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Old 12-06-2013, 20:36   #16
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I only have experience with old motorcycle engines but from the sound of it you may just want to run the hone once or twice if only to aid the new rings to seat. One concern being if you run your finger up the bore and can feel a ridge at the top of the stroke from the old rings travel. You may want to get rid of that as it may cause issues with the seating of the new ones. Lacking a real shop I would think fiddling with it further is asking for troubles.

I don't think it is as big a deal at the bottom of the stroke as that is just a sweeper ring and not a compression one. Of course I may be off on your ring setup as I don't know it specifically.
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Old 12-06-2013, 20:51   #17
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Re: To hone or not to hone old yanmar

Your guy there is no doubt resourceful but you need to hone it. It takes quite a bit of honing to remove much material. If you don't hone the cylinder you run the chance of scuffing the cylinder wall in a bad way. Perhaps he does not have a hone or after 10 ovhl's you would wear it out.
I would weld a gas engine piston but not a diesel.
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Old 12-06-2013, 21:35   #18
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Re: To hone or not to hone old yanmar

why does your mechanic say no hone? No offence to the opinions listed above but i have seen some fantastic engineering done in Asian shopfront machine shops - your guy might know what he's talking about...and theres a sting in the tail of taking all the contributors on this forum's opinions with the same weight...some are very good, some consistently bad...
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Old 12-06-2013, 21:40   #19
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Re: To hone or not to hone old yanmar

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Aside from the dirt it looks OK, nice lathe.. You could make a glaze breaker out of some sand paper and a drill, kind of a flapper wheel hone. It might be better than nothing. You do have new gaskets right?
Hello Guy:
You should be in this place sometimes ! See the things that are done, it is jaw dropping.
I have read a bit more on the subject, and I am leaning towards the "If it aint broke, don`t fix it" as I do not have the tools here to properly diagnose it and fix it.
I can tell you, it runs great, does not smoke, starts in a second every time, has minimal blow by from the crankcase breather, runs strong, has good oil pressure...
I agree doing it right is the right way...
The reason this issue came up, was because I am planning a new engine purchase in three years and wanted to be sure this one would go that distance. I pulled one head and one rod, just to have a look....Now that I see the importance of their being some cross hatching left, I will go back and pull another head and really examine the bore surface.
It is a given that it is out of round, 30,000 hours and it had better be, but it performs well. If I start messing with it, I may introduce a host of new problems.
I will do the big end bearings in any case, though they are just starting to show copper spots.
There have been a variety of opinions offered here, considering that it runs well..what do you say..if it aint broke, don`t fix it..especially if you cannot determine how badly it is worn ?
Changing the rings will not impact me, until they actually fail.(Unless one breaks) I will have some smoke, more blowby...but the boat will run.
I risk making the boat unusable by fiddling with the rings.
Opinions please ?
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Old 12-06-2013, 21:44   #20
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Re: To hone or not to hone old yanmar

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Originally Posted by charliehows View Post
why does your mechanic say no hone? No offence to the opinions listed above but i have seen some fantastic engineering done in Asian shopfront machine shops - your guy might know what he's talking about...and theres a sting in the tail of taking all the contributors on this forum's opinions with the same weight...some are very good, some consistently bad...
Hello Charlie:
So you have spent some time here, you understand !
Of course I expect different opinions, I think my conclusion to leave it alone for now is the correct one, after all it works !
Why go looking for trouble that could bankrupt me ?
This link was helpful.

Bore glazing
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Old 12-06-2013, 21:58   #21
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Re: To hone or not to hone old yanmar

79 yanmar 2qm20, never had the heads off, i take care of the anodes, oil changes, keep the rust off as much as possible, keep the fuel clean, impellers etc, if it aint broke dont fix it is my mantra...
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Old 12-06-2013, 22:10   #22
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Re: To hone or not to hone old yanmar

I guess I'm confused, I thought you had it all apart? If the pistons are still in the cylinders and it had been working fine why is all this coming up?
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Old 12-06-2013, 22:23   #23
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Re: To hone or not to hone old yanmar

Ya know Ive made my living in shops like the one shown on here! I can't imagine there being no measureing equipment there ! In fact I see some laying around in the pics! Sounds like your makeing things up a little maybe?? LOL heck with the type of diesel your talking about you should be able to fix it with a crescent wrench and a BFH and a couple of big screwdrivers !! Heck if it's still together leave there and go somewhere with a BIG shop and get it fixed ! Just my 2 cents
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Old 12-06-2013, 22:29   #24
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Re: To hone or not to hone old yanmar

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I guess I'm confused, I thought you had it all apart? If the pistons are still in the cylinders and it had been working fine why is all this coming up?
Hello Guy:
I think you do not quite appreciate how big 100 h.p. was in 1979.
The engine weighs about a ton. There are access doors to the big ends.
I can pull a piston and rod in about 30 minutes...I can pull one of the six heads in about 25 minutes. Sorry I was not more clear..
This is a photo.
Pull the rods in place, engine in the boat.
Valve cover gaskets are rubber seals. Head gaskets are made to order. Yup head gaskets.
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Old 12-06-2013, 22:33   #25
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Re: To hone or not to hone old yanmar

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Ya know Ive made my living in shops like the one shown on here! I can't imagine there being no measureing equipment there ! In fact I see some laying around in the pics! Sounds like your makeing things up a little maybe?? LOL heck with the type of diesel your talking about you should be able to fix it with a crescent wrench and a BFH and a couple of big screwdrivers !! Heck if it's still together leave there and go somewhere with a BIG shop and get it fixed ! Just my 2 cents
Hey Bob..
Calipers...we got loads of those.. I have never seen a mic on the island.
Except in my dive shop, where you will find the only torque wrenches on the island as well.
No smoke blowing nor whistling dixie or waltzing matilda here....this is an isolated island in the south china sea, with a population of 3,500. There are 30 cars here. Internet 1/2 the time. Electricity has gotten more reliable and it is good about 50% of the time.
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Old 12-06-2013, 22:46   #26
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Re: To hone or not to hone old yanmar

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Originally Posted by bobconnie View Post
Ya know Ive made my living in shops like the one shown on here! I can't imagine there being no measureing equipment there ! In fact I see some laying around in the pics! Sounds like your makeing things up a little maybe?? LOL heck with the type of diesel your talking about you should be able to fix it with a crescent wrench and a BFH and a couple of big screwdrivers !! Heck if it's still together leave there and go somewhere with a BIG shop and get it fixed ! Just my 2 cents
Hey Bob..
I think you understand the nature of this engine ! This is a hardcore serious marine heavy duty beast. That is how they fix em, with a BFH.
run at 1,800 rpm, we run it at 90% of full about 3 hours a day for more then an hour at a go. It has a PTO at the front for a hydraulic pump to pull up fishing nets.
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Old 12-06-2013, 23:48   #27
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Re: To hone or not to hone old yanmar

Yeppers, Ive fixed a couple of those sweeties a time or 3! Will run forever, and burn little fuel doing it !! I would sure wait till I could get somewhere else to fix it ! To good an engine to take a chance, might change the rod bearings if I had some LOL and do the rest includeing the mains at a better equiped shop LOL Im sure she will get ya where ya want to go !
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Old 13-06-2013, 01:37   #28
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Re: To hone or not to hone old yanmar

Hello Bob and everybody
With the engine running as well as it does....
I think you are onto something, there are very probably better equipped machine shops in Vung Tau, 200Km from here on the mainland.
I will go and take a look.
Parts will take a while to source, but if I am gonna spend $20,000 + in three years on the new engine....and it will lays up the boat for 2 weeks, changing shafts and doing all the diddeling around with it...
I may as well do the big ends, leave the rest alone and run it up to Vung Tau....turn it over to them.
I will probably have a good as new engine for around $4,000....Labor is cheap here.
I have been looking for a core to send to Saigon to do just this with, but having little luck.
Thanks everybody for the input, the debate and discussion has been enlightening, I have learned a lot.
I also think I have arrived at the best solution for me.
Oh, and the first plastiguage on the island was brought here by me.
As were the first automatic bilge pump switches, and the first demand pressure pumps !
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Old 13-06-2013, 04:08   #29
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Re: To hone or not to hone old yanmar

You can measure the bore variations by placing a piston ring squarely at the very bottom of bore (square it with piston) and measure the ring gap. Move it up an inch at a time , measuring each time. If there is a large variation you have problems.
You should also try to measure your big end journals for ovality, if they are oval you are wasting your money just replacing the shells.

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Old 13-06-2013, 04:27   #30
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Re: To hone or not to hone old yanmar

Hello Richard...
Point well made.
Lets see.....no micrometer..fly to Saigon to buy one, open engine to reveal out of round big ends or crank journals...oh man....I am gonna get me a core and have it rebuilt in Thailand and send it back over here...
I have been thinking about how things are done even in the best shops in the country..scary. My wife is a dentist, was the clinical manager for the biggest group of western owned dental clinics in the country, and she had to put up with third rate dentists while charging nearly western rates...people here know absolutely nothing...If you saw the Yanmar office in Saigon you would cry. I cannot believe the company allows this as their representative office.
"Skilled" and "Labor" cannot be used in the same sentence together here.
I was nearly out of my head when they were building the boat. Building in flaws that were sure to sink it, and not understanding where they were going wrong..plastic sea cocks, with plastic hose running ON THE FLOOR to the water pump">raw water pump....
No, not going there again....
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