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Forty40 10-23-2012 16:40:01 74.77.12.246 Report to Moderator	When boring a JD A Power Block is there a problem if the length of the bore is extended 3/16" deeper into the 45 deg chamfer (piston side) on the upper end of the block to accomodate a 1/2" longer stroke? Current piston to upper cylinder clearance is .137 and it would not appear the deck is substantially weakened since there is still over 3/4" T, stud depth does not change, and cylinder stiffness is not changed. Is there anything overlooked. [Reply]   [No Email]
Mike n Mo 10-23-2012 18:53:46 69.179.183.29 Report to Moderator	Re: Boring a JD Power Block in reply to Forty40, 10-23-2012 16:40:01   For an extra 1/2" stroke, you only need an extra 0.113" plus an extra 0.050-0.075 for clearance (given your current 0.137" you already have). Grind the piston to fit the bore, or have it turned in a lathe. The actual bore is offset from the upper cylinder area, so finish it manually if you want it to fit tight to maintain maximum compression (if that's your goal). Are you using standard bore "G" pistons? If so, they need to be turned down to fit even with stock stroke. Are you using stock length rods?. Lots of variables here, so can't give a prefect answer to your question. This post was edited by Mike N Mo at 18:57:18 10/23/12. [Reply]  [No Email]
Wilamayb 10-23-2012 17:48:26 66.168.153.148 Report to Moderator	Re: Boring a JD Power Block in reply to Forty40, 10-23-2012 16:40:01   I may be missing something here but how are you going to fit 0.50 extra stroke if your current clearance measurement is only 0.137? Maybe you have plans to obtain different pistons to allow for more clearance? [Reply]  [No Email]
Forty40 10-23-2012 19:24:11 74.77.12.246 Report to Moderator	Re: Boring a JD Power Block in reply to Wilamayb, 10-23-2012 17:48:26   Should say that I am not a JD or any kind of antique tractor expert/mechanic for that matter. My experience is completely different with circle track engines for the past 35 years so the two worlds may not meet as directly as I anticipate. Since we regularly use welded, heat treated, and re-ground crankshafts in 8000 RPM applications, the plan was to send the standard JD A crank to the crank shop, weld the pins, and regrind to a std 3.000 pin with a 7-1/4" stroke. If the underside clearance can be increased in the cylinder block by 3/16", a standard rod and std pin height piston could be used. The plan is to bore to 6.125 using an oversized but std pin height Power Block piston. Looking at the head, we equalized the intake runner to each valve and estimate after valve unshrouding the head can be milled to around 135 CC combustion chamber volume. Havne't used the burrete tube yet to find actual CC volume. There's quite a ridge to remove to unshroud the intake so volume is only a guesstimate using a caliper and calculator. With a reduced total combustion chamber volume this would give an 8.5:1 compression ratio. The guys that grind our racing cams also grind cams for tractors, so the cam will be changed. Not really a total all out performance plan and nothing compared to a 15:1 race engine, but the objective is to increase performance and still use pump gas. For this 60 yr old tractor I didn't really want to make an all out puller and have to use racing fuel. Our VP Late Model Plus is over $11/gal which I thought was a little high to putt around. [Reply]  [No Email]
wilson ind 10-25-2012 15:06:46 70.239.85.115 Report to Moderator	Re: Boring a JD Power Block in reply to Forty40, 10-23-2012 19:24:11   I would like to know how to add lobes to a crank on a briggs engine. want lobes like 2 cycle to make steam engine Just pet project I always wanted to do Thanks e mail is open [Reply]  [No Email]
forty40 10-25-2012 17:02:37 74.77.12.246 Report to Moderator	Re: Boring a JD Power Block in reply to wilson ind, 10-25-2012 15:06:46   It"s been many years since we have had a two stroke engine apart, but as I recall, they have circular counter weights and not lobes as a 4 stroke would have. If a briggs crank is steel, then it can be welded with ER70S-3 using the tig process. Adding counter weights in a way so the new metal surrounds the existing crank lobe and would be mechanically locked in place by an overlapping fit. Simply welding a piece on the outside of the existing counterweight location would be doomed to failure and could be quite dangerous if it flew off. Do not stress the weld in tension or bending by the centrifigal force during rotation. That"s the easy part. Crankshaft repair is part science and mostly art based on past experience. I"m not the crankshaft repair guy and use a shop that specializes in shaft repair. Bracing during welding, welding sequence, preheat, straightening, stress relieving, and heat treating are all part of the process and may have to be repeated through the heating straigtening cycle more than once. Some shafts and stems are hot straightened some are cold straightened. There some pictures on the Allshaft Repair Facebook page that shows a DT466 counterweighted which is probably similar to what you are trying to do, except on a much smaller scale. [Reply]  [No Email]
Wilamayb 10-24-2012 04:55:55 66.168.153.148 Report to Moderator	Re: Boring a JD Power Block in reply to Forty40, 10-23-2012 19:24:11   I say let it rip then! Sounds like a plan to me. Your compression ratio should work fine. Many pullers get it too high which causes the engine to lose the ability to lug. They fall flat on their face after being pulled down to a normal rpm range. Yours should still run with lots of ponies in the stock rpm range. [Reply]  [No Email]
BushogPapa 10-23-2012 19:56:14 173.88.51.117 Report to Moderator	Re: Boring a JD Power Block in reply to Forty40, 10-23-2012 19:24:11   Many use higher compression and E-85 for fuel and it works well... Ron.. [Reply]  [No Email]