1987 CR 250 jetting problems/ head gasket leak discovered

ZOOK250
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ZOOK250
Edited Date/Time 8/12/2016 3:47pm
hey guys,

a few weeks ago i finally got my 87 out. she ran amazing for about 4 laps then something strange happened.

in a corner she went wide open and the kill switch wouldn't work, so i pulled the plug cap and it didn't shut down. i had to shut off the fuel and lay it over.

it was running really hot, i put engine ice in her and probably half of it boiled out.

the main jet is a 162, im running a pro-circuit works pipe, our elevation is 785ft, and average riding temperature is between 77 and 86 Fahrenheit.

i did a leak down test and the only leaks i could find were at both of the top power valve covers. the throttle tube was a bit on the sticky side , but the slide appeared to be working fine. the idle knob had to be turned way up to get her to idle a bit, almost like the choke is half way up.

any ideas? the other PJ carb i have has a 180 main jet in it.







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450exc115
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450exc115 8/10/2016 8:43am
8/10/2016 8:43am
Check for crap in the pilot. I cooked my 81 CR with a plugged pilot jet. I always replace jets and fuel needle when I bring a bike back to life
Brett Campbell 8/10/2016 9:49am
8/10/2016 9:49am
Runaway engine. Next time just put it in gear, hold the brakes and choke it down. They say you can hold the throttle wide open and it will shut off. Never tried it myself. I would say you are running lean for some reason. Check for air leaks.
StevieD113 8/10/2016 10:16am
8/10/2016 10:16am
Sounds like you have an air leak. Check the base gasket, crank seals, the intake manifold and gaskets.

Had it happen with 1979 Rocket motor, it was sucking the base gasket in on one side. (The top face of the LH crank case was bent slightly from a previous owner/builder being a ham fisted idiot!!) It would run perfectly for a lap or so, then as it got hot everything expanded a little, and it would suck the base gasket in and it would stick wide open.

When they suck air they can run REALLY hot, really fast as all the extra air leans them out. The extra heat could cause it to pre-ignite, that might be why pulling the plug cap didnt' do anything.

Stevie
ZOOK250
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ZOOK250 8/10/2016 12:25pm
8/10/2016 12:25pm
thanks for the suggestions, i would have done the clutch dump , but just as i was downshifting into the corner, the splines on the stock shifter slipped and i went into neutral. because the shifter was now shitting on the bottom of the frame it was stuck in neutral and revving to the moon. i couldnt get it to go into gear at that point. you will see on the bottom picture that the shifter is not on the bike. it was just a series of bad luck incidents.

The Shop

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ZOOK250
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ZOOK250 8/10/2016 12:31pm
8/10/2016 12:31pm
could an air leak in the power valve cover cause this?
benchracermx 8/10/2016 2:03pm
8/10/2016 2:03pm
Brett Campbell wrote:
Runaway engine. Next time just put it in gear, hold the brakes and choke it down. They say you can hold the throttle wide open and...
Runaway engine. Next time just put it in gear, hold the brakes and choke it down. They say you can hold the throttle wide open and it will shut off. Never tried it myself. I would say you are running lean for some reason. Check for air leaks.
Lol... My 89 did exactly this... My kill switch was faulty too and mine was wide open down a rythem section... I tried to stall it and dump the clutch.. Nothing worked, bike nipped up... New piston and barrel replate required
Brett Campbell 8/10/2016 5:48pm
8/10/2016 5:48pm Edited Date/Time 8/10/2016 5:49pm
ZOOK250 wrote:
could an air leak in the power valve cover cause this?
I don't see it being the cause, but try spraying the covers with ether (starting fluid) with the engine running and see if it reacts. Remember, if it runs away again to hold the brakes (2nd gear) when you dump the clutch.
Brett Campbell 8/10/2016 6:00pm
8/10/2016 6:00pm Edited Date/Time 8/10/2016 6:01pm
Engine Runaway

Engine runaway is when the motor revs up freely on it's own. Preignition is taking place in which no spark is needed. A red spark plug or piece of glowing carbon pre-ignites the fuel mixture and causes engine to continue picking up speed until failure. That's why the kill switch and removing the plug cap does not shut it off.

Causes

In order for this to happen, there has to be a lean condition present. Any kind of air leak could potentially lead to destruction. Intake gaskets, carb gaskets and crank seals seem to be common culprits.

I had this happen once when I turned the fuel off to run the fuel out of the bowl, which was the cause of the lean condition.
ZOOK250
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ZOOK250 8/10/2016 8:03pm
8/10/2016 8:03pm
Do you think 162 on the main might be a little lean? I was going to pick up a 168 , 170, 172 and see which one she likes. Also what are you opinions on engine ice? Ive never had a bike get that hot after 4 laps. I am going to use regular coolant this weekend.
CamP
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CamP 8/10/2016 8:35pm
8/10/2016 8:35pm
More than likely, your radiators are plugged up with magnesium oxide from the waterpump housing.
RyanLester761
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RyanLester761 8/10/2016 9:07pm
8/10/2016 9:07pm
I have a 1987 cr250 as well. My bike did the same thing...

Check your throttle cable where it enters the carb cap. A good tip is to safety wire the cable down. It can pull up and sit on top of the brass fitting.
Brett Campbell 8/11/2016 4:37am
8/11/2016 4:37am
ZOOK250 wrote:
Do you think 162 on the main might be a little lean? I was going to pick up a 168 , 170, 172 and see which...
Do you think 162 on the main might be a little lean? I was going to pick up a 168 , 170, 172 and see which one she likes. Also what are you opinions on engine ice? Ive never had a bike get that hot after 4 laps. I am going to use regular coolant this weekend.
It wouldn't be a bad idea to fatten it up a bit. My 88 CR250 came from the factory with a 175, which is a little fat. Like camp said, check your cooling system and make sure it is working properly. I would put a temperature gauge on it to make sure I didn't burn it up. Cheap insurance!
ZOOK250
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ZOOK250 8/11/2016 5:32am
8/11/2016 5:32am Edited Date/Time 8/11/2016 6:23am
thanks guys. i have brand new aluminum radiators, but maybe the silicone hoses are more restrictive than the original. i noticed that the "Y" hose has more of a bend than the original. is there an easy way to tell if your water pump is working properly?
450exc115
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450exc115 8/11/2016 11:56am
8/11/2016 11:56am
I'm betting on an air leak or fuel starvation. I've seen it before on both my YZ and CR. A leak down test will confirm if you have an air leak and a good inspection of the carb can tell you if you have a fuel problem.
ZOOK250
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ZOOK250 8/12/2016 10:15am
8/12/2016 10:15am
ive been having trouble getting a good seal on my intake boot. i have a compression tester that has been modified to allow me to pump air in through the spark plug hole. i have the exhaust sealed. if i put a plug with a pressure gauge in the intake boot, will this give me an accurate pressure reading with the reed valve? should i take out the reed's?
ZOOK250
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ZOOK250 8/12/2016 3:45pm
8/12/2016 3:45pm
Ok. The head gasket was leaking , not bad, but i guess any leak is bad. The gasket is very thin. So i started looking through my box of parts and i found w old gaskets. One is 2 to 3 times thicker material with a metal ring . the other one is made up of 3 gaskets held together with copper fastening rings. This one is probable 5 to 6 times thicker if not more. The mechanic that built the engine had to use washers on the acorn nuts to be able to get the head properly torqued. Now what?

ZOOK250
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ZOOK250 8/12/2016 4:18pm
8/12/2016 4:18pm
Ok somthing new. Looks like one of the cylinder head bolts was snapped at sometime and it was somehow epoxied back in place. I need the bike this weekend can i jb weld this back in for temporary use?
RyanLester761
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RyanLester761 8/12/2016 4:27pm
8/12/2016 4:27pm
Can you use an easy-out to get the stud out? Your local hardware store or auto parts store should have that... and a new stud, if you don't have it. I wouldn't use jb weld.

Pit Row

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ZOOK250
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ZOOK250 8/12/2016 4:41pm
8/12/2016 4:41pm
I have an extra cylinder but i cant get a stud out of it. Is there a technique to getting them out? I have and easy out as well.
ZOOK250
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ZOOK250 8/12/2016 4:44pm
8/12/2016 4:44pm
Got it out. Now for the easy out. May the force be with me.
450exc115
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450exc115 8/12/2016 4:48pm
8/12/2016 4:48pm
Heat and a reverse cut drill bit is your friend. Can you post a picture.
Kidkawie
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Kidkawie 8/12/2016 4:50pm
8/12/2016 4:50pm
Have you pulled the right side cover for corrosion? You cant jet a broken engine, do a pressure test.
ZOOK250
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ZOOK250 8/12/2016 10:58pm
8/12/2016 10:58pm Edited Date/Time 8/12/2016 10:59pm
Right side cover is in perfecr shape. Not a bit of oxidation. Turns out that the prvious owner tried to do a helicoil but drilled the hole on an angle. The stud is off center. After i cleaned out the epoxy , i could see threads. I dropped in an M8 coil without having to drill it out. When i threaded in the stud it was off center. Thats why it was epoxied in. Now i need to take it to a shop that has an idea how to fix this mess.
ZOOK250
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ZOOK250 8/12/2016 11:03pm
8/12/2016 11:03pm Edited Date/Time 8/12/2016 11:05pm
With the head leaking right next to the water jacket inlet on the head, i think i was over pressurizing the cooling system. I blew half of it out of the rad. When i went to empty the coolant there wasnt much left.
StevieD113 8/13/2016 12:56am
8/13/2016 12:56am Edited Date/Time 8/13/2016 12:57am
The old leaky head gasket trick.. gets 'em every time!!

Your issue with the varying thickness of head gaskets is something to be careful of. Most generic gasket sets come listed 86-91 or 89-91 or some variation on the years. These usually come with a very thin (0.25mm) metal head gasket which is not correct for the early 87/87's.

If you look at the cylinder head of the 86/87's, the combustion chamber isn't very deep, in fact it looks like the head has been skimmed! The later models, the chamber is machined deeper with very distinct "lip" around the edge.

The '86-'87's used a thicker head gasket. (it's either 1mm or .75mm. I can't find my old one to measure up!) which is still available from Honda, part #12254-KS7-881. The original was fiber with a metal inner ring, the newer version is a multi layer metal type.

It sounds like your motor has had the later thin head gasket fitted, which not only causes sealing issues (I imagine an epoxied in stud wouldn't help with that either!!) it also can cause detonation as it basically drops 0.5-0.75mm off the cylinder head!!

Stevie


berniepiet
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berniepiet 8/13/2016 7:27am
8/13/2016 7:27am
ZOOK250 wrote:
Do you think 162 on the main might be a little lean? I was going to pick up a 168 , 170, 172 and see which...
Do you think 162 on the main might be a little lean? I was going to pick up a 168 , 170, 172 and see which one she likes. Also what are you opinions on engine ice? Ive never had a bike get that hot after 4 laps. I am going to use regular coolant this weekend.
162 may be a scosh lean for your altitude but not much. Plug will tell you once you get the othe issues worked out. Look up a product called Evans NPG. It is a petroleum based coolant ( no water in it) has higher boiling point & prevents the corrosion problem
wolfy0067
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wolfy0067 8/15/2016 4:04am
8/15/2016 4:04am
Zook, have the cylinder oring'd I was also having head gasket leaks on my CR265, a local machine shop that races Micro Sprints preforms this service and recuts the head combustion chamber, think it cost about 150 buck to complete. they sell the oring kits for this mod. 162 m is to lean, start with the 180 and jet back after engine is run in. I think I ended up with a178m. You will want to perform a squish clearance check, before disassembly, so all parts are machine properly. One last thing, I do not recommend boring a cylinder over .040 on the CR, to make it work properly it has to have to much piston to cylinder clearance, the issue is the exhaust pushes the piston against the intake and you end up with a complete piston seizure, been there done that one, never again.

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