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type IV engine refresh conundrum...
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TrollFromDownBelow
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PostPosted: Tue Jul 10, 2018 7:47 pm    Post subject: type IV engine refresh conundrum... Reply with quote

Long story short...have a really good running bus - smooth, not flogging it to keep up with traffic, will do 65-70 (real speed) all day long. But...one head has a broken exhaust stud...ergo, not fixable. Other head has a healicoil of unknown origins that has a death grip on the plug; I've put 20k on that plug myself (bought the engine used...no telling how many miles on the plug), and it's down to the nubbins. I checked compression about 10k ago, and it had 110-118 on the three cylinders I could check (sans helicoil cylinder). It's always been a bit thirsty for oil. about 300 miles per quart interstate and 600 or so city.

Got tired of the noisy exhaust, and finally broke down and bought a set of Len's heads Smile.

Took the engine apart last week, and based upon pooled oil on the jugs and slightly washed off carbon on the piston, I've got blow bye issues.

Complete tear downs is not in the cards right now, mainly due to time constraints (short summers here in Michigan, still want to get some use out of it this year), and, as I only put a couple thousand on it a year, if I can get it to go another 15-20k miles, that's a good bit of time.

My theory is, if I re-ring and hone the cylinders I won't disrupt the inherent balance/homeostasis of a nice running engine, and will probably get another 20k.

Alternatively, I could put new pistons and jugs on it, although it may run phenomenally, as I won't be able to balance the assembly, I'm concerned that it will start beating things up internally and I will have even less time before a total rebuild.

Goal is to get as many reliable miles (oil burning be damned) in it's current state before having to do a total rebuild.

Bottom line, which option is more likely to give me more miles before I have to crack the case apart?
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busdaddy
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PostPosted: Tue Jul 10, 2018 8:58 pm    Post subject: Re: type IV engine refresh conundrum... Reply with quote

Photos of the bores with the pistons down at the bottom of thier stroke would help decide, and measurements of the piston and ring land clearance.
How was the oil pressure pre teardown? How long did it take for the oil light to come on after you stall it when warm?, what weight oil were you running?
What's the endplay like?, how do the lifters and cam lobes look?, what does it look like down the breather tower?
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Wildthings
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PostPosted: Tue Jul 10, 2018 9:04 pm    Post subject: Re: type IV engine refresh conundrum... Reply with quote

What does your cam look like? If the cam and lifters are badly worn then nothing you do to the rest of the engine is going to give you a long lived engine.

I doubt you will end up with more cylinder taper than the POS engine I have in my Bay presently. I have about 20K miles on it since I honed the cylinders and replaced the rings and it runs as well as can be expected with a sad excuse for a cam. I figure it will give me another 20-40K miles before the pistons decide they have had enough.
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raygreenwood
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PostPosted: Tue Jul 10, 2018 9:35 pm    Post subject: Re: type IV engine refresh conundrum... Reply with quote

Wildthings has noted the most critical issue.

As for cylinders....honing and new rings...whether its just a new cross hatch with a FlexHone....or a rebore on a machinem...are NOT simple work.

I would have at minimum....a good basic valve job done if you have no cracks.....and pjt ib real inserts and post about it because we can help you do better than a helicoil.....and buy a new set of cylinders and pistons.

Also.....the piston balance unless they are grossly off......are the least of the balance issues. If you are leaving the bottom end alone....and assuming the end for end balance on the rods is ....ok......asong as the pistons are not more than a gram out each from the old pistons.....just reuse the old wrist pins in the same position. Ray
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Spike0180
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PostPosted: Wed Jul 11, 2018 5:04 am    Post subject: Re: type IV engine refresh conundrum... Reply with quote

raygreenwood wrote:
Wildthings has noted the most critical issue.

As for cylinders....honing and new rings...whether its just a new cross hatch with a FlexHone....or a rebore on a machinem...are NOT simple work.

I would have at minimum....a good basic valve job done if you have no cracks.....and pjt ib real inserts and post about it because we can help you do better than a helicoil.....and buy a new set of cylinders and pistons.

Also.....the piston balance unless they are grossly off......are the least of the balance issues. If you are leaving the bottom end alone....and assuming the end for end balance on the rods is ....ok......asong as the pistons are not more than a gram out each from the old pistons.....just reuse the old wrist pins in the same position. Ray


He bought new Len Heads.

I don't think it would make much of a difference. If you buy new pistons, get your hands on a good food scale and make sure each piston is the same weight as what came off the engine. If not the same as what came off, then at least make them equal to each other. Or just hone and rings, slap it back together and go back in this winter. Either way, make sure to glance at your cam lobes for wear. Likely they are worn if it wasn't a recent rebuild.
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my59
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PostPosted: Wed Jul 11, 2018 3:44 pm    Post subject: Re: type IV engine refresh conundrum... Reply with quote

If you already have the engine out, the heads off, and willing to do new P&C, then review the cam and as they say, in for a penny, in for a...rebuild.

Dunno what your work space is like, but a rebuild in my barn in the summer is very preferable to the rebuild I did over the winter a few years back, no heat, layered up, and moving parts from the barn to the basement to do measurements, figuring parts at 30 degrees will be different than parts at 68 degrees...

The cam wear was pretty spectacular, the lifters were dished and the engine had almost 0 oil pressure before it was pulled.
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Tbob
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PostPosted: Wed Jul 11, 2018 7:29 pm    Post subject: Re: type IV engine refresh conundrum... Reply with quote

I feel your pain. The midwest with it's 4 seasons (June, July, August and Winter) make it hard on car hobbists . You either have time to work on it or drive it before the next winter. I also understand your dilema, you had a good running bus with head issues that were secondary to proper combustion events. So new heads, and re ring and hone, should be able to get you another 20,000 miles, right? Re read Bus Daddy's post . If you had good oil pressure before teardown, and your endplay was within range (both indicators of an ok bottom end), if your cam and lifters are ok(Highly unlikely), then I would pull the oil pump and make sure the idler shaft hasn't migrated toward the cam, Also check that the cam rivits are tight, and that the cam doesnt have excessive end play, indicating a bad thrust bearing. If all checks out well, then check the cylinders and pistons carefully, as a quart every 300 miles is a lot of oil usage. New pistons and cylinders may be warranted. You may get lucky, and be rewarded with that 20,000 to 30,000 miles you are hoping to get.
Although my old Fords will run an amazing amount of time with really make do repairs, our air cooled engines do not seem to be as tolerant of partial repairs.
A few years ago, I pulled the engine on my 73 to do a clutch. I was taught to do a simple compression test before pulling any motor, and cyl #3 was 75 lbs where all others were 120-125. I found a bad head gaslet, and almost would have put the engine back together except when I spun the reassembled long block around on the engine stand, I heard the unmistakable sound of a loose piece of hardware rattleing around in the case. So, I took it all apart. Never found the source of the sound, but i did find the oil pump idler shaft hitting the cam, and almost wearing the heads off the rivits, the distributor drive had too much play, and one of the cam bearings was eroded.Of course, the cam and lifters were shot. Like you, my engine ran great, and smooth. But it was a time bomb.
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