Chain Tensioner Problem

[cvincer]

Decided to replace the front cylinder chain tensioner  to see if a slight noise would go away.

Retracted the (replacement) tensioner push bar, bolted unit in place, used a screwdriver to make the push bar push against the chain damper (i.e. the damper against the chain), fitted the spring & its retainer.

Pushed the start button, engine turned once & locked up.

Removed the chain tensioner, pressed against the damper with my finger & turned the engine over backwards & forwards
(socket on the flywheel retaining bolt via the little inspection cover) until the engine turned over without locking up.  Re-installed the chain tensioner (as detailed above), manually turned over the engine in a clockwise direction many times........ then pressed the start button.   

It's only firing on 1 cylinder,  I believe that the chain must have jumped a tooth.

Has anyone had this problem & worked out an easy quick repair?

.

[Jimustanguitar]

When I was reassembling my engine from a head gasket swap, I had the engine bind up a few times when I turned it by hand. Before you have the tensioner installed, it's easy to get an extra link folded up underneath the lower gear. It will bind on the crankcase and you can't turn it anymore. The fix for this is to pull the chain taught both on the in-feed and out-feed side of the gear while you rotate the engine a few times. This takes 3 hands, so you'll need help. I would definitely check that your timing hasn't skipped a tooth.

Unless your starter clutch seized or some other failure happened coincidentally, that's my best guess. Good luck!

[jefferson]

I bent valves messing with the gasket on the front cyl. tensioner. I think that is what you are going to find. It did the same exact thing when I tried to start it.

Jeff

[Rick G]

You bent 2 valves. The "easy repair "  is to pull the engine  and do a valve job on the head . Sunburnedaz will have several  serviceable used valves, He will probably be willing to sell.

[sunburnedaz]

You bent 2 valves. The "easy repair "  is to pull the engine  and do a valve job on the head . Sunburnedaz will have several  serviceable used valves, He will probably be willing to sell.

Yup. let me know if you do need them. I am going to be going though the parts pile over the next month to clean organize and kill any spiders the bug bomb didn't get.

[cvincer]

If the engine will turn over easily/without binding by hand (see photo),  can a valve be bent?

How would bolting in a chain tensioner (ensuring the tensioner push bar was pushing the damper against the chain before putting in its spring) ... have resulted in a problem?

Assuming the chain has jumped a tooth, need to work out a way to move the chain around on both the cam sprockets & the one deep in the engine ........ after doing nothing more than removing the cam cover followed by some fiddling.  I'll have to think through what 'Jim' said, perhaps it's applicable.

Apart from starter motors & clutches, over the years I've accumulated enough spares to make 3 engines; but with only a concrete pad as a workbench & after 12 years of kneeling on the concrete in front of this particular altar, I've almost had enough.

I have in mind the line from that  scifi  movie  'Bladerunner'             " a time to die"    (for the XZ)

.

[Rikugun]

I am going to be going though the parts pile over the next month to clean organize and kill any spiders the bug bomb didn't get.

Any particular kind of spider?  ??? Little black ones with red hour glass markings perhaps!??  :o  :(

If the engine will turn over easily/without binding by hand (see photo),  can a valve be bent?

Yes. There are other ways short of engine disassembly to determine if they are bent. You might try resetting the valve timing and performing a leakdown test to see if the valves are leaking.

[Rick G]

Black widows are OK
, But the ones to watch out for around here ,are the brown ones with corporals chevrons on the back!

[sunburnedaz]

Black widows are OK
, But the ones to watch out for around here ,are the brown ones with corporals chevrons on the back!

They were brown before I stepped on them. I squished two and said nope put all the boxes back in the trailer and went and got a bug bomb and set it off in the trailer no bugs seen since and now my garage has a slight bug bomb smell to it but I am ok with that.

[fret not]

It doesn't take much of a bend in a valve to cause leakage.

I would check the cam timing and make sure it is correct, then check compression or leak down test.  You may well just have just wadded the chain against the case and have no valve damage but a leak test will tell you all.

[pinholenz]

Blimey, I hope it isn't a bent valve. Good luck

[cvincer]

So I experimented with the spare parts engine.  With the cam tensioner out, it WAS possible to turn a cam & get the chain onto the wrong tooth.  Thought that replacing the cam tensioner somehow caused this to happen.

Took the cam cover off the problem installed engine, turned it over, & found that immediately after the inlet valves had closed, the exhaust valves open, very wrong.

With the piston at TDC the exhaust cam was in the position as shown in the photo, instead of the position shown as correct in Haynes (other photos).   Put cam/cog as it was supposed to be, & gave it a go.

It starts OK        idles well      exhaust noise is now quite a bit louder & of a bit different tone         no increase in vibration   ......  no blue haze out of the exhausts    slightly slower to 10,000 & less of a 'kick' at 6000.

I don't have a leak or compression tester & don't want to go through the hassle of taking it to bits again to see/feel/hear what difference moving the chain  1 tooth  will make.    As long as it gets me backwards & forwards into town, I'm OK.

[Rikugun]

Glad you got it going.  :)

So my understanding from this is you reset the timing and noticed these differences. Now you're not sure if the performance deficit is a result of bent valves or the timing is off one tooth, right?

[cvincer]

Yes .............. though with a bent valve, I will expect  rapid wear of the valve guides, resulting in oil burning, indicated by

a blue (2 stroke type) haze from the exhausts.

[Rikugun]

Not necessarily. They typically bend just behind the head leaving the guide largely unaffected. It may want to shift off center as it attempts to seat at each closing. This may increase "bell mouth" wear at the port end of the guide but the seals are at the other end.  Assuming you had no oil smoke before this happened, I can't see it being an issue now. At least not right away.  :(

Without some diagnostics tests to determine if they are indeed bent, you can never really know for sure. It sounds like your are satisfied it's running reasonably well and have little desire to tear it apart so hopefully it will be OK for you.  Let us know of any changes and good luck with it.:)

[sunburnedaz]

You can make up a quick tester if you have an air compressor and a blow pen with a big rubber tip. Turn the motor till its at TDC for the cylinder, remove the sparkplug then stuff that blow pen down the hole and fill the cyclinder with 10 to 15psi of air. If the valves are bent then you will hear the air rushing out the exhaust or carb.

[Rikugun]

That's a good suggestion but you may have to be creative in creating a tip that will reach the spark plug hole. On some, the tip threads into the blow gun with pipe thread. You can build an extension the right length with bits sourced from most hardware stores. I'd also suggest holding the crank in position via the rotor bolt and increasing air pressure to 80 psi.