Where to start - putting it back on the road

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PaulGreen
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Re: Where to start - putting it back on the road

#166 Post by PaulGreen » Sun Dec 16, 2018 7:27 pm

As I mooched around on the internet looking at another rebuild project, I think I'm fairly sure that I used non gem gaskets. I think I used vesrah(?) gaskets.
I'm going to struggle to get hold of another comp tester without buying one, and the only other petrol engine I've got access to to test the one I bought us my wife's A class Mercedes. And to get access to the plugs on that you need to be an 8 year old contortionist!
Having said that, my options are limited, so I'll get the yoga mat out and have a go. When it stops raining.

lost1750GTV
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Re: Where to start - putting it back on the road

#167 Post by lost1750GTV » Sun Dec 16, 2018 8:49 pm

your numbers are equal, go back to carbs/ignition before thinking about anything else.

silverstrom
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Re: Where to start - putting it back on the road

#168 Post by silverstrom » Sun Dec 16, 2018 11:23 pm

lost1750GTV wrote: Sun Dec 16, 2018 8:49 pm your numbers are equal, go back to carbs/ignition before thinking about anything else.
Yes, and 80 PSI lower than they should be. If those numbers are right, all the carb and ignition work in the world won't matter.

lost1750GTV
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Re: Where to start - putting it back on the road

#169 Post by lost1750GTV » Mon Dec 17, 2018 12:35 am

"the same monumental mistake on all 4 cylinders"
hard to do that so well, and it was running on 2 (+)? and that's not the same, and points to something else.
I think the numbers problem is in the testing.

silverstrom
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Re: Where to start - putting it back on the road

#170 Post by silverstrom » Mon Dec 17, 2018 3:27 am

lost1750GTV wrote: Mon Dec 17, 2018 12:35 am "the same monumental mistake on all 4 cylinders"
hard to do that so well, and it was running on 2 (+)? and that's not the same, and points to something else.
I think the numbers problem is in the testing.

Yes, that does seem likely, but I do think that it still needs to be verified. With the aftermarket head gaskets and the heads being off and on it remains a remote possibility. If it isn't addressed it will just be an unanswered question if carburetors are not the cause. It seems unlikely to be ignition related at this point, unless there is an issue with the flywheel itself, such as one of the magnets. One step at a time, and logic now dictates that the first thing to address is the compression issue. Once it is verified as good then go back to trouble shooting and fueling as a possible cause. It would really suck if this goes back to the lock up of the rear crank being a contributing factor and the crank being out of phase.

silverstrom
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Re: Where to start - putting it back on the road

#171 Post by silverstrom » Mon Dec 17, 2018 3:44 am

I just went back to the start of this thread. This engine had many crank rebuilds over a relatively short period of time, which does seem a bit unusual. Was there a reason for this? I ask because whenever cranks need constant rebuilding I find myself asking if the upper and lower engine cases are actually a matched set.

PaulGreen
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Re: Where to start - putting it back on the road

#172 Post by PaulGreen » Mon Dec 17, 2018 5:45 am

Is there any way of knowing for sure if the engine cases are a matched set?
This has been mentioned before but I found nothing to suggest they weren't.

One thing that I know for sure that wasn't by the book was taking the heads off last week and not replacing the gaskets with new.

When I rebuilt the engine 6 years ago I would have checked and measured for tolerances, and when I had the rear barrels off recently you could still see the honing marks on the bores.
It's the uniformity of the low readings that bothers me.

Maybe I'll whip the top end off and recheck everything and get new gaskets.

Paul

silverstrom
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Re: Where to start - putting it back on the road

#173 Post by silverstrom » Mon Dec 17, 2018 3:36 pm

The numbers are scratched into the cases. The numbers mean nothing specific. Their only purpose is to identify a matched set of cases. The crank journals are line bored and matched sets must stay together. If you have an unmatched set you can run into problems with the crank binding, killing bearings, etc.

silverstrom
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Re: Where to start - putting it back on the road

#174 Post by silverstrom » Mon Dec 17, 2018 3:57 pm

When you had the heads off did you tighten the nuts in the proper sequence and in 2 stages?

PaulGreen
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Re: Where to start - putting it back on the road

#175 Post by PaulGreen » Mon Dec 17, 2018 4:44 pm

I vaguely recall seeing some etchings like that, sadly I feel they won't be visible any more as I had the cases head blasted some time ago. I'll certainly have a look though. To save my eyes from too much strsining, Do they tend to be in the same place?
I've got some photos of the black painted cases, too, so I'll look through the archive for clues.
The heads, as with all mated faces, have always been tightened in sequence and over a number of passes, at least under my ownership, so that shouldn't be the cause.

Thanks for the continued input here,
Paul.

lost1750GTV
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Re: Where to start - putting it back on the road

#176 Post by lost1750GTV » Mon Dec 17, 2018 5:36 pm

in the coil thread, it was "running on 4 for a while' - that was saturday.

PaulGreen
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Re: Where to start - putting it back on the road

#177 Post by PaulGreen » Mon Dec 17, 2018 6:19 pm

It was, as I opened the throttle it ran very briefly on 4.
It ticks over on the front 2 with an occasional ignition from the upper right.
As I opened the throttle, gently, they all came on together for a few seconds, but it would maintain 4

Regarding mismatched cases, I've found the numbers. They're very, very faint. I'm 99.9% certain that they're ok. The last 3 characters are E04, the first one on the top half is an angular 8, the bottom looks like a Z but I'm thinking that some of the original 8 was erased when it was bead blasted.
Looking at silverstroms photo I can see how that could have happened.

I'm hoping to get my hands on somebody's car tomorrow so I can test my compression tester.

Cheers,
Paul.

silverstrom
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Re: Where to start - putting it back on the road

#178 Post by silverstrom » Mon Dec 17, 2018 6:46 pm

Your cases are fine. Could it be that all those past crank rebuilds were the result of youthful exuberance and getting maximum enjoyment from the engine? :mrgreen:

Perhaps, as lost1750GTV says, it will all come back to carbs. If it did try to run on all 4, even briefly, that eliminates most serious possibilities. It is unlikely that compression is 45, but it would be nice to know that it is somewhere close to normal, just to have that on record.

I would look at the gap on the pick-up coil as that has been known to be the source of non-running issues. If that pick-up gap is too large you will have very weak spark or no spark and the engine will never run. It is usually the simplest things that cause the biggest headaches.

PaulGreen
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Re: Where to start - putting it back on the road

#179 Post by PaulGreen » Tue Dec 18, 2018 7:49 am

This morning I've managed, in a very rudimentary way, to prove my compression tester. Using a track bike pump sealed over the comp test input I managed to get roughly 100 psi on both gauges.
Unfortunately this shows that my compression is way down so the top end is coming off. Again.

Any recommendations for top end gasket kits? Or is it gen Yam gear only? Assuming you can still get genuine?

Cheers,
Paul.

PaulGreen
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Re: Where to start - putting it back on the road

#180 Post by PaulGreen » Tue Dec 18, 2018 8:03 am

That was easier than I expected. found a gen top end set on eBay for GBP 160

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