TOPIC:

Long story short but my mechanic is screwing me.

My 79 cylinder block has been bored out and the head has been cleaned up. Ground the valves and seats, new o-rings, mild polish.

My 79 bottom end is a mess and in pieces. I do not want this guy to do any more "work". He refuses to do anything I ask in timely fashion and at this rate my bike won't be ready until next year.

My 81 was working fine until another mechanic put my starter clutch in and it never ran again. Very low compression in all cylinders. One was below 30.

Can I use my rebored and rebuilt top end on top of the 81 bottom end, or does the different timing set up not allow it?

If so, can I put my 81 engine with the 79 top end in my 79 frame or do the different ignition systems make this difficult. If so, can I put my 79 body parts on my 81 frame?

I am close to abandoning this project and I really need some advise.

Thanks

Whoa Whoa Whoa Ledkz, my best advise to you is firstly before you start chopping or changing bottom ends blocks anything like that is take a step back gather breath and think. Firstly you have determined you have low compression, find out why. It could be and probably is due to work having been undertaken on this area of the bike that your timing is incorrect ie crank and cams not correctly timed, this will cause low compression along with huge starting problems. You can kill 2 birds with one stone here as your cam cover has to come off. Firstly check your Crank and Cam timing is exact as shown in the manual others on here can further advise along with myself, if good you can then check your valve clearances ensuring they are correct and valves are not being held open impacting on your compression. I will say no more at this stage but strongly advise that this is where you start with your fault finding. If your bike was working fine before a shit mechanic got his hands on it then no reason it shouldn't work going forward. But don't give up take phot's and post on here there is an awful lot of knowledge amongst all. Ignition timing we will talk about later when your compression problem is solved

its easy to check the valve timing, remove the generator cover Right hand side and set the crank to TDC
theres a DOT on the sprocket of the exhaust cam, it should be level with the surface to the front of the cam.
if the DOT starts in the middle of a plate on the chain that plate is the 1st. count 17 plates and you should have a second DOT on the inlet cam
IF THE DOT STARTS IN THE GAP BETWEEN TWO PLATES THEN THE DOT IS THE 1ST GAP COUNT 17 GAPS
a third DOT should be to the rear of the inlet cam sprocket level with the surface
if you get a workshop manual the pictures explain it a lot better than i have.
you can download a manual from the home page.

valve timing page 67

Thanks for the responses fellows.

Sadly, it is not that simple. In the process of deciding I wanted to use the 79 engine and frame I've already taken parts off the 81. Carbs, airbox, brakes, forks .... simple stuff. But that isn't the big problem.

The 81 definitely has to have the head removed because the cam chain gear is worn out as is the cam chain tensioner. I found that out when I removed the cover and shone a flashlight down inside. The teeth aren't stripped but they aren't far from it. Maybe this is why it lost compression but how weird is it that it was running great before he put his hands on it? What are the odds? Once I determined that it was a problem in and of itself I found the 79 which also ran... very well actually except for it smoking like a train.

I spent a lot of money getting parts so far for the 79. New cam chain gear, as well as new timing advancer gear and new timing advancer because he broke both of them taking the 79 apart. I've paid the machinist to bore the cylinders and the head has had the valves and seats ground, new o rings etc. I really don't want to waste all of that money.

The problem is I am not a mechanic. Not even close. So I have had two different mechanics doing two different things and between the two I am sitting on a huge pile of crap and wasted money unless I can go forward with at least putting that head, cylinders and parts on one of these.

I have a friend who is willing help me do what I need to do. He has the tools and far more mechanical knowledge than I have. He says as long as I have the manuals, which I do, that we can figure it out.

What he doesn't want to do is try to reassemble a bottom end that he did not take apart. He would have been comfortable doing it if he has taken it apart but he didn't. My asshat mechanic has stripped the bottom end completely right down the transmission being in pieces. I'm pretty sure he didn't bother numbering the rods either when he took the crank out.

So... can we take the good 79 top end, put it on the 81 bottom end with my new pistons and freshly bored cylinder or are they incompatible? Can I put the 81 engine in the 79 frame after we are done or do I need to swap all the parts I took off it back over?

the only issue i can think of is the ignition on the barrels.
i think everything else is the same.
you could always get your liners pressed out of one set of barrels and pressed into the other set and get them gently faced
no swapping around needed then.

I feel your pain and frustration but I have to say, the road to restoration of 35 year old motorcycles is not as simple as tear it apart and replace the worn out pieces and down the road for another 50,000 miles. You've hit a couple of set backs on 2 motorcycles and maybe if you were dealing with just one then you'd be pissed but not ready to throw in the towel.

My suggestion would be to put the 79 off to one side for now and focus on the issues with the 81. It would seem that the chances of repairing the 81 at this point would/should be easier than trying to resurrect the 79. The work on the starter clutch shouldn't have caused the low compression unless by chance the camshaft timing chain was loose and it jumped a tooth. If that's the case, there's a strong possibility that there's a bent valve. You need to verify the valve timing.

I think maybe if you get the 81 running, it will help you find the patience to ressurect the 79. The engine's are not that complicated to work on, but you have to have patience when doing it for the first time. the service manual should suffice for the most part. i would also suggest you go to a site like Partszilla and get yourself exploded views of the parts for reference. That way you can verify that you've got all of the required pieces and put them in the right places.

If you've been following along with my build out of a 1980 you know that I too have been having my share of moments. Sent out a set of camshafts for grinding and the shop completely F....Ked them up. Now I'm looking for primary and secondary chains that are not Chinese and I've been trying to source all over the world with little success. For me, this project is a labour of love. If it takes me 10 years, so be it. The fun for me is overcoming defeat. I won't give in or settle for half best. Life is about the journey, not getting to the destination.