Head rebuild problem

[Bo82CB]

That old gasket looks very weird, that thicknes difference is pretty big!
Have an idea, if you can put very thin layer of poweder or some chalk powder (like used on straight line rope) on the top of your pistons and install head. When head removed maybe some will be left on the valve if your problem is piston to valve clearance!? That "new" head gasket is junk anyway due to multiple tightening and loosening...
What you all think!?

 

[dirtdigger]

About the only reason to double the base gasket would be to raise the cylinders. Maybe the cylinders at some point had been machined to far on the top so they need more piston to cylinder head clearance. Double the gasket is not a good way of doing it but I am not seeing much for thicker base and head gaskets. I have several options on sohc motors but I dont mess with the dohc stuff. The way to check is to mock up a cylinder with base and head gasket, piston in without rings, put a little clay or playdo across the piston and put the head gasket and cylinder head on, rotate the engine, pull the head and see where and what is hitting. Then you can determine how much difference you need to make up to make the correct piston to head clearance. You may check with cyclex see what they have for gaskets or they might know where to get some.

 

[Andy novice]

Put a layer of grease on top of the pistons and rebuilt the head turned the engine both ways between the 2 ends of travel where it jams.
Striped the head down for about the 7th time. no grease anywhere other than the tops of the pistons.
I am at a loss as to what to try next. HELP

 

[dirtdigger]

If it spins without the head but doesnt with the head then it has to be piston hitting the head, nothing else it can be. The piston edge is more than likely protruding past the top of the cylinder at top dead center and hitting the head or head gasket. I would doubt any of the dome is hitting anywhere. The double base gasket is first suspicion that the pistons protrude, someone shade tree "fixed it with two thick base gaskets. If you can determine that it stops rotating at top dead center then you know for sure it is piston to head contact. put it back together but dont tighten the head nuts and the head will probably lift ever so slightly when you rotate it.

 

[Bo82CB]

...or if you can make few spacers in the thicknes of old gasket and put under the head when mounting on the block. This will allow you to see what gets close to what contact wise. DO NOT TORQUE HEAD.
If it turns with out problems you have your answer.

 

[bbaart]

Did you solve the problem? Only thing I was wondering after reading the above thread was; as you are rotating the crank to turn the engine, are you holding the timing chain up as the chain will move also? If not, the chain will bind in the bottom of the engine at or close to the crank. The chain goes down through the head, then the block, and then around a sprocket on the crank. The space gets quite small as it goes down so the chain can easily bind or bunch up down there. I usually attach the chain to the hook of a bungie cord and then have the bungie cord attached to something above the engine. That way you can rotate the crank without having to worry about the timing chain as it will rotate as well. Its also possible that it is already bound up close to the crank and only has about a 1/4 turn of play before it gets stuck.

 

[Andy novice]

Thank for taking an interest.
I have proven that it is a gasket problem and that at some point in the past the head must have been schemed. I have now sourced some thicker gasket to make my own and see it it works.

 

[Andy novice]

Hi all,
Back again after a year!!! Engine has been in tubs all year. The rest of the bike under a cover. I am now semi retired so now have the time to get stuck in.
I came to the conclusion that the head had been over skimmed at some point and that the gasket had been doubled up with the bolts not torqued down correctly.
I now have a replacement head as well as a thicker gasket, another full set of gaskets & seals and a new set of rings coming from America as they were much cheaper than in England.
I will update on progress over the next few weeks with photos, Wish me luck as summer is here.

 

[mikemo]

I'm a bit late to the game, but I've just recently had a motor apart, so it's fresh in my mind.
I'm assuming you didn't remove the pistons from the crank.
Did you install the locating dowl pins in the crankcase before you installed the cylinders (not the cylinder head)?
Did you use a ring compressor when installing the cylinders?
Can you install the base gasket and cylinders, then tighten the cylinder base nut to keep it in place? Does the engine rotate without the cylinder head installed like this? You MUST support the exhaust cam chain with your finger to keep the chain from bunching up under the crank. If it isn't kept under tension, it will bunch up and lock the crankshaft. If it does rotate, do the pistons stick up above the deck of the cylinders? If so, how much?
It really sounds like the exhaust cam chain is hanging up the crank when you are having difficulty.
Good luck to you
Mike M.

 

[Andy novice]

Over the last 4 days I have rebuilt the head - new rings and gaskets, torqued ever thing to spec, set the cams and managed to refit the engine in the frame on my own with the aid of a trolly jack, 2 ratchet straps and some 2x4 wood. All in the middle of a British heat wave of temperatures between 34 and 38 degrees out side and well over 40 in the garage.
Trouble is it will not fire!
Turns over fine, I have fuel in the carbs and a spark at each plug.
Any Ideas?

 

[dirtdigger]

either no or low compression, cam timing off, or spark happening at the wrong time.

 

[Andy novice]

Any ideas how to check without specialist equipment - I am a novice.
If I try to turn the cylinders by hand with the spark plugs in will I get to a point where I can turn no further if I have compression or will I be able to complete the cycle?

 

[dirtdigger]

Borrow or rent the compression tester and timing light

 

[Andy novice]

New problem -
I managed to get it started with the aid of a 2 KW fan heater to worm the engine for first start up. it has started every day since. I have adjusted the fuel mix to around 2 turns and the plugs seem fine. I have ridden it for a couple of miles after each adjustment with a warmed up engine. I have adjusted the idle by the large lack knob between the carbs and it idles fine when on the center stand and returns to idle when revved.
The problem is every time I take it out the revves rise to around 3000 and stay thereat idle. I adjust the idle screw when I get home and repeat the next time I ride it.
If I turn it down any more than it is it stalls at idle.
Any ideas
If you are interested the story so far is below -
Bought a lemon which had been badly repaired in the past with an over skim and a badly repaired crack in the head.
Sourced some replacement parts and put the engine back together last week during a highly unusual British heat wave.
Day one - fitted new piston rings, fitted new gaskets and the pistons in the barrels and torqued everything. Up
Day two - did the cams. cam chains etc almost had a disaster when a bolt fell down the cam chain tunnel. Luckily it landed on a ledge and I retrieved it with a magnet. see photos. Blocked the tunnel with a rag for the second attempt.
Day 3 - refitted the engine into the frame with the aid of 2 ratchet straps, a narrow bike jack and some wood.
I was well pleased with my self being a total novice and managing on my own.
Just want to ride it now.

 

[Oscar Meyer]

It sounds like you may have a vacuum leak or you have one of the carbs hanging up. When you had the carbs off the engine did the throttles snap shut if you opened the throttle with your fingers and then let it go? Did they all move freely? Are the intake rubbers in good shape? Do you have the proper clamps on the carbs? Were the carbs balanced (synchronized) properly? Are the throttle cables in good shape?

 

[Andy novice]

It sounds like you may have a vacuum leak or you have one of the carbs hanging up. When you had the carbs off the engine did the throttles snap shut if you opened the throttle with your fingers and then let it go? Did they all move freely? Are the intake rubbers in good shape? Do you have the proper clamps on the carbs? Were the carbs balanced (synchronized) properly? Are the throttle cables in good shape?

Throttles snapped shut when off the bike and moved freely, intake rubbers are not the best but I can not see any leaks when I spry them.
Not balance the carbs, need to learn how, Just adjusted the fuel mixture.
I don't think it is anything to do with the throttles as it does not do it when revved standing.
I will look at how to sync the carbs.
Any other ideas welcome.
Thanks

 

[Oscar Meyer]

Throttles snapped shut when off the bike and moved freely, intake rubbers are not the best but I can not see any leaks when I spry them.
Not balance the carbs, need to learn how, Just adjusted the fuel mixture.
I don't think it is anything to do with the throttles as it does not do it when revved standing.
I will look at how to sync the carbs.
Any other ideas welcome.
Thanks

If all 4 carbs are snapping shut properly then I would suggest getting the carbs synced up and do a bit more investigating into a vacuum leak. Crappy intake boots and wrong clamps can give trouble. Do you still have the vacuum operated fuel cutoff on it? They are nothing but trouble and should be eliminated.

 

[Andy novice]

Got sync gauges coming today so will test the vacuum sync.
Has anyone used the Color tune device to help with the fuel air mix screw adjustment?
I have found that I get a nice strong circulating bule color on 3 cylinders and hardly any thing on the 4th, even when I alter the fuel mix.
The cylinder is doing something as the engine dies when I unplug the spark plug.

 

[Oscar Meyer]

Has anyone used the Color tune device to help with the fuel air mix screw adjustment?

No I have never had the need to try one. If you have one cylinder different from the rest using your device then you could have a vacuum leak on that one carb or it is hanging open a bit. Get the carbs synced first and see what you get after that. I will ask again, do you have good intake boots and the proper clamps on all the carbs?

 

[Andy novice]

Did the sync yesterday and the suspect carb/cylinder was slightly lower than the rest, but only sightly. I adjusted it.
While the boots are old and the clamps on the air box side are jubilee clips they all seem OK to the eye. I have some easy start coming today which I intend to use for leak detection.
I will source some replacement boots and clips any way just to be sure.
I have not ridden the bike since syncing as the temperatures here are hitting record highs and it is just too hot to gear up.