Rebuilding Johnson 70 hp

racerone

Supreme Mariner
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Dec 28, 2013
Messages
36,033
Rods are fractured when they are made.-----Caps will only fit on one rod and only one way.----match the dots and tighten rod bolts a bit.----They can / should be lined up perfectly.-----The rod in the second picture appears to be scrap to me.----Different part # on the crank is due to different / various seal arrangements on the splines for the driveshaft.-----Study those parts arrangements.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
That one rod is iffy and take a piece of emery cloth to the bridge in block. Sand just the bridge so it about .0005 bigger than bore measurement. Do water updates to block and prop it to the upper RPM range and it will be good to go. Rejet mains .002 bigger.
 

ZandoR

Seaman
Joined
Sep 5, 2016
Messages
57
Hi guys,

After waiting for 3 weeks on the machinist I'm back on it.
The guy from the machine shop told me that he would like to know the piston to wall clearance for the pistons, to decide whether to use a cutting bit or taking of the material with a hone.
Unfortunately the pistons didn't come with any specs (WSM cast pistons). On my internet search I found various numbers ranging from 0.002-0.007 inch.

I'd also like to hear your opinion on WSM aftermarket conrods vs used OEM ones. I spent enough money that I'm willing to go the extra mile to make everything as good as it can be, so I'm wondering if a fresh set of rods is a good idea?
I can get used ones for about half the price, but having trust in my motor is also important.

Thank you for your support!
 

racerone

Supreme Mariner
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Dec 28, 2013
Messages
36,033
Where did you find 0.007" clearance for fitting new pistons ?----And O/S pistons require boring !
 

ZandoR

Seaman
Joined
Sep 5, 2016
Messages
57
I think it was on PWC. Yes they need boring for sure. The machinist told me that the step from 0.030 to 0.040 over isn't that big. Because the top piston seized it did open up the bore a little bit already, so he said that, depending on the piston clearance, he would rather like to use a certain type of hone to carefully remove the rest of the material.

I hope that I translated this good enough for it to make sense. Anyways, it's not a regular automotive shop and he's done a couple of 2 stroke OB's, so I trust his judgement.

Does anyone have a spec sheet for the pistons or knows the tolerance?
 

racerone

Supreme Mariner
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Dec 28, 2013
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36,033
An example for you to think about and talk to the machinist about.------A motor with a standard factory bore is say 3.500 " and is worn out damaged.------A 0.020" o/s piston is fitted in a bore that is opened up to 3.520 "-----It is that simple.
 

ZandoR

Seaman
Joined
Sep 5, 2016
Messages
57
I understand what you mean and I thought about it the same way before he told me he needs the clearance. I guess he wants to measure the pistons individually to make sure he is doing the right amount. Maybe a good idea, should the piston have a different size than what it should have...
 

racerone

Supreme Mariner
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Dec 28, 2013
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??----Factory today make very good , accurate parts.---------Not the same as 75 years ago.
 

maybe368

Seaman
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Apr 26, 2005
Messages
67
I am pretty new to the marine world, but it seems to me that you would benefit much by having a set of both inside and outside micrometers. With them you can quickly answer some of the questions in this thread. IMHO, they are priceless for any mechanic. Do you have Harbor freight in Germany? If not, here is their online selection:

https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore,f,EAFeatured+Weight %2Cf%2CSale+Rank%2Cf&q=calipers+%26+dial+indic ators+%26+micrometers

​​​​​​​...Mark I hope that this is ok, I am not a lawyer and I read the terms and conditions and my untrained brain seems to think that this is not prohibited. I also checked and could not find any micrometers on the Iboats site...
 

ZandoR

Seaman
Joined
Sep 5, 2016
Messages
57
Hi Mark, you are absolutely right about that. I'm looking for them. We don't have Harbour Freight over here, but I guess there will be something on Amazon that will suit.

I checked with TSM Performance where I bought my rebuild kit and they recommended a clearance of 0.004'.
I will order new conrods soon, now that my block is still useable.

I'm also considering Chris Carson reeds, they seem to be a good choice for the big V6's, not so sure about the J/E tripples though…
 

Tim Frank

Vice Admiral
Joined
Jul 29, 2008
Messages
5,333
Micrometers are nice tools to have, but I am not sure that they are rquired necessarily by OP.
If his machinist does not already have a set of really good ones he might not be the best choice.... :)
 

ZandoR

Seaman
Joined
Sep 5, 2016
Messages
57
Hey Tim,

I will get a pair though to make sure he worked correctly haha :)
But to me it seems that he has a lot of experience with outboards, so I'm positive.
Can't wait to get her back together!
 

maybe368

Seaman
Joined
Apr 26, 2005
Messages
67
Hey Tim,

I will get a pair though to make sure he worked correctly haha :)
But to me it seems that he has a lot of experience with outboards, so I'm positive.
Can't wait to get her back together!

I once asked a machinist that had done an engine for me if he had any plastigauge for me. He was insulted and asked me why. I said that because I had seen the wrong bearings come in the new box. For example, a .020 over set in a standard box, he wasn't mad anymore and gave me some plastigauge that he had. I wondered why he had it, but didn't say anything. Everyone is capable of making mistakes and double checking is just an insurance policy, IMHO...Mark
 
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