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Discussion Starter · #1 ·
I am a novice as regards engine overhauls with general mechanical knowledge and experience. I had a V70 Tecumseh re-sleeved to standard bore. Everything looked spif and I re-assembled it myself and re-installed it in my 1972 JD 56. It started on the second pull and ran like new. However, after about 5 minutes the engine sounds as if it is taking strain and I kill it. It is then almost impossible to turn the engine. Once cooled down it again turns and runs normally but again wants to seize after about 5 minutes. The ring gaps were set at 0.015 (spec is (0.010 - 0.020). Any suggestions? Big end bearing perhaps too tight? I have the impression that its the piston that goes tight. Any advice will be appreciated.
David
 

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Discussion Starter · #3 ·
Wade, Yes, it crossed my mind too - that I have gone from aluminum to cast iron and the expansion will be different. I will try to look up the specs for VH70.

Thanks for you fast response.

David
 

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Discussion Starter · #4 ·
According to the Tecumseh Technician's Handbook (page 100) the only difference between the V70 and VH70 specs are the Crankshaft End Play(.005-.027 vs .003 -.031), Piston Diameter Bottom of Skirt (2.6212-2.6220 vs 2.7462-2.7437) and Piston Skirt Clearance (.0030-.0048 vs .0038-.0073).
So, my (layman's) interpretation: The bore and ring gaps of two (Aluminum and Iron sleeves) are the same but the piston of the iron engine is in fact 0.12-0.1217 bigger in diameter. The manual does not say how the piston skirt clearance is measured and I do not understand how this clearance is bigger (by 0.0008 - 0.0025) yet the piston is bigger in the same bore (2.75-2.751).

The VH piston in fact have less clearance than the V piston (.0048-.0073 vs 0.128-.1298).

Provided I have the right piston (for the V70) in there, this should not be my problem.

Any other suggestions? Otherwise it looks like another strip down to have the piston and bore measurements checked.

Apologies for my rambling on!
 

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Discussion Starter · #7 ·
Just to share: My brother, a farmer in another part of South Africa thought that I may have the big end too tight. When I re-assembled I did not have a torque wrench small enough to tighten the big end bolts so I added lock-tight to the bolt threads and tighten them to my best guess. Scared of causing damage if I keep running it for 5 minutes each time before it wants to seize, I have now pulled the engine to have a look. I have also purchased a small torque wrench and decided to test if I had the bolts over-tight. Well, I did not, and proceeded to tighten them to the recommended 24Nm. Then I could hardly turn the crank and decided to take the rod and crank out so that the engineering shop can re-check the tolerance. Unfortunately, as of tonight, I cannot get those two bolts loose! The 10 mm socket I use already started to slip. I have chissel-ed on the shoulder of the bolts but the little buggers still won't move. In the end I may have to sacrifice the rod to get the crank out of the casing for more space. Any suggestions how to get those bolts out, will be most welcome.
 

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Discussion Starter · #8 ·
I managed to get the conrod / big end bolts loose using a small pipe wrench. Hopefully, I can get the engineering company re-check the tolerance on the crank during this coming week. Today also dis-assembled the original V60 to have it checked. I already have both standard and oversize parts on hand. Sadly, Partstree.com won't ship me a std piston for the V70. They don't trade internationally and wants a USA credit card for shipping to a friend in Illinois. Hopefully they will eventually accept my Master Card as number of other companies do.
 
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