Engine rebuilding 101

#1

I have the tools, the skills (I think), and maybe I can find the time to do it but I have never rebuilt an engine before. Well, I don’t think I can count a 2 stroke dirt bike engine. I need some guidance from those of you that have real experience with this.

I know several of you have had "professional" rebuilds lately to the tune of $3k to $4k. How does this compare to the other people who say they "freshen" the head and rebuild the lower end for much less money? What’s the difference?

I guess I should start with a compression and leakdown test to see where my problems are. The reason I am even considering this is because I’m down on power, 147HP/145TQ. Thanks for any insight.

#2

Ken - I can only relate our experience with a rebuild. IIRC those who have the $3-4 rebuilds also paid for labor for the swap.

We spend about $1250 on our late summer rebuild following the bearing failure at VIR. We had the head freshened for $250. Bought a new engine/head gasket/seals set, new water pump, timing belt, crank scraper, new head bolts, new clutch kit - about $600. We used the bottom end from the donor engine as is. We were quoted $600-800 to rebuild the bottom end but decided to leave as is (donor motor was $500). Our advisor/mechanic Dave P. said you can do it yourself (replace bearing, etc.)but it hard to get it right (using plastigage, etc) so this is best left to the pros. We did all the labor ourselves - not that difficult if you have an engine lift and stand. It took us 2 weekends - first to remove - second to reassemble/install. Our motor made good power at Mid-Ohio. So it really depends on how much you want to do yourself on how much you spend. Best of luck.
ed

btw - you can install the engine and transmission together with a little patience.

#3

Ken…Stop, you’re not too far off on power. I drove the 8 ball at Roebling and it was at 140tq and 145hp. Call me and I can give you some things to check and possibly save you lots of money.The 8 ball was fixed with a new oxygen sensor. Let’s make sure that you’re getting all you can from what you have.

By the way, youv’e done it the right way, starting out with baseline numbers before turning the first wrench.

Regards, Robert Patton 800-755-1715

#4

Ken,
your numbers are not terrible…Do a leakdown test (if you do that I don’t see a point in doing compression test) but make sure you do it right. I would suggest doing it with engine warm so that ‘things’ can expand and seal as during normal operation

#5

Thanks for the suggestions. I don’t think the numbers are that bad unless you compare them to the fresh engines at VIR last summer making 160+ hp/tq. Truth be known I could spend a little more on making the driver better and improve my laps times by more than a rebuild. I will have a leakdown test done and see how it looks and let you know.

#6

I rebuilt the engine in my car last winter. We went low buck; left the engine in the car pulled the head and dropped the pan and just put fresh bearings (rod and mains) and re-ringed it (crank and cyl walls looked good so we left them alone and used factory sized stuff). also replaced all the wear items (oil pump, water pump, timing belt, etc…). Overall it runs strong I don’t have any dyno numbers (still in DE land) but I have about 150-160-ish psi on the leak down gauge across the board, so I figure the power numbers won’t be bad once its totally dialed in (got a adj fuel pressure reg to thrown also want to put in a rebuild AFM, new 02 sensor and do the exhaust once the spec system is finalized).

overall it wasn’t bad just keep everything clean and have a good toque wrench and if possible get new hardware for all the engine bolts (I think they are all torque to yield, you probably can reuse them, I know a lot of people who do with no problems, but I wouldn’t recommend it on something your going to beat on pretty hard)

#7

Greg Lockman wrote:

[quote]I rebuilt the engine in my car last winter. We went low buck; left the engine in the car pulled the head and dropped the pan and just put fresh bearings (rod and mains) and re-ringed it (crank and cyl walls looked good so we left them alone and used factory sized stuff). also replaced all the wear items (oil pump, water pump, timing belt, etc…). Overall it runs strong I don’t have any dyno numbers (still in DE land) but I have about 150-160-ish psi on the leak down gauge across the board, so I figure the power numbers won’t be bad once its totally dialed in (got a adj fuel pressure reg to thrown also want to put in a rebuild AFM, new 02 sensor and do the exhaust once the spec system is finalized).

overall it wasn’t bad just keep everything clean and have a good toque wrench and if possible get new hardware for all the engine bolts (I think they are all torque to yield, you probably can reuse them, I know a lot of people who do with no problems, but I wouldn’t recommend it on something your going to beat on pretty hard)[/quote]

how much do you think this style of budget rebuild cost you?? I may need to do the same on mine. What did you do to the head?? send it out?? Or just replace the valve guides and seals?? let me know.

#8

I don’t recall the exact numbers, but they were similar to ed’s. Like $500-600 for the parts (bearings, new bolts, gaskets, oil pump, belts, etc…) and like another $250ish (I think it was a little more, got to dig up the receipt, NJ machine shops are pricier). They basically just overhauled the head, new springs , guides and recut the seats and reground the valves. Basically like $800-900 and a weekend I had it rebuilt and ready to go.