ahead of me and did all that already?

You did find the valve adjustment how-to, I'm hoping?

 

yes fitz i read the how to thread with all the pictures......freaking AMAZING help!!!!

i just got my parts in the mail from chaccal( super fast delivery with painless ordering process, speechless when i already received them in the mail today! ) i needed the tool to hold down the bucket. i have the page in the haynes manual with the conversions of the measured clearance and what i pull out to what i need to get bookmarked. Also, i'm bringing my micrometer home to ACTUALLY measure the thickness of the shim, and not go off of the reading. And first thing tomorrow when i get out of work guess what i'm going to be doing on my friday night....bikes, beer, and bbq. 8)

 

ALSO!!!!

I'm replacing all of my intake manifolds tomorrow. In regards to the gasket that sits between the block and boot, after cleaning the mating surface, would it be appropriate to put a little RTV/ black silicone down on the block side to help it seal/seat better?

 

Replacing Manifolds is easier said than done.
There is a high probability that several (maybe all) the Cap Screw Fasteners may be SEIZED.

The Soft Steel Cap Screws holding the Manifolds in place chemically bond with the Head.
The Soft Steel TWISTS instead of loosening and backing-out.
The Fastener SNAPS-OFF leaving you with a Major Project to extract fragments.

Know the Situation you face before embarking on what seems should be quite a simple and straight-forward exercise in removing fasteners and installing new Parts.

A Manifold Job can "Go South" in an eye-blink.

Exercise Extreme Caution.
That Manifold Bolt you think is turning, ... may be "Twisting".

 

Hey guys, sorry i havent posted in a while. School and work has been kicking me in the groin.

Just finished a three hour endevour with frustrating results...

i adjusted all of my valve clearances and checked my compression....now my compression in cylinders 1 and 2 is about 110 and my compression in cylinders 3 and 4 is about 150. i'm pretty sure that all my clearances are in spec, and i double checked before reinstalling the cover. the bike will start and run...but runs like poop.

when removing the cover, i did bump the chain guide/bridge out of it's place, but i put it back into place. Also, while i was turning the motor by hand, the timing marks on the cams did look a bit off when i aligned the "t" mark down below.

i was thinking about pulling the cover off tomorrow and checking my clearances again, and possibly looking in to realigning the cams and tensoning the chain.

however, as i am still a beginner, new to this motorbike, and all you guys have lots of years on me, i figured i'd come ask...no BEG for some advice seeing as i am very down on this one and i need some help.

thanks yet again, and i am dying to fix this mess. you guys are always so helpful, you rock!

 

The valve timing once set can't be adjusted, if it's one tooth out that's big trouble.
So check the compression again putting a tablespoon of motor oil in each cylinder, disconect the TCI or ground the plugs, hold the throttle wide open & remove the air filter, give us the new readings & we will give you the next step...

 

Cylinders 1 and 2 = 110

Cylinders 3 and 4 = 150

 

1 & 2 have problems with valve seats & or guides.

 

If you didn't remove your cam sprockets I doubt you skipped a tooth on the timing chain, though it could have been misaligned by a po.

My bike has the front cam marker 1mm forward and the rear 1mm aft and it is correct.

Did you recheck your clearances after you swapped your shims?

Also, have you cleaned and bench synced your carbs? It's not going to affect compression but your bike should not be unridable based on your readings.

As far as your "running like poop", your compression is not the main issue. Based on your numbers, your description of how your bike runs should be "it idles and rides good, but I can tell there is some lack in performance", not it runs like "poop"

 

This IS your answer. Your "dry" and "wet" tests produced virtually the same results. So you're lucky-- it's not rings.

How many miles on the bike? I'd say if it's under about 30K, you've most likely burnt (or begun to burn) a couple of valves. Over 30K and I'd buy worn valve guides.

Either way, if you want to fix it the next step is to pull the head and investigate.